基於Android官方AsyncListUtil優化改進RecyclerView分頁加載機制(一)。
Android AsyncListUtil是Android官方提供的專為列表這樣的數據更新加載提供的異步加載組件。基於AsyncListUtil組件,可以輕易實現常見的RecyclerView分頁加載技術。AsyncListUtil技術涉及的細節比較繁復,因此我將分別寫若幹篇文章,分點、分解AsyncListUtil技術。
先給出一個可運行的例子,MainActivity.java:
packagezhangphil.app;
importandroid.graphics.Color;
importandroid.os.Bundle;
importandroid.os.SystemClock;
importandroid.support.v7.app.AppCompatActivity;
importandroid.support.v7.util.AsyncListUtil;
importandroid.support.v7.widget.LinearLayoutManager;
importandroid.support.v7.widget.RecyclerView;
importandroid.text.TextUtils;
importandroid.util.Log;
importandroid.view.LayoutInflater;
importandroid.view.View;
importandroid.view.ViewGroup;
importandroid.widget.LinearLayout;
importandroid.widget.TextView;
publicclassMainActivityextendsAppCompatActivity{
privateStringTAG=“調試”;
privatefinalintNULL=-1;
privateRecyclerViewmRecyclerView;
privateAsyncListUtilmAsyncListUtil;
@Override
protectedvoidonCreate(BundlesavedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mRecyclerView=findViewById(R.id.recycler_view);
LinearLayoutManagermLayoutManager=newLinearLayoutManager(this);
mLayoutManager.setOrientation(LinearLayout.VERTICAL);
mRecyclerView.setLayoutManager(mLayoutManager);
RecyclerView.AdaptermAdapter=newMyAdapter();
mRecyclerView.setAdapter(mAdapter);
MyDataCallbackmDataCallback=newMyDataCallback();
MyViewCallbackmViewCallback=newMyViewCallback();
mAsyncListUtil=newAsyncListUtil(String.class,20,mDataCallback,mViewCallback);
mRecyclerView.addOnScrollListener(newRecyclerView.OnScrollListener(){
@Override
publicvoidonScrollStateChanged(RecyclerViewrecyclerView,intnewState){
super.onScrollStateChanged(recyclerView,newState);
Log.d(TAG,”onRangeChanged”);
mAsyncListUtil.onRangeChanged();
}
});
findViewById(R.id.button).setOnClickListener(newView.OnClickListener(){
@Override
publicvoidonClick(Viewv){
Log.d(TAG,”refresh”);
mAsyncListUtil.refresh();
}
});
}
privateclassMyDataCallbackextendsAsyncListUtil.DataCallback{
@Override
publicintrefreshData(){
//更新數據的元素個數。
//假設預先設定更新若幹條。
intcount=Integer.MAX_VALUE;
Log.d(TAG,”refreshData:”+count);
returncount;
}
/**
*在這裡完成數據加載的耗時任務。
*
*@paramdata
*@paramstartPosition
*@paramitemCount
*/
@Override
publicvoidfillData(String[]data,intstartPosition,intitemCount){
Log.d(TAG,”fillData:”+startPosition+“,”+itemCount);
for(inti=0;i<itemcount;i++){
//模擬耗時任務,故意休眠一定時延。
SystemClock.sleep(100);
}
}
}
privateclassMyViewCallbackextendsAsyncListUtil.ViewCallback{
/**
*@paramoutRange
*/
@Override
publicvoidgetItemRangeInto(int[]outRange){
getOutRange(outRange);
/**
*如果當前的RecyclerView為空,主動為用戶加載數據.
*假設預先加載若幹條數據
*
*/
if(outRange[0]==NULL&&outRange[1]==NULL){
Log.d(TAG,”當前RecyclerView為空!”);
outRange[0]=0;
outRange[1]=9;
}
Log.d(TAG,”getItemRangeInto,當前可見position:”+outRange[0]+“~”+outRange[1]);
}
@Override
publicvoidonDataRefresh(){
int[]outRange=newint[2];
getOutRange(outRange);
mRecyclerView.getAdapter().notifyItemRangeChanged(outRange[0],outRange[1]-outRange[0]+1);
Log.d(TAG,”onDataRefresh:”+outRange[0]+“,”+outRange[1]);
}
@Override
publicvoidonItemLoaded(intposition){
mRecyclerView.getAdapter().notifyItemChanged(position);
Log.d(TAG,”onItemLoaded:”+position);
}
}
privatevoidgetOutRange(int[]outRange){
outRange[0]=((LinearLayoutManager)mRecyclerView.getLayoutManager()).findFirstVisibleItemPosition();
outRange[1]=((LinearLayoutManager)mRecyclerView.getLayoutManager()).findLastVisibleItemPosition();
}
privateclassMyAdapterextendsRecyclerView.Adapter{
publicMyAdapter(){
super();
}
@Override
publicViewHolderonCreateViewHolder(ViewGroupviewGroup,inti){
Viewview=LayoutInflater.from(getApplicationContext()).inflate(android.R.layout.simple_list_item_2,null);
ViewHolderholder=newViewHolder(view);
returnholder;
}
@Override
publicvoidonBindViewHolder(ViewHolderviewHolder,inti){
viewHolder.text1.setText(String.valueOf(i));
Strings=String.valueOf(mAsyncListUtil.getItem(i));
if(TextUtils.equals(s,“null”)){
s=”加載中…”;
}
viewHolder.text2.setText(s);
}
@Override
publicintgetItemCount(){
returnmAsyncListUtil.getItemCount();
}
publicclassViewHolderextendsRecyclerView.ViewHolder{
publicTextViewtext1;
publicTextViewtext2;
publicViewHolder(ViewitemView){
super(itemView);
text1=itemView.findViewById(android.R.id.text1);
text1.setTextColor(Color.RED);
text2=itemView.findViewById(android.R.id.text2);
text2.setTextColor(Color.BLUE);
}
}
}
}
android:layout_width=“match_parent”
android:layout_height=“match_parent”
android:orientation=“vertical”>
<button
android:layout_width=“wrap_content”
android:layout_height=“wrap_content”
android:text=“更新”/>
android:id=“@+id/recycler_view”</android.support.v7.widget.recyclerview
android:layout_width=“match_parent”
android:layout_height=“match_parent”/>
(一)new AsyncListUtil之後Android自動就會啟動初次刷新加載。
原因在AsyncListUtil構造函數裡面,已經調用refresh方法啟動刷新,見AsyncListUtil構造函數源代碼:
/**
*CreatesanAsyncListUtil.
