Building code base for loading more & refresh lists with jetpack paging lib

Thursday, 11/06/2020

Tram Ho

Preamble

Loading data lists with more load and refreshing is a very common task in the android dev process, today I introduce you how to do it with jetpack paging lib and create bases to reuse for different screens. .

Proceed to the code base

PagedListAdapter

To paging lib can detect the load more then we need to use PagedListAdapter , you can create an adapter or extend from BasePagedListAdapter below.

Note: paging lib uses getItem() function to detect the load more so you need to call this function in onBindViewHolder() , if you use another way to get item, for example adapter.currentList.getPosition , paging lib will Could not detect loading more list.

<span class="token keyword">abstract</span> <span class="token keyword">class</span> BasePagedListAdapter <span class="token operator">&lt;</span> Item <span class="token punctuation">,</span> ViewBinding <span class="token operator">:</span> ViewDataBinding <span class="token operator">&gt;</span> <span class="token punctuation">(</span>
    callBack <span class="token operator">:</span> DiffUtil <span class="token punctuation">.</span> ItemCallback <span class="token operator">&lt;</span> Item <span class="token operator">&gt;</span>
<span class="token punctuation">)</span> <span class="token operator">:</span> PagedListAdapter <span class="token operator">&lt;</span> Item <span class="token punctuation">,</span> BaseViewHolder <span class="token operator">&lt;</span> ViewBinding <span class="token operator">&gt;</span> <span class="token operator">&gt;</span> <span class="token punctuation">(</span> callBack <span class="token punctuation">)</span> <span class="token punctuation">{</span>

    <span class="token keyword">override</span> <span class="token keyword">fun</span> <span class="token function">onCreateViewHolder</span> <span class="token punctuation">(</span> parent <span class="token operator">:</span> ViewGroup <span class="token punctuation">,</span> viewType <span class="token operator">:</span> Int <span class="token punctuation">)</span> <span class="token operator">:</span> BaseViewHolder <span class="token operator">&lt;</span> ViewBinding <span class="token operator">&gt;</span> <span class="token punctuation">{</span>
        <span class="token keyword">return</span> <span class="token function">BaseViewHolder</span> <span class="token punctuation">(</span> DataBindingUtil <span class="token punctuation">.</span> inflate <span class="token operator">&lt;</span> ViewBinding <span class="token operator">&gt;</span> <span class="token punctuation">(</span>
            LayoutInflater <span class="token punctuation">.</span> <span class="token function">from</span> <span class="token punctuation">(</span> parent <span class="token punctuation">.</span> context <span class="token punctuation">)</span> <span class="token punctuation">,</span>
            <span class="token function">getLayoutRes</span> <span class="token punctuation">(</span> viewType <span class="token punctuation">)</span> <span class="token punctuation">,</span>
            parent <span class="token punctuation">,</span> <span class="token boolean">false</span>
        <span class="token punctuation">)</span> <span class="token punctuation">.</span> <span class="token function">apply</span> <span class="token punctuation">{</span>
            <span class="token function">bindFirstTime</span> <span class="token punctuation">(</span> <span class="token keyword">this</span> <span class="token punctuation">)</span>
        <span class="token punctuation">}</span> <span class="token punctuation">)</span>
    <span class="token punctuation">}</span>

    <span class="token keyword">override</span> <span class="token keyword">fun</span> <span class="token function">onBindViewHolder</span> <span class="token punctuation">(</span> holder <span class="token operator">:</span> BaseViewHolder <span class="token operator">&lt;</span> ViewBinding <span class="token operator">&gt;</span> <span class="token punctuation">,</span> position <span class="token operator">:</span> Int <span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">val</span> item <span class="token operator">:</span> Item <span class="token operator">?</span> <span class="token operator">=</span> <span class="token function">getItem</span> <span class="token punctuation">(</span> position <span class="token punctuation">)</span>
        holder <span class="token punctuation">.</span> binding <span class="token punctuation">.</span> <span class="token function">setVariable</span> <span class="token punctuation">(</span> BR <span class="token punctuation">.</span> item <span class="token punctuation">,</span> item <span class="token punctuation">)</span>
        <span class="token keyword">if</span> <span class="token punctuation">(</span> item <span class="token operator">!=</span> <span class="token keyword">null</span> <span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token function">bindView</span> <span class="token punctuation">(</span> holder <span class="token punctuation">.</span> binding <span class="token punctuation">,</span> item <span class="token punctuation">,</span> position <span class="token punctuation">)</span>
        <span class="token punctuation">}</span>
        holder <span class="token punctuation">.</span> binding <span class="token punctuation">.</span> <span class="token function">executePendingBindings</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span>
    <span class="token punctuation">}</span>

    <span class="token comment">/**
     * get layout res based on view type
     */</span>
    <span class="token keyword">protected</span> <span class="token keyword">abstract</span> <span class="token keyword">fun</span> <span class="token function">getLayoutRes</span> <span class="token punctuation">(</span> viewType <span class="token operator">:</span> Int <span class="token punctuation">)</span> <span class="token operator">:</span> Int

    <span class="token comment">/**
     * bind first time
     * use for set item onClickListener, something only set one time
     */</span>
    <span class="token keyword">protected</span> <span class="token keyword">open</span> <span class="token keyword">fun</span> <span class="token function">bindFirstTime</span> <span class="token punctuation">(</span> binding <span class="token operator">:</span> ViewBinding <span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token punctuation">}</span>

    <span class="token comment">/**
     * bind view
     */</span>
    <span class="token keyword">protected</span> <span class="token keyword">open</span> <span class="token keyword">fun</span> <span class="token function">bindView</span> <span class="token punctuation">(</span> binding <span class="token operator">:</span> ViewBinding <span class="token punctuation">,</span> item <span class="token operator">:</span> Item <span class="token punctuation">,</span> position <span class="token operator">:</span> Int <span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token punctuation">}</span>
<span class="token punctuation">}</span>

abstract class BasePagedListAdapter < Item , ViewBinding : ViewDataBinding > (

callBack : DiffUtil . ItemCallback < Item >

) : PagedListAdapter < Item , BaseViewHolder < ViewBinding > > ( callBack ) {

override fun onCreateViewHolder ( parent : ViewGroup , viewType : Int ) : BaseViewHolder < ViewBinding > {

return BaseViewHolder ( DataBindingUtil . inflate < ViewBinding > (

LayoutInflater . from ( parent . context ) ,

getLayoutRes ( viewType ) ,

parent , false

) . apply {

bindFirstTime ( this )

