摘要:Android AsyncListUtil是Android官方提供的专为列表这样的数据更新加载提供的异步加载组件。基于AsyncListUtil组件,可以轻易实现常见的RecyclerView分页加载技术。AsyncListUtil技术涉及的细节比较繁复,因此我将分别写若干篇文章,分点、分解AsyncListUtil技术。
Android AsyncListUtil是Android官方提供的专为列表这样的数据更新加载提供的异步加载组件。基于AsyncListUtil组件,可以轻易实现常见的RecyclerView分页加载技术。AsyncListUtil技术涉及的细节比较繁复,因此我将分别写若干篇文章,分点、分解AsyncListUtil技术。
先给出一个可运行的例子,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=“调试”; 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(){ //更新数据的元素个数。 //假设预先设定更新若干条。 intcount=Integer.MAX_VALUE; Log.d(TAG,”refreshData:”+count); returncount; } /** *在这里完成数据加载的耗时任务。 * *@paramdata *@paramstartPosition *@paramitemCount */ @Override publicvoidfillData(String[]data,intstartPosition,intitemCount){ Log.d(TAG,”fillData:”+startPosition+“,”+itemCount); for(inti=0;i<itemcount;i++){ · data[i]=String.valueOf(System.currentTimeMillis()); //模拟耗时任务,故意休眠一定时延。 · SystemClock.sleep(100);
}
· }
}
·
privateclassMyViewCallbackextendsAsyncListUtil.ViewCallback{ · /** · *@paramoutRange */ · @Override publicvoidgetItemRangeInto(int[]outRange){ · getOutRange(outRange); · /** *如果当前的RecyclerView为空,主动为用户加载数据. · *假设预先加载若干条数据 * · */ if(outRange[0]==NULL&&outRange[1]==NULL){ · Log.d(TAG,”当前RecyclerView为空!”); outRange[0]=0; · outRange[1]=9; } · Log.d(TAG,”getItemRangeInto,当前可见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=”加载中…”; · } · 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:id=“@+id/button” · android:layout_width=“wrap_content” · android:layout_height=“wrap_content” android:text=“更新”/> · <android.support.v7.widget.recyclerview · · android:id=“@+id/recycler_view” · android:layout_width=“match_parent” · android:layout_height=“match_parent”/> ? <!--?xml version="1.0" encoding="utf-8"?--> <linearlayout android:layout_height="match_parent" android:layout_width="match_parent" android:orientation="vertical" xmlns:android="//schemas.android.com/apk/res/android"><button android:id="@+id/button" android:layout_height="wrap_content" android:layout_width="wrap_content" android:text="更新"> </android.support.v7.widget.recyclerview></button></linearlayout> · (一)new AsyncListUtil之后Android自动就会启动初次刷新加载。原因在AsyncListUtil构造函数里面,已经调用refresh方法启动刷新,见AsyncListUtil构造函数源代码: · /** · *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(); }当代码启动后logcat输出: · 11-2214:41:18.31332764-447/zhangphil.appD/调试:refreshData:2147483647 · 11-2214:41:18.33632764-32764/zhangphil.appD/调试:onDataRefresh:-1,-1 11-2214:41:18.33632764-32764/zhangphil.appD/调试:当前RecyclerView为空! · 11-2214:41:18.33632764-32764/zhangphil.appD/调试:getItemRangeInto,当前可见position:0~9 11-2214:41:18.33732764-449/zhangphil.appD/调试:fillData:0,20 · 11-2214:41:20.35032764-32764/zhangphil.appD/调试:onItemLoaded:0 11-2214:41:20.35132764-32764/zhangphil.appD/调试:onItemLoaded:1 · 11-2214:41:20.35132764-32764/zhangphil.appD/调试:onItemLoaded:2 11-2214:41:20.35232764-32764/zhangphil.appD/调试:onItemLoaded:3 · 11-2214:41:20.35332764-32764/zhangphil.appD/调试:onItemLoaded:4 11-2214:41:20.35332764-32764/zhangphil.appD/调试:onItemLoaded:5 · 11-2214:41:20.35332764-32764/zhangphil.appD/调试:onItemLoaded:6 11-22 14:41:18.313 32764-447/zhangphil.app D/调试: refreshData:2147483647 11-22 14:41:18.336 32764-32764/zhangphil.app D/调试: onDataRefresh:-1,-1 11-22 14:41:18.336 32764-32764/zhangphil.app D/调试: 当前RecyclerView为空! 11-22 14:41:18.336 32764-32764/zhangphil.app D/调试: getItemRangeInto,当前可见position: 0 ~ 9 11-22 14:41:18.337 32764-449/zhangphil.app D/调试: fillData:0,20 11-22 14:41:20.350 32764-32764/zhangphil.app D/调试: onItemLoaded:0 11-22 14:41:20.351 32764-32764/zhangphil.app D/调试: onItemLoaded:1 11-22 14:41:20.351 32764-32764/zhangphil.app D/调试: onItemLoaded:2 11-22 14:41:20.352 32764-32764/zhangphil.app D/调试: onItemLoaded:3 11-22 14:41:20.353 32764-32764/zhangphil.app D/调试: onItemLoaded:4 11-22 14:41:20.353 32764-32764/zhangphil.app D/调试: onItemLoaded:5 11-22 14:41:20.353 32764-32764/zhangphil.app D/调试: onItemLoaded:6
·
(二)在RecyclerView里面的onScrollStateChanged增加onRangeChanged方法,触发AsyncListUtil的关键函数getItemRangeInto。
触发getItemRangeInto的方法有很多种,通常在RecyclerView里面,分页加载常常会由用户的上下翻动RecyclerView触发。因此自然的就想到在RecyclerView的onScrollStateChanged触发AsyncListUtil分页更新加载逻辑。