*
*@paramklassClassofthedataitem.
*@paramtileSizeNumberofitemperchunkloadedatonce.
*@paramdataCallbackDataaccesscallback.
*@paramviewCallbackCallbackforqueryingvisibleitemrangeandupdatenotifications.
*/
publicAsyncListUtil(Classklass,inttileSize,DataCallbackdataCallback,
ViewCallbackviewCallback){
mTClass=klass;
mTileSize=tileSize;
mDataCallback=dataCallback;
mViewCallback=viewCallback;
mTileList=newTileList(mTileSize);
ThreadUtilthreadUtil=newMessageThreadUtil();
mMainThreadProxy=threadUtil.getMainThreadProxy(mMainThreadCallback);
mBackgroundProxy=threadUtil.getBackgroundProxy(mBackgroundCallback);
refresh();
}
當代碼啟動後logcat輸出:
11-2214:41:18.31332764-447/zhangphil.appD/調試:refreshData:2147483647
11-2214:41:18.33632764-32764/zhangphil.appD/調試:onDataRefresh:-1,-1
11-2214:41:18.33632764-32764/zhangphil.appD/調試:當前RecyclerView為空!
11-2214:41:18.33632764-32764/zhangphil.appD/調試:getItemRangeInto,當前可見position:0~9
11-2214:41:18.33732764-449/zhangphil.appD/調試:fillData:0,20
11-2214:41:20.35032764-32764/zhangphil.appD/調試:onItemLoaded:0
11-2214:41:20.35132764-32764/zhangphil.appD/調試:onItemLoaded:1
11-2214:41:20.35132764-32764/zhangphil.appD/調試:onItemLoaded:2
11-2214:41:20.35232764-32764/zhangphil.appD/調試:onItemLoaded:3
11-2214:41:20.35332764-32764/zhangphil.appD/調試:onItemLoaded:4
11-2214:41:20.35332764-32764/zhangphil.appD/調試:onItemLoaded:5
11-2214:41:20.35332764-32764/zhangphil.appD/調試:onItemLoaded:6
11-22 14:41:18.313 32764-447/zhangphil.app D/調試: refreshData:2147483647 11-22 14:41:18.336 32764-32764/zhangphil.app D/調試: onDataRefresh:-1,-1 11-22 14:41:18.336 32764-32764/zhangphil.app D/調試: 當前RecyclerView為空! 11-22 14:41:18.336 32764-32764/zhangphil.app D/調試: getItemRangeInto,當前可見position: 0 ~ 9 11-22 14:41:18.337 32764-449/zhangphil.app D/調試: fillData:0,20 11-22 14:41:20.350 32764-32764/zhangphil.app D/調試: onItemLoaded:0 11-22 14:41:20.351 32764-32764/zhangphil.app D/調試: onItemLoaded:1 11-22 14:41:20.351 32764-32764/zhangphil.app D/調試: onItemLoaded:2 11-22 14:41:20.352 32764-32764/zhangphil.app D/調試: onItemLoaded:3 11-22 14:41:20.353 32764-32764/zhangphil.app D/調試: onItemLoaded:4 11-22 14:41:20.353 32764-32764/zhangphil.app D/調試: onItemLoaded:5 11-22 14:41:20.353 32764-32764/zhangphil.app D/調試: onItemLoaded:6
(二)在RecyclerView裡面的onScrollStateChanged增加onRangeChanged方法,觸發AsyncListUtil的關鍵函數getItemRangeInto。
觸發getItemRangeInto的方法有很多種,通常在RecyclerView裡面,分頁加載常常會由用戶的上下翻動RecyclerView觸發。因此自然的就想到在RecyclerView的onScrollStateChanged觸發AsyncListUtil分頁更新加載邏輯。
getItemRangeInto參數outRange維護兩個整型元素,前者outRange[0]表示列表頂部可見元素的位置position,後者outRange[1]表示最底部可見元素的position,開發者對這兩個值進行計算,通常就是獲取當前RecyclerView頂部outRange[0]的FirstVisibleItemPosition,
outRange[1]是LastVisibleItemPosition。當這兩個參數賦值後,將直接觸發fillData,fillData是AsyncListUtil進行長期耗時後臺任務的地方,開發者可以在這裡處理自己的後臺線程任務。
比如現在手指在屏幕上從下往上翻滾RecyclerView,故意翻到沒有數據的地方(position=21 ~position=28)然後加載出來,logcat輸出:
11-2214:42:35.54332764-32764/zhangphil.appD/調試:getItemRangeInto,當前可見position:0~6
11-2214:42:36.01232764-32764/zhangphil.appD/調試:onRangeChanged
11-2214:42:36.01232764-32764/zhangphil.appD/調試:getItemRangeInto,當前可見position:5~12
11-2214:42:36.01332764-1011/zhangphil.appD/調試:fillData:20,20
11-2214:42:36.84432764-32764/zhangphil.appD/調試:onRangeChanged
11-2214:42:36.84432764-32764/zhangphil.appD/調試:getItemRangeInto,當前可見position:10~16
11-2214:42:37.06732764-32764/zhangphil.appD/調試:onRangeChanged
11-2214:42:37.06732764-32764/zhangphil.appD/調試:getItemRangeInto,當前可見position:13~20
11-2214:42:38.02032764-32764/zhangphil.appD/調試:onItemLoaded:20
11-2214:42:38.02032764-32764/zhangphil.appD/調試:onItemLoaded:21
11-2214:42:38.02032764-32764/zhangphil.appD/調試:onItemLoaded:22
11-2214:42:38.02032764-32764/zhangphil.appD/調試:onItemLoaded:23
11-2214:42:38.02132764-32764/zhangphil.appD/調試:onItemLoaded:24
11-2214:42:38.02132764-32764/zhangphil.appD/調試:onItemLoaded:25
11-2214:42:38.02132764-32764/zhangphil.appD/調試:onItemLoaded:26
11-2214:42:38.02132764-32764/zhangphil.appD/調試:onItemLoaded:27
11-2214:42:38.02132764-32764/zhangphil.appD/調試:onItemLoaded:28
11-2214:42:38.78432764-32764/zhangphil.appD/調試:onRangeChanged
11-2214:42:38.78432764-32764/zhangphil.appD/調試:getItemRangeInto,當前可見position:21~28
(三)fillData分頁加載。
fillData將實現最終的分頁加載,通常開發者在這裡把數據從網絡/數據庫/文件系統把數據讀出來。本例fillData每次讀取20條數據,原因是在AsyncListUtil構造時候,指定瞭tileSize=20。tileSize決定每次分頁加載的數據量。由此,每一次AsyncListUtil分頁加載的startPosition位置依次是:0,20,40,60……
(四)onItemLoaded數據裝載成功後回調。
當fillData把數據加載完成後,會主動的加載到getItemRangeInto所限定的第一個到最後一個可見范圍內的item,此時在RecyclerView裡面用notifyItemChanged更新UI即可。
(五)fillData加載的數據覆蓋getItemRangeInto返回的第一個到最後一個可見范圍內的RecyclerView列表項目。
比如,如果getItemRangeInto返回的兩個position:outRange[0]=0,outRange[1]=9,那麼fillData將一如既往的加載第0個位置開始的20條數據。即fillData的設計目的將為把用戶可見區域內容的所有項目數據均加載完成,保證用戶可見區域內的數據是優先加載的。
(六)AsyncListUtil的refresh強制刷新。
/*
*Copyright(C)2015TheAndroidOpenSourceProject
*
*LicensedundertheApacheLicense,Version2.0(the“License”);
*youmaynotusethisfileexceptincompliancewiththeLicense.