} )

}

override fun onBindViewHolder ( holder : BaseViewHolder < ViewBinding > , position : Int ) {

val item : Item ? = getItem ( position )

holder . binding . setVariable ( BR . item , item )

if ( item != null ) {

bindView ( holder . binding , item , position )

}

holder . binding . executePendingBindings ( )

}

/**

* get layout res based on view type

*/

protected abstract fun getLayoutRes ( viewType : Int ) : Int

/**

* bind first time

* use for set item onClickListener, something only set one time

*/

protected open fun bindFirstTime ( binding : ViewBinding ) { }

/**

* bind view

*/

protected open fun bindView ( binding : ViewBinding , item : Item , position : Int ) { }

}

https://github.com/dangquanuet/The-Movie-DB-Kotlin/blob/develop/app/src/main/java/com/example/moviedb/ui/base/BaseListAdapter.kt#L80

BasePageKeyedDataSource

Paging lib currently supports 3 different types of data srouce, but PageKeyedDataSource is the most commonly used type so I will make an example of this type, the other 2 types you can do the same.

Currently PageKeyedDataSource has 3 functions loadInitial() , loadBefore() , loadAfter() to define the load status according to the page, but in fact I see that we only need a load function, so I have shortened the code. and returns a unique abstract loadDataSource() function.

Note: As far as I know, paging 3 (currently in preview) has combined the above functions into 1, really very reasonable. I will introduce it to you after it is more stable.

<span class="token comment">/**
 * page keyed data source uses page number to request data
 */</span>
<span class="token keyword">abstract</span> <span class="token keyword">class</span> BasePageKeyedDataSource <span class="token operator">&lt;</span> Item <span class="token operator">&gt;</span> <span class="token punctuation">(</span>
    <span class="token keyword">private</span> <span class="token keyword">val</span> viewModel <span class="token operator">:</span> BasePagedRefreshViewModel <span class="token operator">&lt;</span> Item <span class="token operator">&gt;</span>
<span class="token punctuation">)</span> <span class="token operator">:</span> PageKeyedDataSource <span class="token operator">&lt;</span> Int <span class="token punctuation">,</span> Item <span class="token operator">&gt;</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span> <span class="token punctuation">{</span>

    <span class="token comment">/**
     * load first page
     */</span>
    <span class="token keyword">override</span> <span class="token keyword">fun</span> <span class="token function">loadInitial</span> <span class="token punctuation">(</span>
        params <span class="token operator">:</span> LoadInitialParams <span class="token operator">&lt;</span> Int <span class="token operator">&gt;</span> <span class="token punctuation">,</span>
        callback <span class="token operator">:</span> LoadInitialCallback <span class="token operator">&lt;</span> Int <span class="token punctuation">,</span> Item <span class="token operator">&gt;</span>
    <span class="token punctuation">)</span> <span class="token punctuation">{</span>
        viewModel <span class="token punctuation">.</span> viewModelScope <span class="token punctuation">.</span> <span class="token function">launch</span> <span class="token punctuation">{</span>
            <span class="token keyword">try</span> <span class="token punctuation">{</span>
                viewModel <span class="token punctuation">.</span> <span class="token function">showLoading</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span>
                <span class="token keyword">val</span> itemList <span class="token operator">=</span> <span class="token function">loadDataSource</span> <span class="token punctuation">(</span> loadInitialParams <span class="token operator">=</span> params <span class="token punctuation">)</span>
                viewModel <span class="token punctuation">.</span> isEmptyList <span class="token punctuation">.</span> value <span class="token operator">=</span> itemList <span class="token punctuation">.</span> <span class="token function">isEmpty</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span>
                callback <span class="token punctuation">.</span> <span class="token function">onResult</span> <span class="token punctuation">(</span>
                    itemList <span class="token punctuation">,</span>
                    <span class="token keyword">null</span> <span class="token punctuation">,</span>
                    <span class="token comment">// last page</span>
                    <span class="token keyword">if</span> <span class="token punctuation">(</span> itemList <span class="token punctuation">.</span> size <span class="token operator">&lt;</span> viewModel <span class="token punctuation">.</span> pageSize <span class="token punctuation">)</span> <span class="token keyword">null</span>
                    <span class="token comment">// load next page</span>
                    <span class="token keyword">else</span> viewModel <span class="token punctuation">.</span> firstPage <span class="token operator">+</span> <span class="token number">1</span>
                <span class="token punctuation">)</span>
            <span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span> e <span class="token operator">:</span> Throwable <span class="token punctuation">)</span> <span class="token punctuation">{</span>
                viewModel <span class="token punctuation">.</span> <span class="token function">onError</span> <span class="token punctuation">(</span> e <span class="token punctuation">)</span>
            <span class="token punctuation">}</span> <span class="token keyword">finally</span> <span class="token punctuation">{</span>
                viewModel <span class="token punctuation">.</span> <span class="token function">hideLoadMoreRefresh</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span>
            <span class="token punctuation">}</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>

    <span class="token comment">/**
     * load previous page
     */</span>
    <span class="token keyword">override</span> <span class="token keyword">fun</span> <span class="token function">loadBefore</span> <span class="token punctuation">(</span> params <span class="token operator">:</span> LoadParams <span class="token operator">&lt;</span> Int <span class="token operator">&gt;</span> <span class="token punctuation">,</span> callback <span class="token operator">:</span> LoadCallback <span class="token operator">&lt;</span> Int <span class="token punctuation">,</span> Item <span class="token operator">&gt;</span> <span class="token punctuation">)</span> <span class="token punctuation">{</span>
        viewModel <span class="token punctuation">.</span> viewModelScope <span class="token punctuation">.</span> <span class="token function">launch</span> <span class="token punctuation">{</span>
            <span class="token keyword">try</span> <span class="token punctuation">{</span>
                <span class="token keyword">val</span> itemList <span class="token operator">=</span> <span class="token function">loadDataSource</span> <span class="token punctuation">(</span> loadParams <span class="token operator">=</span> params <span class="token punctuation">)</span>
                callback <span class="token punctuation">.</span> <span class="token function">onResult</span> <span class="token punctuation">(</span>
                    itemList <span class="token punctuation">,</span>
                    <span class="token comment">// is first page</span>
                    <span class="token keyword">if</span> <span class="token punctuation">(</span> params <span class="token punctuation">.</span> key <span class="token operator">==</span> viewModel <span class="token punctuation">.</span> firstPage <span class="token punctuation">)</span> <span class="token keyword">null</span>
                    <span class="token keyword">else</span> <span class="token punctuation">(</span> params <span class="token punctuation">.</span> key <span class="token operator">-</span> <span class="token number">1</span> <span class="token punctuation">)</span>
                <span class="token punctuation">)</span>
            <span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span> e <span class="token operator">:</span> Throwable <span class="token punctuation">)</span> <span class="token punctuation">{</span>
                viewModel <span class="token punctuation">.</span> <span class="token function">onError</span> <span class="token punctuation">(</span> e <span class="token punctuation">)</span>
            <span class="token punctuation">}</span> <span class="token keyword">finally</span> <span class="token punctuation">{</span>
                viewModel <span class="token punctuation">.</span> <span class="token function">hideLoadMoreRefresh</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span>
            <span class="token punctuation">}</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>

