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

程序员文章站 2022-05-31 08:17:30

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。

*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

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