*YoumayobtainacopyoftheLicenseat
*
*http://www.apache.org/licenses/LICENSE-2.0
*
*Unlessrequiredbyapplicablelaworagreedtoinwriting,software
*distributedundertheLicenseisdistributedonan“ASIS”BASIS,
*WITHOUTWARRANTIESORCONDITIONSOFANYKIND,eitherexpressorimplied.
*SeetheLicenseforthespecificlanguagegoverningpermissionsand
*limitationsundertheLicense.
*/
packageandroid.support.v7.util;
importandroid.support.annotation.UiThread;
importandroid.support.annotation.WorkerThread;
importandroid.util.Log;
importandroid.util.SparseBooleanArray;
importandroid.util.SparseIntArray;
/**
*Autilityclassthatsupportsasynchronouscontentloading.
*
*ItcanbeusedtoloadCursordatainchunkswithoutqueryingtheCursorontheUIThreadwhile
*keepingUIandcachesynchronousforbetteruserexperience.
*
*Itloadsthedataonabackgroundthreadandkeepsonlyalimitednumberoffixedsized
*chunksinmemoryatalltimes.
*
*{@linkAsyncListUtil}queriesthecurrentlyvisiblerangethrough{@linkViewCallback},
*loadstherequireddataitemsinthebackgroundthrough{@linkDataCallback},andnotifiesa
*{@linkViewCallback}whenthedataisloaded.Itmayloadsomeextraitemsforsmoother
*scrolling.
*
*Notethatthisclassusesasinglethreadtoloadthedata,soitsuitabletoloaddatafrom
*secondarystoragesuchasdisk,butnotfromnetwork.
*
*Thisclassisdesignedtoworkwith{@linkandroid.support.v7.widget.RecyclerView},butitdoes
*notdependonitandcanbeusedwithotherlistviews.
*
*/
publicclassAsyncListUtil{
staticfinalStringTAG=“AsyncListUtil”;
staticfinalbooleanDEBUG=false;
finalClassmTClass;
finalintmTileSize;
finalDataCallbackmDataCallback;
finalViewCallbackmViewCallback;
finalTileListmTileList;
finalThreadUtil.MainThreadCallbackmMainThreadProxy;
finalThreadUtil.BackgroundCallbackmBackgroundProxy;
finalint[]mTmpRange=newint[2];
finalint[]mPrevRange=newint[2];
finalint[]mTmpRangeExtended=newint[2];
booleanmAllowScrollHints;
privateintmScrollHint=ViewCallback.HINT_SCROLL_NONE;
intmItemCount=0;
intmDisplayedGeneration=0;
intmRequestedGeneration=mDisplayedGeneration;
finalSparseIntArraymMissingPositions=newSparseIntArray();
voidlog(Strings,Object…args){
Log.d(TAG,”[MAIN]”+String.format(s,args));
}
/**
*CreatesanAsyncListUtil.
*
*@paramklassClassofthedataitem.
*@paramtileSizeNumberofitemperchunkloadedatonce.
*@paramdataCallbackDataaccesscallback.
*@paramviewCallbackCallbackforqueryingvisibleitemrangeandupdatenotifications.
*/
publicAsyncListUtil(Classklass,inttileSize,DataCallbackdataCallback,
ViewCallbackviewCallback){
mTClass=klass;
mTileSize=tileSize;
mDataCallback=dataCallback;
mViewCallback=viewCallback;
mTileList=newTileList(mTileSize);
ThreadUtilthreadUtil=newMessageThreadUtil();
mMainThreadProxy=threadUtil.getMainThreadProxy(mMainThreadCallback);
mBackgroundProxy=threadUtil.getBackgroundProxy(mBackgroundCallback);
refresh();
}
privatebooleanisRefreshPending(){
returnmRequestedGeneration!=mDisplayedGeneration;
}
/**
*Updatesthecurrentlyvisibleitemrange.
*
*
*Identifiesthedataitemsthathavenotbeenloadedyetandinitiatesloadingtheminthe
*background.Shouldbecalledfromtheview’sscrolllistener(suchas
*{@linkandroid.support.v7.widget.RecyclerView.OnScrollListener#onScrolled}).
*/
publicvoidonRangeChanged(){
if(isRefreshPending()){
return;//Willupdaterangewilltherefreshresultarrives.
}
updateRange();
mAllowScrollHints=true;
}
/**
*Forcesreloadingthedata.
*
*Discardsallthecacheddataandreloadsallrequireddataitemsforthecurrentlyvisible
*range.Tobecalledwhenthedataitemcountand/orcontentshaschanged.
*/
publicvoidrefresh(){
mMissingPositions.clear();
mBackgroundProxy.refresh(++mRequestedGeneration);
}
/**
*Returnsthedataitematthegivenpositionornullifithasnotbeenloaded
*yet.
*
*
*Ifthismethodhasbeencalledforaspecificpositionandreturned
null,then
*{@linkViewCallback#onItemLoaded(int)}willbecalledwhenitfinallyloads.Notethatif
*thispositionstaysoutsideofthecacheditemrange(asdefinedby
*{@linkViewCallback#extendRangeInto}method),thenthecallbackwillneverbecalledfor
*thisposition.