    <span class="token comment">/**
     * load next page
     */</span>
    <span class="token keyword">override</span> <span class="token keyword">fun</span> <span class="token function">loadAfter</span> <span class="token punctuation">(</span> params <span class="token operator">:</span> LoadParams <span class="token operator">&lt;</span> Int <span class="token operator">&gt;</span> <span class="token punctuation">,</span> callback <span class="token operator">:</span> LoadCallback <span class="token operator">&lt;</span> Int <span class="token punctuation">,</span> Item <span class="token operator">&gt;</span> <span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token comment">// disable load more when loading or refresh</span>
        <span class="token keyword">if</span> <span class="token punctuation">(</span> viewModel <span class="token punctuation">.</span> isLoading <span class="token punctuation">.</span> value <span class="token operator">==</span> <span class="token boolean">true</span> <span class="token operator">||</span> viewModel <span class="token punctuation">.</span> isRefresh <span class="token punctuation">.</span> value <span class="token operator">==</span> <span class="token boolean">true</span> <span class="token punctuation">)</span> <span class="token keyword">return</span>

        viewModel <span class="token punctuation">.</span> viewModelScope <span class="token punctuation">.</span> <span class="token function">launch</span> <span class="token punctuation">{</span>
            <span class="token keyword">try</span> <span class="token punctuation">{</span>
                viewModel <span class="token punctuation">.</span> isLoadMore <span class="token punctuation">.</span> value <span class="token operator">=</span> <span class="token boolean">true</span>
                <span class="token keyword">val</span> itemList <span class="token operator">=</span> <span class="token function">loadDataSource</span> <span class="token punctuation">(</span> loadParams <span class="token operator">=</span> params <span class="token punctuation">)</span>
                callback <span class="token punctuation">.</span> <span class="token function">onResult</span> <span class="token punctuation">(</span>
                    itemList <span class="token punctuation">,</span>
                    <span class="token comment">// last page</span>
                    <span class="token keyword">if</span> <span class="token punctuation">(</span> itemList <span class="token punctuation">.</span> size <span class="token operator">&lt;</span> viewModel <span class="token punctuation">.</span> pageSize <span class="token punctuation">)</span> <span class="token keyword">null</span>
                    <span class="token comment">// load next page</span>
                    <span class="token keyword">else</span> <span class="token punctuation">(</span> params <span class="token punctuation">.</span> key <span class="token operator">+</span> <span class="token number">1</span> <span class="token punctuation">)</span>
                <span class="token punctuation">)</span>
            <span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span> e <span class="token operator">:</span> Throwable <span class="token punctuation">)</span> <span class="token punctuation">{</span>
                viewModel <span class="token punctuation">.</span> <span class="token function">onError</span> <span class="token punctuation">(</span> e <span class="token punctuation">)</span>
            <span class="token punctuation">}</span> <span class="token keyword">finally</span> <span class="token punctuation">{</span>
                viewModel <span class="token punctuation">.</span> <span class="token function">hideLoadMoreRefresh</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span>
            <span class="token punctuation">}</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>

    <span class="token comment">/**
     * load data
     */</span>
    <span class="token keyword">abstract</span> <span class="token keyword">suspend</span> <span class="token keyword">fun</span> <span class="token function">loadDataSource</span> <span class="token punctuation">(</span>
        loadInitialParams <span class="token operator">:</span> LoadInitialParams <span class="token operator">&lt;</span> Int <span class="token operator">&gt;</span> <span class="token operator">?</span> <span class="token operator">=</span> <span class="token keyword">null</span> <span class="token punctuation">,</span>
        loadParams <span class="token operator">:</span> LoadParams <span class="token operator">&lt;</span> Int <span class="token operator">&gt;</span> <span class="token operator">?</span> <span class="token operator">=</span> <span class="token keyword">null</span>
    <span class="token punctuation">)</span> <span class="token operator">:</span> List <span class="token operator">&lt;</span> Item <span class="token operator">&gt;</span>
<span class="token punctuation">}</span>

/**

* page keyed data source uses page number to request data

*/

abstract class BasePageKeyedDataSource < Item > (

private val viewModel : BasePagedRefreshViewModel < Item >

) : PageKeyedDataSource < Int , Item > ( ) {

/**

* load first page

*/

override fun loadInitial (

params : LoadInitialParams < Int > ,

callback : LoadInitialCallback < Int , Item >

) {

viewModel . viewModelScope . launch {

try {

viewModel . showLoading ( )

val itemList = loadDataSource ( loadInitialParams = params )

viewModel . isEmptyList . value = itemList . isEmpty ( )

callback . onResult (

itemList ,

null ,

// last page

if ( itemList . size < viewModel . pageSize ) null

// load next page

else viewModel . firstPage + 1

)

} catch ( e : Throwable ) {

viewModel . onError ( e )

} finally {

viewModel . hideLoadMoreRefresh ( )

}

/**

* load previous page

*/

override fun loadBefore ( params : LoadParams < Int > , callback : LoadCallback < Int , Item > ) {

viewModel . viewModelScope . launch {

try {

val itemList = loadDataSource ( loadParams = params )

callback . onResult (

itemList ,

// is first page

if ( params . key == viewModel . firstPage ) null

else ( params . key - 1 )

)

viewModel . onError ( e )

} finally {

viewModel . hideLoadMoreRefresh ( )

}

/**

* load next page

*/

override fun loadAfter ( params : LoadParams < Int > , callback : LoadCallback < Int , Item > ) {

