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基于Android官方AsyncListUtil优化改进RecyclerView分页加载机制(一)

程序员文章站 2023-01-29 21:08:31
基于android官方asynclistutil优化改进recyclerview分页加载机制(一)。 android asynclistutil是android官方提供的专为...

基于android官方asynclistutil优化改进recyclerview分页加载机制(一)。

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。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
  • 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”
    =“http:>
    android:layout_height=“match_parent”

    android:orientation=“vertical”>



  • android:id=“@+id/button”
  • android:layout_width=“wrap_content”

    android:layout_height=“wrap_content”

    android:text=“更新”/>



  • android:id=“@+id/recycler_view”
  • android:layout_width=“match_parent”

    android:layout_height=“match_parent”/>
    
    
    
        
    
    



    (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//文件把数据读出来。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

    *

    *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.

    *

    *

     

    *ifthismethodhasbeencalledforecificpositionandreturnednull,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]

  • 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

  • finalintposition=mmissingpositions.keyat(index);
  • if(tile.mstartposition<=position&&position

  • 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
  • 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
  • (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-usethebjectsifpossibleinyourusecase.

    *

    *@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);

    }

    }
    /*
     * 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, extrang