*
*@parampositionItemposition.
*
*@returnThedataitematthegivenpositionor
nullifithasnotbeenloaded
*yet.
*/
publicTgetItem(intposition){
if(position<0||position>=mItemCount){
thrownewIndexOutOfBoundsException(position+“isnotwithin0and”+mItemCount);
}
Titem=mTileList.getItemAt(position);
if(item==null&&!isRefreshPending()){
mMissingPositions.put(position,0);
}
returnitem;
}
/**
*Returnsthenumberofitemsinthedataset.
*
*
*Thisisthenumberreturnedbyarecentcallto
*{@linkDataCallback#refreshData()}.
*
*@returnNumberofitems.
*/
publicintgetItemCount(){
returnmItemCount;
}
voidupdateRange(){
mViewCallback.getItemRangeInto(mTmpRange);
if(mTmpRange[0]>mTmpRange[1]||mTmpRange[0]<0){
return;
}
if(mTmpRange[1]>=mItemCount){
//Invalidrangemayarrivesoonaftertherefresh.
return;
}
if(!mAllowScrollHints){
mScrollHint=ViewCallback.HINT_SCROLL_NONE;
}elseif(mTmpRange[0]>mPrevRange[1]||mPrevRange[0]>mTmpRange[1]){
//Rangesdonotintersect,longleapnotascroll.
mScrollHint=ViewCallback.HINT_SCROLL_NONE;
}elseif(mTmpRange[0]<mprevrange[0]){
}elseif(mTmpRange[0]>mPrevRange[0]){
mScrollHint=ViewCallback.HINT_SCROLL_ASC;
}
mPrevRange[0]=mTmpRange[0];
mPrevRange[1]=mTmpRange[1];
mViewCallback.extendRangeInto(mTmpRange,mTmpRangeExtended,mScrollHint);
mTmpRangeExtended[0]=Math.min(mTmpRange[0],Math.max(mTmpRangeExtended[0],0));
mTmpRangeExtended[1]=
Math.max(mTmpRange[1],Math.min(mTmpRangeExtended[1],mItemCount-1));
mBackgroundProxy.updateRange(mTmpRange[0],mTmpRange[1],
mTmpRangeExtended[0],mTmpRangeExtended[1],mScrollHint);
}
privatefinalThreadUtil.MainThreadCallback
mMainThreadCallback=newThreadUtil.MainThreadCallback(){
@Override
publicvoidupdateItemCount(intgeneration,intitemCount){
if(DEBUG){
log(”updateItemCount:size=%d,gen#%d”,itemCount,generation);
}
if(!isRequestedGeneration(generation)){
return;
}
mItemCount=itemCount;
mViewCallback.onDataRefresh();
mDisplayedGeneration=mRequestedGeneration;
recycleAllTiles();
mAllowScrollHints=false;//Willbesettotrueafterafirstrealscroll.
//Therewillbenoscrolleventifthesizechangedoesnotaffectthecurrentrange.
updateRange();
}
@Override
publicvoidaddTile(intgeneration,TileList.Tiletile){
if(!isRequestedGeneration(generation)){
if(DEBUG){
log(”recyclinganoldergenerationtile@%d”,tile.mStartPosition);
}
mBackgroundProxy.recycleTile(tile);
return;
}
TileList.Tileduplicate=mTileList.addOrReplace(tile);
if(duplicate!=null){
Log.e(TAG,”duplicatetile@”+duplicate.mStartPosition);
mBackgroundProxy.recycleTile(duplicate);
}
if(DEBUG){
log(”gen#%d,addedtile@%d,totaltiles:%d”,
generation,tile.mStartPosition,mTileList.size());
}
intendPosition=tile.mStartPosition+tile.mItemCount;
intindex=0;
while(index<mmissingpositions.size()){
if(tile.mStartPosition<=position&&position<endposition){
mViewCallback.onItemLoaded(position);
}else{
index++;
}
}
}
@Override
publicvoidremoveTile(intgeneration,intposition){
if(!isRequestedGeneration(generation)){
return;
}
TileList.Tiletile=mTileList.removeAtPos(position);
if(tile==null){
Log.e(TAG,”tilenotfound@”+position);
return;
}
if(DEBUG){
log(”recyclingtile@%d,totaltiles:%d”,tile.mStartPosition,mTileList.size());
}
mBackgroundProxy.recycleTile(tile);
}
privatevoidrecycleAllTiles(){
if(DEBUG){
log(”recyclingall%dtiles”,mTileList.size());
}
for(inti=0;i<mtilelist.size();i++){
}
mTileList.clear();
}
privatebooleanisRequestedGeneration(intgeneration){
returngeneration==mRequestedGeneration;
}
};
privatefinalThreadUtil.BackgroundCallback
mBackgroundCallback=newThreadUtil.BackgroundCallback(){
privateTileList.TilemRecycledRoot;
finalSparseBooleanArraymLoadedTiles=newSparseBooleanArray();
privateintmGeneration;
privateintmItemCount;
privateintmFirstRequiredTileStart;
privateintmLastRequiredTileStart;
@Override
publicvoidrefresh(intgeneration){
mGeneration=generation;
mLoadedTiles.clear();
mItemCount=mDataCallback.refreshData();
mMainThreadProxy.updateItemCount(mGeneration,mItemCount);
}
@Override
publicvoidupdateRange(intrangeStart,intrangeEnd,intextRangeStart,intextRangeEnd,
intscrollHint){
if(DEBUG){
log(”updateRange:%d..%dextendedto%d..%d,scrollhint:%d”,
rangeStart,rangeEnd,extRangeStart,extRangeEnd,scrollHint);
}
if(rangeStart>rangeEnd){
return;
}
finalintfirstVisibleTileStart=getTileStart(rangeStart);
finalintlastVisibleTileStart=getTileStart(rangeEnd);
mFirstRequiredTileStart=getTileStart(extRangeStart);
mLastRequiredTileStart=getTileStart(extRangeEnd);
if(DEBUG){
log(”requestingtilerange:%d..%d”,
mFirstRequiredTileStart,mLastRequiredTileStart);
}
//AllpendingtilerequestsareremovedbyThreadUtilatthispoint.