// disable load more when loading or refresh

if ( viewModel . isLoading . value == true || viewModel . isRefresh . value == true ) return

viewModel . viewModelScope . launch {

try {

viewModel . isLoadMore . value = true

val itemList = loadDataSource ( loadParams = params )

callback . onResult (

itemList ,

// last page

// load next page

else ( params . key + 1 )

)

viewModel . onError ( e )

} finally {

viewModel . hideLoadMoreRefresh ( )

}

/**

* load data

*/

abstract suspend fun loadDataSource (

loadInitialParams : LoadInitialParams < Int > ? = null ,

loadParams : LoadParams < Int > ? = null

) : List < Item >

}

https://github.com/dangquanuet/The-Movie-DB-Kotlin/blob/develop/app/src/main/java/com/example/moviedb/ui/base/BasePagedRefreshViewModel.kt#L123

BasePagedRefreshViewModel

After having the data source, we will define the viewmodel, the viewmodel will have the basic logic of loading more, refreshing, PageKeyedDataSource parameters for PageKeyedDataSource and a loadData() function to get data.

<span class="token keyword">abstract</span> <span class="token keyword">class</span> BasePagedRefreshViewModel <span class="token operator">&lt;</span> Item <span class="token operator">&gt;</span> <span class="token operator">:</span> <span class="token function">BaseViewModel</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span> <span class="token punctuation">{</span>

    <span class="token comment">// first page number of item list</span>
    <span class="token keyword">open</span> <span class="token keyword">val</span> firstPage <span class="token operator">=</span> Constants <span class="token punctuation">.</span> DEFAULT_FIRST_PAGE

    <span class="token comment">// number visible threshold</span>
    <span class="token keyword">open</span> <span class="token keyword">val</span> prefetchDistance <span class="token operator">=</span> Constants <span class="token punctuation">.</span> DEFAULT_NUM_VISIBLE_THRESHOLD

    <span class="token comment">// number item per page</span>
    <span class="token keyword">open</span> <span class="token keyword">val</span> pageSize <span class="token operator">=</span> Constants <span class="token punctuation">.</span> DEFAULT_ITEM_PER_PAGE

    <span class="token comment">// refresh flag</span>
    <span class="token keyword">val</span> isRefresh <span class="token operator">=</span> <span class="token function">MutableLiveData</span> <span class="token punctuation">(</span> <span class="token boolean">false</span> <span class="token punctuation">)</span>

    <span class="token comment">// load more flag</span>
    <span class="token keyword">val</span> isLoadMore <span class="token operator">=</span> <span class="token function">MutableLiveData</span> <span class="token punctuation">(</span> <span class="token boolean">false</span> <span class="token punctuation">)</span>

    <span class="token comment">// enable refresh when not loading or not load more</span>
    <span class="token keyword">val</span> enableRefresh <span class="token operator">=</span> MediatorLiveData <span class="token operator">&lt;</span> Boolean <span class="token operator">&gt;</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span> <span class="token punctuation">.</span> <span class="token function">apply</span> <span class="token punctuation">{</span>
        value <span class="token operator">=</span> <span class="token boolean">true</span>
        <span class="token function">addSource</span> <span class="token punctuation">(</span> isLoading <span class="token punctuation">)</span> <span class="token punctuation">{</span>
            value <span class="token operator">=</span> <span class="token operator">!</span> <span class="token punctuation">(</span> isLoading <span class="token punctuation">.</span> value <span class="token operator">==</span> <span class="token boolean">true</span> <span class="token operator">||</span> isLoadMore <span class="token punctuation">.</span> value <span class="token operator">==</span> <span class="token boolean">true</span> <span class="token punctuation">)</span>
        <span class="token punctuation">}</span>
        <span class="token function">addSource</span> <span class="token punctuation">(</span> isLoadMore <span class="token punctuation">)</span> <span class="token punctuation">{</span>
            value <span class="token operator">=</span> <span class="token operator">!</span> <span class="token punctuation">(</span> isLoading <span class="token punctuation">.</span> value <span class="token operator">==</span> <span class="token boolean">true</span> <span class="token operator">||</span> isLoadMore <span class="token punctuation">.</span> value <span class="token operator">==</span> <span class="token boolean">true</span> <span class="token punctuation">)</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>

    <span class="token comment">// data source</span>
    <span class="token keyword">private</span> <span class="token keyword">var</span> dataSource <span class="token operator">:</span> BasePageKeyedDataSource <span class="token operator">&lt;</span> Item <span class="token operator">&gt;</span> <span class="token operator">?</span> <span class="token operator">=</span> <span class="token keyword">null</span>

    <span class="token comment">// paged list config</span>
    <span class="token keyword">private</span> <span class="token keyword">val</span> pagedListConfig <span class="token operator">:</span> PagedList <span class="token punctuation">.</span> Config <span class="token keyword">by</span> lazy <span class="token punctuation">{</span>
        PagedList <span class="token punctuation">.</span> Config <span class="token punctuation">.</span> <span class="token function">Builder</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span>
            <span class="token punctuation">.</span> <span class="token function">setEnablePlaceholders</span> <span class="token punctuation">(</span> <span class="token boolean">false</span> <span class="token punctuation">)</span>
            <span class="token punctuation">.</span> <span class="token function">setInitialLoadSizeHint</span> <span class="token punctuation">(</span> <span class="token number">2</span> <span class="token operator">*</span> pageSize <span class="token punctuation">)</span>
            <span class="token punctuation">.</span> <span class="token function">setPageSize</span> <span class="token punctuation">(</span> pageSize <span class="token punctuation">)</span>
            <span class="token punctuation">.</span> <span class="token function">setPrefetchDistance</span> <span class="token punctuation">(</span> prefetchDistance <span class="token punctuation">)</span>
            <span class="token punctuation">.</span> <span class="token function">build</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span>
    <span class="token punctuation">}</span>