getItemRangeInto参数outRange维护两个整型元素,前者outRange[0]表示列表顶部可见元素的位置position,后者outRange[1]表示最底部可见元素的position,开发者对这两个值进行计算,通常就是获取当前RecyclerView顶部outRange[0]的FirstVisibleItemPosition,
outRange[1]是LastVisibleItemPosition。当这两个参数赋值后,将直接触发fillData,fillData是AsyncListUtil进行长期耗时后台任务的地方,开发者可以在这里处理自己的后台线程任务。
· 比如现在手指在屏幕上从下往上翻滚RecyclerView,故意翻到没有数据的地方(position=21 ~position=28)然后加载出来,logcat输出:
·
11-2214:42:35.54332764-32764/zhangphil.appD/调试:getItemRangeInto,当前可见position:0~6 · 11-2214:42:36.01232764-32764/zhangphil.appD/调试:onRangeChanged 11-2214:42:36.01232764-32764/zhangphil.appD/调试:getItemRangeInto,当前可见position:5~12 · 11-2214:42:36.01332764-1011/zhangphil.appD/调试:fillData:20,20 11-2214:42:36.84432764-32764/zhangphil.appD/调试:onRangeChanged · 11-2214:42:36.84432764-32764/zhangphil.appD/调试:getItemRangeInto,当前可见position:10~16 11-2214:42:37.06732764-32764/zhangphil.appD/调试:onRangeChanged · 11-2214:42:37.06732764-32764/zhangphil.appD/调试:getItemRangeInto,当前可见position:13~20 11-2214:42:38.02032764-32764/zhangphil.appD/调试:onItemLoaded:20 · 11-2214:42:38.02032764-32764/zhangphil.appD/调试:onItemLoaded:21 11-2214:42:38.02032764-32764/zhangphil.appD/调试:onItemLoaded:22 · 11-2214:42:38.02032764-32764/zhangphil.appD/调试:onItemLoaded:23 11-2214:42:38.02132764-32764/zhangphil.appD/调试:onItemLoaded:24 · 11-2214:42:38.02132764-32764/zhangphil.appD/调试:onItemLoaded:25 11-2214:42:38.02132764-32764/zhangphil.appD/调试:onItemLoaded:26 · 11-2214:42:38.02132764-32764/zhangphil.appD/调试:onItemLoaded:27 11-2214:42:38.02132764-32764/zhangphil.appD/调试:onItemLoaded:28 · 11-2214:42:38.78432764-32764/zhangphil.appD/调试:onRangeChanged 11-2214:42:38.78432764-32764/zhangphil.appD/调试:getItemRangeInto,当前可见position:21~28
(三)fillData分页加载。
fillData将实现最终的分页加载,通常开发者在这里把数据从网络/数据库/文件系统把数据读出来。本例fillData每次读取20条数据,原因是在AsyncListUtil构造时候,指定了tileSize=20。tileSize决定每次分页加载的数据量。由此,每一次AsyncListUtil分页加载的startPosition位置依次是:0,20,40,60……
(四)onItemLoaded数据装载成功后回调。
当fillData把数据加载完成后,会主动的加载到getItemRangeInto所限定的第一个到最后一个可见范围内的item,此时在RecyclerView里面用notifyItemChanged更新UI即可。
(五)fillData加载的数据覆盖getItemRangeInto返回的第一个到最后一个可见范围内的RecyclerView列表项目。
比如,如果getItemRangeInto返回的两个position:outRange[0]=0,outRange[1]=9,那么fillData将一如既往的加载第0个位置开始的20条数据。即fillData的设计目的将为把用户可见区域内容的所有项目数据均加载完成,保证用户可见区域内的数据是优先加载的。
(六)AsyncListUtil的refresh强制刷新。
· /*
· *
Copyright(C)2015TheAndroidOpenSourceProject * · *LicensedundertheApacheLicense,Version2.0(the“License”); *youmaynotusethisfileexceptincompliancewiththeLicense. · *YoumayobtainacopyoftheLicenseat * · *//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. * · * · *Ifthismethodhasbeencalledforaspecificpositionandreturnednull,then · *{@linkViewCallback#onItemLoaded(int)}willbecalledwhenitfinallyloads.Notethatif *thispositionstaysoutsideofthecacheditemrange(asdefinedby · *{@linkViewCallback#extendRangeInto}method),thenthecallbackwillneverbecalledfor *thisposition. · * *@parampositionItemposition. · * *@returnThedataitematthegivenpositionornullifithasnotbeenloaded · *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]){ · · mScrollHint=ViewCallback.HINT_SCROLL_DESC; · }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()){ · · finalintposition=mMissingPositions.keyAt(index); · if(tile.mStartPosition<=position&&position<endposition){ · · mMissingPositions.removeAt(index); · 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++){ · mBackgroundProxy.recycleTile(mTileList.getAtIndex(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|| · (scrollHint==ViewCallback.HINT_SCROLL_DESC))){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.ShouldnotbeaccessedbeyonditemCount. *@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,ifrangeis{100,200}andscrollHint · *is{@link#HINT_SCROLL_ASC},thenoutRangewillbe{50,300}. * · *However,ifscrollHintis{@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); } <code><code><code>/* * 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 * * //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. * </code></code></code> · * 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); } }
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