//Re-requestallrequiredtilesinthemostoptimalorder.
if(scrollHint==ViewCallback.HINT_SCROLL_DESC){
requestTiles(mFirstRequiredTileStart,lastVisibleTileStart,scrollHint,true);
requestTiles(lastVisibleTileStart+mTileSize,mLastRequiredTileStart,scrollHint,
false);
}else{
requestTiles(firstVisibleTileStart,mLastRequiredTileStart,scrollHint,false);
requestTiles(mFirstRequiredTileStart,firstVisibleTileStart-mTileSize,scrollHint,
true);
}
}
privateintgetTileStart(intposition){
returnposition-position%mTileSize;
}
privatevoidrequestTiles(intfirstTileStart,intlastTileStart,intscrollHint,
booleanbackwards){
for(inti=firstTileStart;i<=lastTileStart;i+=mTileSize){
inttileStart=backwards?(lastTileStart+firstTileStart-i):i;
if(DEBUG){
log(”requestingtile@%d”,tileStart);
}
mBackgroundProxy.loadTile(tileStart,scrollHint);
}
}
@Override
publicvoidloadTile(intposition,intscrollHint){
if(isTileLoaded(position)){
if(DEBUG){
log(”alreadyloadedtile@%d”,position);
}
return;
}
TileList.Tiletile=acquireTile();
tile.mStartPosition=position;
tile.mItemCount=Math.min(mTileSize,mItemCount-tile.mStartPosition);
mDataCallback.fillData(tile.mItems,tile.mStartPosition,tile.mItemCount);
flushTileCache(scrollHint);
addTile(tile);
}
@Override
publicvoidrecycleTile(TileList.Tiletile){
if(DEBUG){
log(”recyclingtile@%d”,tile.mStartPosition);
}
mDataCallback.recycleData(tile.mItems,tile.mItemCount);
tile.mNext=mRecycledRoot;
mRecycledRoot=tile;
}
privateTileList.TileacquireTile(){
if(mRecycledRoot!=null){
TileList.Tileresult=mRecycledRoot;
mRecycledRoot=mRecycledRoot.mNext;
returnresult;
}
returnnewTileList.Tile(mTClass,mTileSize);
}
privatebooleanisTileLoaded(intposition){
returnmLoadedTiles.get(position);
}
privatevoidaddTile(TileList.Tiletile){
mLoadedTiles.put(tile.mStartPosition,true);
mMainThreadProxy.addTile(mGeneration,tile);
if(DEBUG){
log(”loadedtile@%d,totaltiles:%d”,tile.mStartPosition,mLoadedTiles.size());
}
}
privatevoidremoveTile(intposition){
mLoadedTiles.delete(position);
mMainThreadProxy.removeTile(mGeneration,position);
if(DEBUG){
log(”flushedtile@%d,totaltiles:%s”,position,mLoadedTiles.size());
}
}
privatevoidflushTileCache(intscrollHint){
finalintcacheSizeLimit=mDataCallback.getMaxCachedTiles();
while(mLoadedTiles.size()>=cacheSizeLimit){
intfirstLoadedTileStart=mLoadedTiles.keyAt(0);
intlastLoadedTileStart=mLoadedTiles.keyAt(mLoadedTiles.size()-1);
intstartMargin=mFirstRequiredTileStart-firstLoadedTileStart;
intendMargin=lastLoadedTileStart-mLastRequiredTileStart;
if(startMargin>0&&(startMargin>=endMargin||
(scrollHint==ViewCallback.HINT_SCROLL_ASC))){
removeTile(firstLoadedTileStart);
}elseif(endMargin>0&&(startMargin<endmargin||
removeTile(lastLoadedTileStart);
}else{
//Couldnotflushoneitherside,bailout.
return;
}
}
}
privatevoidlog(Strings,Object…args){
Log.d(TAG,”[BKGR]”+String.format(s,args));
}
};
/**
*Thecallbackthatprovidesdataaccessfor{@linkAsyncListUtil}.
*
*
*Allmethodsarecalledonthebackgroundthread.
*/
publicstaticabstractclassDataCallback{
/**
*Refreshthedatasetandreturnthenewdataitemcount.
*
*
*Ifthedataisbeingaccessedthrough{@linkandroid.database.Cursor}thisiswhere
*thenewcursorshouldbecreated.
*
*@returnDataitemcount.
*/
@WorkerThread
publicabstractintrefreshData();
/**
*Fillthegiventile.
*
*
*Theprovidedtilemightbearecycledtile,inwhichcaseitwillalreadyhaveobjects.
*Itissuggestedtore-usetheseobjectsifpossibleinyourusecase.
*
*@paramstartPositionThestartpositioninthelist.
*@paramitemCountThedataitemcount.
*@paramdataThedataitemarraytofillinto.Shouldnotbeaccessedbeyond
*
itemCount.
*/
@WorkerThread
publicabstractvoidfillData(T[]data,intstartPosition,intitemCount);
/**
*Recycletheobjectscreatedin{@link#fillData}ifnecessary.
*
*
*@paramdataArrayofdataitems.Shouldnotbeaccessedbeyond
itemCount.
*@paramitemCountThedataitemcount.
*/
@WorkerThread
publicvoidrecycleData(T[]data,intitemCount){
}
/**
*Returnstilecachesizelimit(intiles).
*
*
*Theactualnumberofcachedtileswillbethemaximumofthisvalueandthenumberof
*tilesthatisrequiredtocovertherangereturnedby
*{@linkViewCallback#extendRangeInto(int[],int[],int)}.
*
*Forexample,ifthismethodreturns10,andthemost
*recentcallto{@linkViewCallback#extendRangeInto(int[],int[],int)}returned
*{100,179},andthetilesizeis5,thenthemaximumnumberofcachedtileswillbe16.
*
*However,ifthetilesizeis20,thenthemaximumnumberofcachedtileswillbe10.
*
*Thedefaultimplementationreturns10.
*
*@returnMaximumcachesize.
*/
@WorkerThread
publicintgetMaxCachedTiles(){
return10;
}
}
/**
*Thecallbackthatlinks{@linkAsyncListUtil}withthelistview.
*
*
*Allmethodsarecalledonthemainthread.
*/
publicstaticabstractclassViewCallback{
/**
*Noscrolldirectionhintavailable.
*/
publicstaticfinalintHINT_SCROLL_NONE=0;
/**
*Scrollingindescendingorder(fromhighertolowerpositionsintheorderofthebacking
*storage).