    <span class="token comment">// item list</span>
    <span class="token keyword">val</span> itemList <span class="token operator">:</span> LiveData <span class="token operator">&lt;</span> PagedList <span class="token operator">&lt;</span> Item <span class="token operator">&gt;</span> <span class="token operator">&gt;</span> <span class="token keyword">by</span> lazy <span class="token punctuation">{</span>
        <span class="token function">LivePagedListBuilder</span> <span class="token punctuation">(</span>
            <span class="token keyword">object</span> <span class="token operator">:</span> DataSource <span class="token punctuation">.</span> Factory <span class="token operator">&lt;</span> Int <span class="token punctuation">,</span> Item <span class="token operator">&gt;</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span> <span class="token punctuation">{</span>
                <span class="token keyword">override</span> <span class="token keyword">fun</span> <span class="token function">create</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span> <span class="token operator">:</span> DataSource <span class="token operator">&lt;</span> Int <span class="token punctuation">,</span> Item <span class="token operator">&gt;</span> <span class="token punctuation">{</span>
                    <span class="token keyword">return</span> <span class="token function">createDataSource</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span>
                <span class="token punctuation">}</span>
            <span class="token punctuation">}</span> <span class="token punctuation">,</span> pagedListConfig
        <span class="token punctuation">)</span> <span class="token punctuation">.</span> <span class="token function">build</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span>
    <span class="token punctuation">}</span>

    <span class="token comment">// empty list flag</span>
    <span class="token keyword">val</span> isEmptyList <span class="token operator">=</span> <span class="token function">MutableLiveData</span> <span class="token punctuation">(</span> <span class="token boolean">false</span> <span class="token punctuation">)</span>

    <span class="token comment">/**
     * refresh data
     */</span>
    <span class="token keyword">fun</span> <span class="token function">doRefresh</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span> <span class="token punctuation">{</span>
        isRefresh <span class="token punctuation">.</span> value <span class="token operator">=</span> <span class="token boolean">true</span>
        dataSource <span class="token operator">?</span> <span class="token punctuation">.</span> <span class="token function">invalidate</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span>
    <span class="token punctuation">}</span>

    <span class="token comment">/**
     * create page keyed data source
     */</span>
    <span class="token keyword">open</span> <span class="token keyword">fun</span> <span class="token function">createDataSource</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span> <span class="token operator">:</span> BasePageKeyedDataSource <span class="token operator">&lt;</span> Item <span class="token operator">&gt;</span> <span class="token punctuation">{</span>
        <span class="token keyword">return</span> <span class="token keyword">object</span> <span class="token operator">:</span> BasePageKeyedDataSource <span class="token operator">&lt;</span> Item <span class="token operator">&gt;</span> <span class="token punctuation">(</span> viewModel <span class="token operator">=</span> <span class="token keyword">this</span> <span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token keyword">override</span> <span class="token keyword">suspend</span> <span class="token keyword">fun</span> <span class="token function">loadDataSource</span> <span class="token punctuation">(</span>
                loadInitialParams <span class="token operator">:</span> LoadInitialParams <span class="token operator">&lt;</span> Int <span class="token operator">&gt;</span> <span class="token operator">?</span> <span class="token punctuation">,</span>
                loadParams <span class="token operator">:</span> LoadParams <span class="token operator">&lt;</span> Int <span class="token operator">&gt;</span> <span class="token operator">?</span>
            <span class="token punctuation">)</span> <span class="token operator">:</span> List <span class="token operator">&lt;</span> Item <span class="token operator">&gt;</span> <span class="token punctuation">{</span>
                <span class="token keyword">return</span> <span class="token function">loadData</span> <span class="token punctuation">(</span> loadInitialParams <span class="token punctuation">,</span> loadParams <span class="token punctuation">)</span>
            <span class="token punctuation">}</span>
        <span class="token punctuation">}</span> <span class="token punctuation">.</span> <span class="token function">apply</span> <span class="token punctuation">{</span>
            dataSource <span class="token operator">=</span> <span class="token keyword">this</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>

    <span class="token comment">/**
     * load and return item list from server
     */</span>
    <span class="token keyword">abstract</span> <span class="token keyword">suspend</span> <span class="token keyword">fun</span> <span class="token function">loadData</span> <span class="token punctuation">(</span>
        loadInitialParams <span class="token operator">:</span> PageKeyedDataSource <span class="token punctuation">.</span> LoadInitialParams <span class="token operator">&lt;</span> Int <span class="token operator">&gt;</span> <span class="token operator">?</span> <span class="token punctuation">,</span>
        loadParams <span class="token operator">:</span> PageKeyedDataSource <span class="token punctuation">.</span> LoadParams <span class="token operator">&lt;</span> Int <span class="token operator">&gt;</span> <span class="token operator">?</span>
    <span class="token punctuation">)</span> <span class="token operator">:</span> List <span class="token operator">&lt;</span> Item <span class="token operator">&gt;</span>

    <span class="token comment">/**
     * handler error
     */</span>
    <span class="token keyword">override</span> <span class="token keyword">suspend</span> <span class="token keyword">fun</span> <span class="token function">onError</span> <span class="token punctuation">(</span> throwable <span class="token operator">:</span> Throwable <span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">super</span> <span class="token punctuation">.</span> <span class="token function">onError</span> <span class="token punctuation">(</span> throwable <span class="token punctuation">)</span>
        <span class="token comment">// reset load</span>
        <span class="token function">hideLoadMoreRefresh</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span>
    <span class="token punctuation">}</span>

    <span class="token comment">/**
     * hide loading, load more and refresh indicator
     */</span>
    <span class="token keyword">fun</span> <span class="token function">hideLoadMoreRefresh</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token function">hideLoading</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span>
        isRefresh <span class="token punctuation">.</span> value <span class="token operator">=</span> <span class="token boolean">false</span>
        isLoadMore <span class="token punctuation">.</span> value <span class="token operator">=</span> <span class="token boolean">false</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>

100

101

102

103

104

105

106

abstract class BasePagedRefreshViewModel < Item > : BaseViewModel ( ) {

// first page number of item list

open val firstPage = Constants . DEFAULT_FIRST_PAGE

// number visible threshold

open val prefetchDistance = Constants . DEFAULT_NUM_VISIBLE_THRESHOLD

// number item per page

open val pageSize = Constants . DEFAULT_ITEM_PER_PAGE

// refresh flag

val isRefresh = MutableLiveData ( false )

// load more flag

val isLoadMore = MutableLiveData ( false )

// enable refresh when not loading or not load more

val enableRefresh = MediatorLiveData < Boolean > ( ) . apply {

value = true

addSource ( isLoading ) {

value = ! ( isLoading . value == true || isLoadMore . value == true )

}

addSource ( isLoadMore ) {

}

// data source

private var dataSource : BasePageKeyedDataSource < Item > ? = null

// paged list config

private val pagedListConfig : PagedList . Config by lazy {

PagedList . Config . Builder ( )

