使用CursorLoader异步加载数据
Android3.0引入了CursorLoader实现异步加载数据，为了避免同步查询数据库时阻塞UI线程的问题。在API11之前可以通过下载支持库，来使之前的系统支持此功能。
下面是一个例子：
publicclassListViewLoaderextendsListActivity implementsLoaderManager.LoaderCallbacks{ //ThisistheAdapterbeingusedtodisplaythelist'sdata SimpleCursorAdaptermAdapter; //ThesearetheContactsrowsthatwewillretrieve staticfinalString[]PROJECTION=newString[]{ContactsContract.Data._ID, ContactsContract.Data.DISPLAY_NAME}; //Thisistheselectcriteria staticfinalStringSELECTION="(("+ ContactsContract.Data.DISPLAY_NAME+"NOTNULL)AND("+ ContactsContract.Data.DISPLAY_NAME+"!=''))"; @Override protectedvoidonCreate(BundlesavedInstanceState){ super.onCreate(savedInstanceState); //Createaprogressbartodisplaywhilethelistloads ProgressBarprogressBar=newProgressBar(this); progressBar.setLayoutParams(newLayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT,Gravity.CENTER)); progressBar.setIndeterminate(true); getListView().setEmptyView(progressBar); //Mustaddtheprogressbartotherootofthelayout ViewGrouproot=(ViewGroup)findViewById(android.R.id.content); root.addView(progressBar); //Forthecursoradapter,specifywhichcolumnsgointowhichviews String[]fromColumns={ContactsContract.Data.DISPLAY_NAME}; int[]toViews={android.R.id.text1};//TheTextViewinsimple_list_item_1 //Createanemptyadapterwewillusetodisplaytheloadeddata. //Wepassnullforthecursor,thenupdateitinonLoadFinished() mAdapter=newSimpleCursorAdapter(this, android.R.layout.simple_list_item_1,null, fromColumns,toViews,0); setListAdapter(mAdapter); //Preparetheloader.Eitherre-connectwithanexistingone, //orstartanewone. getLoaderManager().initLoader(0,null,this); } //CalledwhenanewLoaderneedstobecreated publicLoader onCreateLoader(intid,Bundleargs){ //NowcreateandreturnaCursorLoaderthatwilltakecareof //creatingaCursorforthedatabeingdisplayed. returnnewCursorLoader(this,ContactsContract.Data.CONTENT_URI, PROJECTION,SELECTION,null,null); } //Calledwhenapreviouslycreatedloaderhasfinishedloading publicvoidonLoadFinished(Loader loader,Cursordata){ //Swapthenewcursorin.(Theframeworkwilltakecareofclosingthe //oldcursoroncewereturn.) mAdapter.swapCursor(data); } //Calledwhenapreviouslycreatedloaderisreset,makingthedataunavailable publicvoidonLoaderReset(Loader loader){ //ThisiscalledwhenthelastCursorprovidedtoonLoadFinished() //aboveisabouttobeclosed.Weneedtomakesureweareno //longerusingit. mAdapter.swapCursor(null); } @Override publicvoidonListItemClick(ListViewl,Viewv,intposition,longid){ //Dosomethingwhenalistitemisclicked } }
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