*/
publicstaticfinalintHINT_SCROLL_DESC=1;
/**
*Scrollinginascendingorder(fromlowertohigherpositionsintheorderofthebacking
*storage).
*/
publicstaticfinalintHINT_SCROLL_ASC=2;
/**
*Computetherangeofvisibleitempositions.
*
*outRange[0]isthepositionofthefirstvisibleitem(intheorderofthebacking
*storage).
*
*outRange[1]isthepositionofthelastvisibleitem(intheorderofthebacking
*storage).
*
*Negativepositionsandpositionsgreaterorequalto{@link#getItemCount}areinvalid.
*Ifthereturnedrangecontainsinvalidpositionsitisignored(noitemwillbeloaded).
*
*@paramoutRangeThevisibleitemrange.
*/
@UiThread
publicabstractvoidgetItemRangeInto(int[]outRange);
/**
*Computeawiderrangeofitemsthatwillbeloadedforsmootherscrolling.
*
*
*Ifthereisnoscrollhint,thedefaultimplementationextendsthevisiblerangebyhalf
*itslengthinbothdirections.Ifthereisascrollhint,therangeisextendedby
*itsfulllengthinthescrolldirection,andbyhalfintheotherdirection.
*
*Forexample,if
rangeis
{100,200}and
scrollHint
*is{@link#HINT_SCROLL_ASC},then
outRangewillbe
{50,300}.
*
*However,if
scrollHintis{@link#HINT_SCROLL_NONE},then
*
outRangewillbe
{50,250}
*
*@paramrangeVisibleitemrange.
*@paramoutRangeExtendedrange.
*@paramscrollHintThescrolldirectionhint.
*/
@UiThread
publicvoidextendRangeInto(int[]range,int[]outRange,intscrollHint){
finalintfullRange=range[1]-range[0]+1;
finalinthalfRange=fullRange/2;
outRange[0]=range[0]-(scrollHint==HINT_SCROLL_DESC?fullRange:halfRange);
outRange[1]=range[1]+(scrollHint==HINT_SCROLL_ASC?fullRange:halfRange);
}
/**
*Calledwhentheentiredatasethaschanged.
*/
@UiThread
publicabstractvoidonDataRefresh();
/**
*Calledwhenanitematthegivenpositionisloaded.
*@parampositionItemposition.
*/
@UiThread
publicabstractvoidonItemLoaded(intposition);
}
}
/*
* Copyright (C) 2015 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package android.support.v7.util;
import android.support.annotation.UiThread;
import android.support.annotation.WorkerThread;
import android.util.Log;
import android.util.SparseBooleanArray;
import android.util.SparseIntArray;
/**
* A utility class that supports asynchronous content loading.
*
* It can be used to load Cursor data in chunks without querying the Cursor on the UI Thread while * keeping UI and cache synchronous for better user experience. *
* It loads the data on a background thread and keeps only a limited number of fixed sized * chunks in memory at all times. *
* {@link AsyncListUtil} queries the currently visible range through {@link ViewCallback}, * loads the required data items in the background through {@link DataCallback}, and notifies a * {@link ViewCallback} when the data is loaded. It may load some extra items for smoother * scrolling. *
* Note that this class uses a single thread to load the data, so it suitable to load data from * secondary storage such as disk, but not from network. *
* This class is designed to work with {@link android.support.v7.widget.RecyclerView}, but it does * not depend on it and can be used with other list views. * */ public class AsyncListUtil { static final String TAG = "AsyncListUtil"; static final boolean DEBUG = false; final Class mTClass; final int mTileSize; final DataCallback mDataCallback; final ViewCallback mViewCallback; final TileList mTileList; final ThreadUtil.MainThreadCallback mMainThreadProxy; final ThreadUtil.BackgroundCallback mBackgroundProxy; final int[] mTmpRange = new int[2]; final int[] mPrevRange = new int[2]; final int[] mTmpRangeExtended = new int[2]; boolean mAllowScrollHints; private int mScrollHint = ViewCallback.HINT_SCROLL_NONE; int mItemCount = 0; int mDisplayedGeneration = 0; int mRequestedGeneration = mDisplayedGeneration; final SparseIntArray mMissingPositions = new SparseIntArray(); void log(String s, Object... args) { Log.d(TAG, "[MAIN] " + String.format(s, args)); } /** * Creates an AsyncListUtil. * * @param klass Class of the data item. * @param tileSize Number of item per chunk loaded at once. * @param dataCallback Data access callback. * @param viewCallback Callback for querying visible item range and update notifications. */ public AsyncListUtil(Class klass, int tileSize, DataCallback dataCallback, ViewCallback viewCallback) { mTClass = klass; mTileSize = tileSize; mDataCallback = dataCallback; mViewCallback = viewCallback; mTileList = new TileList(mTileSize); ThreadUtil threadUtil = new MessageThreadUtil(); mMainThreadProxy = threadUtil.getMainThreadProxy(mMainThreadCallback); mBackgroundProxy = threadUtil.getBackgroundProxy(mBackgroundCallback); refresh(); } private boolean isRefreshPending() { return mRequestedGeneration != mDisplayedGeneration; } /** * Updates the currently visible item range. * *
* Identifies the data items that have not been loaded yet and initiates loading them in the * background. Should be called from the view's scroll listener (such as * {@link android.support.v7.widget.RecyclerView.OnScrollListener#onScrolled}). */ public void onRangeChanged() { if (isRefreshPending()) { return; // Will update range will the refresh result arrives. } updateRange(); mAllowScrollHints = true; } /** * Forces reloading the data. *
* Discards all the cached data and reloads all required data items for the currently visible * range. To be called when the data item count and/or contents has changed. */ public void refresh() { mMissingPositions.clear(); mBackgroundProxy.refresh(++mRequestedGeneration); } /** * Returns the data item at the given position or
null if it has not been loaded * yet. * *
* If this method has been called for a specific position and returned
null, then * {@link ViewCallback#onItemLoaded(int)} will be called when it finally loads. Note that if * this position stays outside of the cached item range (as defined by * {@link ViewCallback#extendRangeInto} method), then the callback will never be called for * this position. * * @param position Item position. * * @return The data item at the given position or
null if it has not been loaded * yet. */ public T getItem(int position) { if (position < 0 || position >= mItemCount) { throw new IndexOutOfBoundsException(position + " is not within 0 and " + mItemCount); } T item = mTileList.getItemAt(position); if (item == null && !isRefreshPending()) { mMissingPositions.put(position, 0); } return item; } /** * Returns the number of items in the data set. * *