. setEnablePlaceholders ( false )

. setInitialLoadSizeHint ( 2 * pageSize )

. setPageSize ( pageSize )

. setPrefetchDistance ( prefetchDistance )

. build ( )

}

// item list

val itemList : LiveData < PagedList < Item > > by lazy {

LivePagedListBuilder (

object : DataSource . Factory < Int , Item > ( ) {

override fun create ( ) : DataSource < Int , Item > {

return createDataSource ( )

}

} , pagedListConfig

) . build ( )

}

// empty list flag

val isEmptyList = MutableLiveData ( false )

/**

* refresh data

*/

fun doRefresh ( ) {

isRefresh . value = true

dataSource ? . invalidate ( )

}

/**

* create page keyed data source

*/

open fun createDataSource ( ) : BasePageKeyedDataSource < Item > {

return object : BasePageKeyedDataSource < Item > ( viewModel = this ) {

override suspend fun loadDataSource (

loadParams : LoadParams < Int > ?

) : List < Item > {

return loadData ( loadInitialParams , loadParams )

}

} . apply {

dataSource = this

}

/**

* load and return item list from server

*/

loadInitialParams : PageKeyedDataSource . LoadInitialParams < Int > ? ,

loadParams : PageKeyedDataSource . LoadParams < Int > ?

) : List < Item >

/**

* handler error

*/

override suspend fun onError ( throwable : Throwable ) {

super . onError ( throwable )

// reset load

hideLoadMoreRefresh ( )

}

/**

* hide loading, load more and refresh indicator

*/

fun hideLoadMoreRefresh ( ) {

hideLoading ( )

isRefresh . value = false

isLoadMore . value = false

}

https://github.com/dangquanuet/The-Movie-DB-Kotlin/blob/develop/app/src/main/java/com/example/moviedb/ui/base/BasePagedRefreshViewModel.kt#L14

BasePagedRefreshFragment

The base code fragment for the monitor uses the BasePagedRefreshViewModel so we can reuse it for different screens that have the same mechanism.

<span class="token keyword">abstract</span> <span class="token keyword">class</span> BasePagedRefreshFragment <span class="token operator">&lt;</span> ViewBinding <span class="token operator">:</span> ViewDataBinding <span class="token punctuation">,</span> ViewModel <span class="token operator">:</span> BasePagedRefreshViewModel <span class="token operator">&lt;</span> Item <span class="token operator">&gt;</span> <span class="token punctuation">,</span> Item <span class="token operator">&gt;</span> <span class="token operator">:</span>
    BaseFragment <span class="token operator">&lt;</span> ViewBinding <span class="token punctuation">,</span> ViewModel <span class="token operator">&gt;</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span> <span class="token punctuation">{</span>

    <span class="token keyword">override</span> <span class="token keyword">val</span> layoutId <span class="token operator">:</span> Int <span class="token operator">=</span> R <span class="token punctuation">.</span> layout <span class="token punctuation">.</span> fragment_paged_refresh

    <span class="token keyword">abstract</span> <span class="token keyword">val</span> pagedListAdapter <span class="token operator">:</span> BasePagedListAdapter <span class="token operator">&lt;</span> Item <span class="token punctuation">,</span> <span class="token keyword">out</span> ViewDataBinding <span class="token operator">&gt;</span>

    <span class="token keyword">open</span> <span class="token keyword">fun</span> <span class="token function">getLayoutManager</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span> <span class="token operator">:</span> RecyclerView <span class="token punctuation">.</span> LayoutManager <span class="token operator">=</span>
        <span class="token function">LinearLayoutManager</span> <span class="token punctuation">(</span> context <span class="token punctuation">,</span> LinearLayoutManager <span class="token punctuation">.</span> VERTICAL <span class="token punctuation">,</span> <span class="token boolean">false</span> <span class="token punctuation">)</span>

    <span class="token keyword">override</span> <span class="token keyword">fun</span> <span class="token function">onActivityCreated</span> <span class="token punctuation">(</span> savedInstanceState <span class="token operator">:</span> Bundle <span class="token operator">?</span> <span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">super</span> <span class="token punctuation">.</span> <span class="token function">onActivityCreated</span> <span class="token punctuation">(</span> savedInstanceState <span class="token punctuation">)</span>
        <span class="token function">setupPagedRefresh</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span>
    <span class="token punctuation">}</span>

    <span class="token comment">/**
     * setup default paged refresh
     */</span>
    <span class="token keyword">open</span> <span class="token keyword">fun</span> <span class="token function">setupPagedRefresh</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span> <span class="token punctuation">{</span>
        refresh_layout <span class="token operator">?</span> <span class="token punctuation">.</span> <span class="token function">setOnRefreshListener</span> <span class="token punctuation">{</span>
            viewModel <span class="token punctuation">.</span> <span class="token function">doRefresh</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span>
        <span class="token punctuation">}</span>
        recycler_view <span class="token operator">?</span> <span class="token punctuation">.</span> layoutManager <span class="token operator">=</span> <span class="token function">getLayoutManager</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span>
        recycler_view <span class="token operator">?</span> <span class="token punctuation">.</span> adapter <span class="token operator">=</span> pagedListAdapter
        viewModel <span class="token punctuation">.</span> <span class="token function">apply</span> <span class="token punctuation">{</span>
            itemList <span class="token punctuation">.</span> <span class="token function">observe</span> <span class="token punctuation">(</span> viewLifecycleOwner <span class="token punctuation">,</span> Observer <span class="token punctuation">{</span>
                pagedListAdapter <span class="token punctuation">.</span> <span class="token function">submitList</span> <span class="token punctuation">(</span> it <span class="token punctuation">)</span>
            <span class="token punctuation">}</span> <span class="token punctuation">)</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>

    <span class="token keyword">override</span> <span class="token keyword">fun</span> <span class="token function">handleLoading</span> <span class="token punctuation">(</span> isLoading <span class="token operator">:</span> Boolean <span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token comment">// use progress bar</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>

abstract class BasePagedRefreshFragment < ViewBinding : ViewDataBinding , ViewModel : BasePagedRefreshViewModel < Item > , Item > :

BaseFragment < ViewBinding , ViewModel > ( ) {

override val layoutId : Int = R . layout . fragment_paged_refresh

abstract val pagedListAdapter : BasePagedListAdapter < Item , out ViewDataBinding >

open fun getLayoutManager ( ) : RecyclerView . LayoutManager =

LinearLayoutManager ( context , LinearLayoutManager . VERTICAL , false )

override fun onActivityCreated ( savedInstanceState : Bundle ? ) {

super . onActivityCreated ( savedInstanceState )

setupPagedRefresh ( )

}

/**

* setup default paged refresh

*/

open fun setupPagedRefresh ( ) {

refresh_layout ? . setOnRefreshListener {

viewModel . doRefresh ( )

}

recycler_view ? . layoutManager = getLayoutManager ( )

recycler_view ? . adapter = pagedListAdapter

viewModel . apply {

itemList . observe ( viewLifecycleOwner , Observer {

pagedListAdapter . submitList ( it )

} )

}

override fun handleLoading ( isLoading : Boolean ) {

// use progress bar

}

https://github.com/dangquanuet/The-Movie-DB-Kotlin/blob/develop/app/src/main/java/com/example/moviedb/ui/base/BasePagedRefreshFragment.kt#L11

Use

PagedMovieAdapter

<span class="token keyword">class</span> <span class="token function">PagedMovieAdapter</span> <span class="token punctuation">(</span>
    <span class="token keyword">val</span> itemClickListener <span class="token operator">:</span> <span class="token punctuation">(</span> Movie <span class="token punctuation">)</span> <span class="token operator">-&gt;</span> Unit <span class="token operator">=</span> <span class="token punctuation">{</span> <span class="token punctuation">}</span>
<span class="token punctuation">)</span> <span class="token operator">:</span> BasePagedListAdapter <span class="token operator">&lt;</span> Movie <span class="token punctuation">,</span> ItemMovieBinding <span class="token operator">&gt;</span> <span class="token punctuation">(</span> <span class="token keyword">object</span> <span class="token operator">:</span> DiffUtil <span class="token punctuation">.</span> ItemCallback <span class="token operator">&lt;</span> Movie <span class="token operator">&gt;</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">override</span> <span class="token keyword">fun</span> <span class="token function">areItemsTheSame</span> <span class="token punctuation">(</span> oldItem <span class="token operator">:</span> Movie <span class="token punctuation">,</span> newItem <span class="token operator">:</span> Movie <span class="token punctuation">)</span> <span class="token operator">:</span> Boolean <span class="token punctuation">{</span>
        <span class="token keyword">return</span> oldItem <span class="token punctuation">.</span> id <span class="token operator">==</span> newItem <span class="token punctuation">.</span> id
    <span class="token punctuation">}</span>

    <span class="token keyword">override</span> <span class="token keyword">fun</span> <span class="token function">areContentsTheSame</span> <span class="token punctuation">(</span> oldItem <span class="token operator">:</span> Movie <span class="token punctuation">,</span> newItem <span class="token operator">:</span> Movie <span class="token punctuation">)</span> <span class="token operator">:</span> Boolean <span class="token punctuation">{</span>
        <span class="token keyword">return</span> oldItem <span class="token operator">==</span> newItem
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span> <span class="token punctuation">)</span> <span class="token punctuation">{</span>

    <span class="token keyword">override</span> <span class="token keyword">fun</span> <span class="token function">getLayoutRes</span> <span class="token punctuation">(</span> viewType <span class="token operator">:</span> Int <span class="token punctuation">)</span> <span class="token operator">:</span> Int <span class="token punctuation">{</span>
        <span class="token keyword">return</span> R <span class="token punctuation">.</span> layout <span class="token punctuation">.</span> item_movie
    <span class="token punctuation">}</span>

    <span class="token keyword">override</span> <span class="token keyword">fun</span> <span class="token function">bindFirstTime</span> <span class="token punctuation">(</span> binding <span class="token operator">:</span> ItemMovieBinding <span class="token punctuation">)</span> <span class="token punctuation">{</span>
        binding <span class="token punctuation">.</span> <span class="token function">apply</span> <span class="token punctuation">{</span>
            root <span class="token punctuation">.</span> <span class="token function">setSingleClick</span> <span class="token punctuation">{</span>
                item <span class="token operator">?</span> <span class="token punctuation">.</span> <span class="token function">apply</span> <span class="token punctuation">{</span>
                    <span class="token function">itemClickListener</span> <span class="token punctuation">(</span> <span class="token keyword">this</span> <span class="token punctuation">)</span>
                <span class="token punctuation">}</span>
            <span class="token punctuation">}</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>

class PagedMovieAdapter (

val itemClickListener : ( Movie ) -> Unit = { }

) : BasePagedListAdapter < Movie , ItemMovieBinding > ( object : DiffUtil . ItemCallback < Movie > ( ) {

override fun areItemsTheSame ( oldItem : Movie , newItem : Movie ) : Boolean {

return oldItem . id == newItem . id

}

override fun areContentsTheSame ( oldItem : Movie , newItem : Movie ) : Boolean {

return oldItem == newItem

}

} ) {

override fun getLayoutRes ( viewType : Int ) : Int {

return R . layout . item_movie

}

override fun bindFirstTime ( binding : ItemMovieBinding ) {

binding . apply {

root . setSingleClick {

item ? . apply {

itemClickListener ( this )

}

https://github.com/dangquanuet/The-Movie-DB-Kotlin/blob/develop/app/src/main/java/com/example/moviedb/ui/screen/paged/PagedMovieAdapter.kt#L10

PagedMovieFragment

<span class="token keyword">class</span> PagedMovieFragment <span class="token operator">:</span>
    BasePagedRefreshFragment <span class="token operator">&lt;</span> FragmentPagedRefreshBinding <span class="token punctuation">,</span> PagedMovieViewModel <span class="token punctuation">,</span> Movie <span class="token operator">&gt;</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span> <span class="token punctuation">{</span>

    <span class="token keyword">override</span> <span class="token keyword">val</span> viewModel <span class="token operator">:</span> PagedMovieViewModel <span class="token keyword">by</span> <span class="token function">viewModel</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span>

    <span class="token keyword">override</span> <span class="token keyword">val</span> pagedListAdapter <span class="token keyword">by</span> lazy <span class="token punctuation">{</span>
        <span class="token function">PagedMovieAdapter</span> <span class="token punctuation">(</span>
            itemClickListener <span class="token operator">=</span> <span class="token punctuation">{</span> <span class="token function">toMovieDetail</span> <span class="token punctuation">(</span> it <span class="token punctuation">)</span> <span class="token punctuation">}</span>
        <span class="token punctuation">)</span>
    <span class="token punctuation">}</span>