* This is the number returned by a recent call to * {@link DataCallback#refreshData()}. * * @return Number of items. */ public int getItemCount() { return mItemCount; } void updateRange() { mViewCallback.getItemRangeInto(mTmpRange); if (mTmpRange[0] > mTmpRange[1] || mTmpRange[0] < 0) { return; } if (mTmpRange[1] >= mItemCount) { // Invalid range may arrive soon after the refresh. return; } if (!mAllowScrollHints) { mScrollHint = ViewCallback.HINT_SCROLL_NONE; } else if (mTmpRange[0] > mPrevRange[1] || mPrevRange[0] > mTmpRange[1]) { // Ranges do not intersect, long leap not a scroll. mScrollHint = ViewCallback.HINT_SCROLL_NONE; } else if (mTmpRange[0] < mPrevRange[0]) { mScrollHint = ViewCallback.HINT_SCROLL_DESC; } else if (mTmpRange[0] > mPrevRange[0]) { mScrollHint = ViewCallback.HINT_SCROLL_ASC; } mPrevRange[0] = mTmpRange[0]; mPrevRange[1] = mTmpRange[1]; mViewCallback.extendRangeInto(mTmpRange, mTmpRangeExtended, mScrollHint); mTmpRangeExtended[0] = Math.min(mTmpRange[0], Math.max(mTmpRangeExtended[0], 0)); mTmpRangeExtended[1] = Math.max(mTmpRange[1], Math.min(mTmpRangeExtended[1], mItemCount - 1)); mBackgroundProxy.updateRange(mTmpRange[0], mTmpRange[1], mTmpRangeExtended[0], mTmpRangeExtended[1], mScrollHint); } private final ThreadUtil.MainThreadCallback mMainThreadCallback = new ThreadUtil.MainThreadCallback() { @Override public void updateItemCount(int generation, int itemCount) { if (DEBUG) { log("updateItemCount: size=%d, gen #%d", itemCount, generation); } if (!isRequestedGeneration(generation)) { return; } mItemCount = itemCount; mViewCallback.onDataRefresh(); mDisplayedGeneration = mRequestedGeneration; recycleAllTiles(); mAllowScrollHints = false; // Will be set to true after a first real scroll. // There will be no scroll event if the size change does not affect the current range. updateRange(); } @Override public void addTile(int generation, TileList.Tile tile) { if (!isRequestedGeneration(generation)) { if (DEBUG) { log("recycling an older generation tile @%d", tile.mStartPosition); } mBackgroundProxy.recycleTile(tile); return; } TileList.Tile duplicate = mTileList.addOrReplace(tile); if (duplicate != null) { Log.e(TAG, "duplicate tile @" + duplicate.mStartPosition); mBackgroundProxy.recycleTile(duplicate); } if (DEBUG) { log("gen #%d, added tile @%d, total tiles: %d", generation, tile.mStartPosition, mTileList.size()); } int endPosition = tile.mStartPosition + tile.mItemCount; int index = 0; while (index < mMissingPositions.size()) { final int position = mMissingPositions.keyAt(index); if (tile.mStartPosition <= position && position < endPosition) { mMissingPositions.removeAt(index); mViewCallback.onItemLoaded(position); } else { index++; } } } @Override public void removeTile(int generation, int position) { if (!isRequestedGeneration(generation)) { return; } TileList.Tile tile = mTileList.removeAtPos(position); if (tile == null) { Log.e(TAG, "tile not found @" + position); return; } if (DEBUG) { log("recycling tile @%d, total tiles: %d", tile.mStartPosition, mTileList.size()); } mBackgroundProxy.recycleTile(tile); } private void recycleAllTiles() { if (DEBUG) { log("recycling all %d tiles", mTileList.size()); } for (int i = 0; i < mTileList.size(); i++) { mBackgroundProxy.recycleTile(mTileList.getAtIndex(i)); } mTileList.clear(); } private boolean isRequestedGeneration(int generation) { return generation == mRequestedGeneration; } }; private final ThreadUtil.BackgroundCallback mBackgroundCallback = new ThreadUtil.BackgroundCallback() { private TileList.Tile mRecycledRoot; final SparseBooleanArray mLoadedTiles = new SparseBooleanArray(); private int mGeneration; private int mItemCount; private int mFirstRequiredTileStart; private int mLastRequiredTileStart; @Override public void refresh(int generation) { mGeneration = generation; mLoadedTiles.clear(); mItemCount = mDataCallback.refreshData(); mMainThreadProxy.updateItemCount(mGeneration, mItemCount); } @Override public void updateRange(int rangeStart, int rangeEnd, int extRangeStart, int extRangeEnd, int scrollHint) { if (DEBUG) { log("updateRange: %d..%d extended to %d..%d, scroll hint: %d", rangeStart, rangeEnd, extRangeStart, extRangeEnd, scrollHint); } if (rangeStart > rangeEnd) { return; } final int firstVisibleTileStart = getTileStart(rangeStart); final int lastVisibleTileStart = getTileStart(rangeEnd); mFirstRequiredTileStart = getTileStart(extRangeStart); mLastRequiredTileStart = getTileStart(extRangeEnd); if (DEBUG) { log("requesting tile range: %d..%d", mFirstRequiredTileStart, mLastRequiredTileStart); } // All pending tile requests are removed by ThreadUtil at this point. // Re-request all required tiles in the most optimal order. if (scrollHint == ViewCallback.HINT_SCROLL_DESC) { requestTiles(mFirstRequiredTileStart, lastVisibleTileStart, scrollHint, true); requestTiles(lastVisibleTileStart + mTileSize, mLastRequiredTileStart, scrollHint, false); } else { requestTiles(firstVisibleTileStart, mLastRequiredTileStart, scrollHint, false); requestTiles(mFirstRequiredTileStart, firstVisibleTileStart - mTileSize, scrollHint, true); } } private int getTileStart(int position) { return position - position % mTileSize; } private void requestTiles(int firstTileStart, int lastTileStart, int scrollHint, boolean backwards) { for (int i = firstTileStart; i <= lastTileStart; i += mTileSize) { int tileStart = backwards ? (lastTileStart + firstTileStart - i) : i; if (DEBUG) { log("requesting tile @%d", tileStart); } mBackgroundProxy.loadTile(tileStart, scrollHint); } } @Override public void loadTile(int position, int scrollHint) { if (isTileLoaded(position)) { if (DEBUG) { log("already loaded tile @%d", position); } return; } TileList.Tile tile = acquireTile(); tile.mStartPosition = position; tile.mItemCount = Math.min(mTileSize, mItemCount - tile.mStartPosition); mDataCallback.fillData(tile.mItems, tile.mStartPosition, tile.mItemCount); flushTileCache(scrollHint); addTile(tile); } @Override public void recycleTile(TileList.Tile tile) { if (DEBUG) { log("recycling tile @%d", tile.mStartPosition); } mDataCallback.recycleData(tile.mItems, tile.mItemCount); tile.mNext = mRecycledRoot; mRecycledRoot = tile; } private TileList.Tile acquireTile() { if (mRecycledRoot != null) { TileList.Tile result = mRecycledRoot; mRecycledRoot = mRecycledRoot.mNext; return result; } return new TileList.Tile(mTClass, mTileSize); } private boolean isTileLoaded(int position) { return mLoadedTiles.get(position); } private void addTile(TileList.Tile tile) { mLoadedTiles.put(tile.mStartPosition, true); mMainThreadProxy.addTile(mGeneration, tile); if (DEBUG) { log("loaded tile @%d, total tiles: %d", tile.mStartPosition, mLoadedTiles.size()); } } private void removeTile(int position) { mLoadedTiles.delete(position); mMainThreadProxy.removeTile(mGeneration, position); if (DEBUG) { log("flushed tile @%d, total tiles: %s", position, mLoadedTiles.size()); } } private void flushTileCache(int scrollHint) { final int cacheSizeLimit = mDataCallback.getMaxCachedTiles(); while (mLoadedTiles.size() >= cacheSizeLimit) { int firstLoadedTileStart = mLoadedTiles.keyAt(0); int lastLoadedTileStart = mLoadedTiles.keyAt(mLoadedTiles.size() - 1); int startMargin = mFirstRequiredTileStart - firstLoadedTileStart; int endMargin = lastLoadedTileStart - mLastRequiredTileStart; if (startMargin > 0 && (startMargin >= endMargin || (scrollHint == ViewCallback.HINT_SCROLL_ASC))) { removeTile(firstLoadedTileStart); } else if (endMargin > 0 && (startMargin < endMargin || (scrollHint == ViewCallback.HINT_SCROLL_DESC))){ removeTile(lastLoadedTileStart); } else { // Could not flush on either side, bail out. return; } } } private void log(String s, Object... args) { Log.d(TAG, "[BKGR] " + String.format(s, args)); } }; /** * The callback that provides data access for {@link AsyncListUtil}. * *
* All methods are called on the background thread. */ public static abstract class DataCallback { /** * Refresh the data set and return the new data item count. * *
* If the data is being accessed through {@link android.database.Cursor} this is where * the new cursor should be created. * * @return Data item count. */ @WorkerThread public abstract int refreshData(); /** * Fill the given tile. * *
* The provided tile might be a recycled tile, in which case it will already have objects. * It is suggested to re-use these objects if possible in your use case. * * @param startPosition The start position in the list. * @param itemCount The data item count. * @param data The data item array to fill into. Should not be accessed beyond *
itemCount. */ @WorkerThread public abstract void fillData(T[] data, int startPosition, int itemCount); /** * Recycle the objects created in {@link #fillData} if necessary. * * * @param data Array of data items. Should not be accessed beyond
itemCount. * @param itemCount The data item count. */ @WorkerThread public void recycleData(T[] data, int itemCount) { } /** * Returns tile cache size limit (in tiles). * *
* The actual number of cached tiles will be the maximum of this value and the number of * tiles that is required to cover the range returned by * {@link ViewCallback#extendRangeInto(int[], int[], int)}. *
* For example, if this method returns 10, and the most * recent call to {@link ViewCallback#extendRangeInto(int[], int[], int)} returned * {100, 179}, and the tile size is 5, then the maximum number of cached tiles will be 16. *
* However, if the tile size is 20, then the maximum number of cached tiles will be 10. *
* The default implementation returns 10. * * @return Maximum cache size. */ @WorkerThread public int getMaxCachedTiles() { return 10; } } /** * The callback that links {@link AsyncListUtil} with the list view. * *
* All methods are called on the main thread. */ public static abstract class ViewCallback { /** * No scroll direction hint available. */ public static final int HINT_SCROLL_NONE = 0; /** * Scrolling in descending order (from higher to lower positions in the order of the backing * storage). */ public static final int HINT_SCROLL_DESC = 1; /** * Scrolling in ascending order (from lower to higher positions in the order of the backing * storage). */ public static final int HINT_SCROLL_ASC = 2; /** * Compute the range of visible item positions. *
* outRange[0] is the position of the first visible item (in the order of the backing * storage). *
* outRange[1] is the position of the last visible item (in the order of the backing * storage). *
* Negative positions and positions greater or equal to {@link #getItemCount} are invalid. * If the returned range contains invalid positions it is ignored (no item will be loaded). * * @param outRange The visible item range. */ @UiThread public abstract void getItemRangeInto(int[] outRange); /** * Compute a wider range of items that will be loaded for smoother scrolling. * *
* If there is no scroll hint, the default implementation extends the visible range by half * its length in both directions. If there is a scroll hint, the range is extended by * its full length in the scroll direction, and by half in the other direction. *
* For example, if
range is
{100, 200} and
scrollHint * is {@link #HINT_SCROLL_ASC}, then
outRange will be
{50, 300}. *
* However, if
scrollHint is {@link #HINT_SCROLL_NONE}, then *
outRange will be
{50, 250} * * @param range Visible item range. * @param outRange Extended range. * @param scrollHint The scroll direction hint. */ @UiThread public void extendRangeInto(int[] range, int[] outRange, int scrollHint) { final int fullRange = range[1] - range[0] + 1; final int halfRange = fullRange / 2; outRange[0] = range[0] - (scrollHint == HINT_SCROLL_DESC ? fullRange : halfRange); outRange[1] = range[1] + (scrollHint == HINT_SCROLL_ASC ? fullRange : halfRange); } /** * Called when the entire data set has changed. */ @UiThread public abstract void onDataRefresh(); /** * Called when an item at the given position is loaded. * @param position Item position. */ @UiThread public abstract void onItemLoaded(int position); } }