    <span class="token keyword">override</span> <span class="token keyword">fun</span> <span class="token function">getLayoutManager</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span> <span class="token operator">=</span> <span class="token function">GridLayoutManager</span> <span class="token punctuation">(</span> context <span class="token punctuation">,</span> <span class="token number">2</span> <span class="token punctuation">)</span>

    <span class="token keyword">override</span> <span class="token keyword">fun</span> <span class="token function">onActivityCreated</span> <span class="token punctuation">(</span> savedInstanceState <span class="token operator">:</span> Bundle <span class="token operator">?</span> <span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">super</span> <span class="token punctuation">.</span> <span class="token function">onActivityCreated</span> <span class="token punctuation">(</span> savedInstanceState <span class="token punctuation">)</span>
        container <span class="token operator">?</span> <span class="token punctuation">.</span> <span class="token function">setBackgroundColor</span> <span class="token punctuation">(</span> Color <span class="token punctuation">.</span> BLACK <span class="token punctuation">)</span>
    <span class="token punctuation">}</span>

    <span class="token keyword">private</span> <span class="token keyword">fun</span> <span class="token function">toMovieDetail</span> <span class="token punctuation">(</span> movie <span class="token operator">:</span> Movie <span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token function">findNavController</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span> <span class="token punctuation">.</span> <span class="token function">navigate</span> <span class="token punctuation">(</span> PagedMovieFragmentDirections <span class="token punctuation">.</span> <span class="token function">toGraphMovieDetail</span> <span class="token punctuation">(</span> movie <span class="token punctuation">)</span> <span class="token punctuation">)</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>

class PagedMovieFragment :

BasePagedRefreshFragment < FragmentPagedRefreshBinding , PagedMovieViewModel , Movie > ( ) {

override val viewModel : PagedMovieViewModel by viewModel ( )

override val pagedListAdapter by lazy {

PagedMovieAdapter (

itemClickListener = { toMovieDetail ( it ) }

)

}

override fun getLayoutManager ( ) = GridLayoutManager ( context , 2 )

container ? . setBackgroundColor ( Color . BLACK )

}

private fun toMovieDetail ( movie : Movie ) {

findNavController ( ) . navigate ( PagedMovieFragmentDirections . toGraphMovieDetail ( movie ) )

}

https://github.com/dangquanuet/The-Movie-DB-Kotlin/blob/develop/app/src/main/java/com/example/moviedb/ui/screen/paged/PagedMovieFragment.kt#L13

PagedMovieViewModel

<span class="token keyword">class</span> <span class="token function">PagedMovieViewModel</span> <span class="token punctuation">(</span>
    <span class="token keyword">private</span> <span class="token keyword">val</span> userRepository <span class="token operator">:</span> UserRepository
<span class="token punctuation">)</span> <span class="token operator">:</span> BasePagedRefreshViewModel <span class="token operator">&lt;</span> Movie <span class="token operator">&gt;</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span> <span class="token punctuation">{</span>

    <span class="token keyword">override</span> <span class="token keyword">suspend</span> <span class="token keyword">fun</span> <span class="token function">loadData</span> <span class="token punctuation">(</span>
        loadInitialParams <span class="token operator">:</span> PageKeyedDataSource <span class="token punctuation">.</span> LoadInitialParams <span class="token operator">&lt;</span> Int <span class="token operator">&gt;</span> <span class="token operator">?</span> <span class="token punctuation">,</span>
        loadParams <span class="token operator">:</span> PageKeyedDataSource <span class="token punctuation">.</span> LoadParams <span class="token operator">&lt;</span> Int <span class="token operator">&gt;</span> <span class="token operator">?</span>
    <span class="token punctuation">)</span> <span class="token operator">:</span> List <span class="token operator">&lt;</span> Movie <span class="token operator">&gt;</span> <span class="token punctuation">{</span>
        <span class="token keyword">val</span> apiParams <span class="token operator">=</span> HashMap <span class="token operator">&lt;</span> String <span class="token punctuation">,</span> String <span class="token operator">&gt;</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span>
        apiParams <span class="token punctuation">[</span> ApiParams <span class="token punctuation">.</span> PAGE <span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token punctuation">(</span> loadParams <span class="token operator">?</span> <span class="token punctuation">.</span> key <span class="token operator">?:</span> firstPage <span class="token punctuation">)</span> <span class="token punctuation">.</span> <span class="token function">toString</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span>

        <span class="token keyword">return</span> userRepository <span class="token punctuation">.</span> <span class="token function">getMovieList</span> <span class="token punctuation">(</span> apiParams <span class="token punctuation">)</span> <span class="token punctuation">.</span> results <span class="token operator">?</span> <span class="token punctuation">.</span> <span class="token function">toList</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span> <span class="token operator">?:</span> <span class="token function">listOf</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span>
    <span class="token punctuation">}</span>

    <span class="token keyword">override</span> <span class="token keyword">val</span> pageSize <span class="token operator">:</span> Int <span class="token operator">=</span> <span class="token number">20</span>

<span class="token punctuation">}</span>

class PagedMovieViewModel (

private val userRepository : UserRepository

) : BasePagedRefreshViewModel < Movie > ( ) {

) : List < Movie > {

val apiParams = HashMap < String , String > ( )

apiParams [ ApiParams . PAGE ] = ( loadParams ? . key ?: firstPage ) . toString ( )

return userRepository . getMovieList ( apiParams ) . results ? . toList ( ) ?: listOf ( )

}

override val pageSize : Int = 20

}

https://github.com/dangquanuet/The-Movie-DB-Kotlin/blob/develop/app/src/main/java/com/example/moviedb/ui/screen/paged/PagedMovieViewModel.kt

Conclusion

You see, with the use of base code, now making screens with more refresh loads become much faster and more convenient, we can easily use for different screens with similar structure.

You can refer to the full source code at ddaay: https://github.com/dangquanuet/The-Movie-DB-Kotlin

See you in the next post .

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Source : Viblo

Building code base for loading more & refresh lists with jetpack paging lib

Preamble

Proceed to the code base

PagedListAdapter

BasePageKeyedDataSource

BasePagedRefreshViewModel

BasePagedRefreshFragment

Use

PagedMovieAdapter

PagedMovieFragment

PagedMovieViewModel

Conclusion

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