AsyncQueryHandler

最新推荐文章于 2025-08-11 21:24:53 发布

iteye_13411

最新推荐文章于 2025-08-11 21:24:53 发布

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文章标签：移动开发数据库

本文深入解析了Android中AsyncQueryHandler类的功能与用法，通过两个具体实例展示了如何使用该类进行异步数据查询，并更新UI。同时介绍了如何通过监听QueryComplete事件来实现数据更新后的同步显示。

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android.content.AsyncQueryHandler继续于android.os.Handler

虽然Handler自己是没另开新线程,但是AsyncQueryHandler自己却是另开了一个线程来进行数据的查询
实例1 AsyncQueryHandler-->同步更新 classQueryHandlerextendsAsyncQueryHandler{ QueryHandler(ContentResolverres){ super(res);//[这里让AsyncQueryHandler和ContentResolver联系起来] } @Override protectedvoidonQueryComplete(inttoken,Objectcookie,Cursorcursor)//监听QueryComplete事件 { mActivity.init(cursor); } } AsyncQueryHandler--->当contentProvied发生变化时候同步更新显示就可以通过使用AsyncQueryHandler类来达到这一要求 上面的代码--->onQueryComplete()--->就是当cursor更新完之后的 publicvoidinit(Cursorc){ mAdapter.changeCursor(c); if(mQueryCursor==null){ MusicUtils.displayDatabaseError(this); setListAdapter(null); mReScanHandler.sendEmptyMessageDelayed(0,1000); } MusicUtils.hideDatabaseError(this); } 实例2： packagecom.android.phone; importstaticandroid.view.Window.PROGRESS_VISIBILITY_OFF; importstaticandroid.view.Window.PROGRESS_VISIBILITY_ON; importandroid.app.ListActivity; importandroid.content.AsyncQueryHandler; importandroid.content.ContentResolver; importandroid.content.Intent; importandroid.database.Cursor; importandroid.net.Uri; importandroid.os.Bundle; importandroid.util.Log; importandroid.view.Window; importandroid.widget.CursorAdapter; importandroid.widget.SimpleCursorAdapter; importandroid.widget.TextView; /** *ADNListactivityforthePhoneapp. */ publicclassADNListextendsListActivity{ protectedstaticfinalStringTAG="ADNList"; protectedstaticfinalbooleanDBG=false; privatestaticfinalString[]COLUMN_NAMES=newString[]{ "name", "number" }; protectedstaticfinalintNAME_COLUMN=0; protectedstaticfinalintNUMBER_COLUMN=1; privatestaticfinalint[]VIEW_NAMES=newint[]{ android.R.id.text1, android.R.id.text2 }; protectedstaticfinalintQUERY_TOKEN=0; protectedstaticfinalintINSERT_TOKEN=1; protectedstaticfinalintUPDATE_TOKEN=2; protectedstaticfinalintDELETE_TOKEN=3; protectedQueryHandlermQueryHandler; protectedCursorAdaptermCursorAdapter; protectedCursormCursor=null; privateTextViewmEmptyText; protectedintmInitialSelection=-1; @Override protectedvoidonCreate(Bundleicicle){ super.onCreate(icicle); getWindow().requestFeature(Window.FEATURE_INDETERMINATE_PROGRESS); setContentView(R.layout.adn_list); mEmptyText=(TextView)findViewById(android.R.id.empty); mQueryHandler=newQueryHandler(getContentResolver()); } @Override protectedvoidonResume(){ super.onResume(); query(); } @Override protectedvoidonStop(){ super.onStop(); if(mCursor!=null){ mCursor.deactivate(); } } protectedUriresolveIntent(){ Intentintent=getIntent(); if(intent.getData()==null){ intent.setData(Uri.parse("content://icc/adn")); } returnintent.getData(); } privatevoidquery(){ Uriuri=resolveIntent(); if(DBG)log("query:startinganasyncquery"); mQueryHandler.startQuery(QUERY_TOKEN,null,uri,COLUMN_NAMES, null,null,null); displayProgress(true); } privatevoidreQuery(){ query(); } privatevoidsetAdapter(){ if(mCursorAdapter==null){ mCursorAdapter=newAdapter(); setListAdapter(mCursorAdapter); }else{ mCursorAdapter.changeCursor(mCursor); } if(mInitialSelection>=0&&mInitialSelection<mCursorAdapter.getCount()){ setSelection(mInitialSelection); getListView().setFocusableInTouchMode(true); booleangotfocus=getListView().requestFocus(); } } protectedCursorAdapternewAdapter(){ returnnewSimpleCursorAdapter(this, android.R.layout.simple_list_item_2, mCursor,COLUMN_NAMES,VIEW_NAMES); } privatevoiddisplayProgress(booleanflag){ if(DBG)log("displayProgress:"+flag); mEmptyText.setText(flag?R.string.simContacts_emptyLoading:R.string.simContacts_empty); getWindow().setFeatureInt( Window.FEATURE_INDETERMINATE_PROGRESS, flag?PROGRESS_VISIBILITY_ON:PROGRESS_VISIBILITY_OFF); } privateclassQueryHandlerextendsAsyncQueryHandler{ publicQueryHandler(ContentResolvercr){ super(cr); } @Override protectedvoidonQueryComplete(inttoken,Objectcookie,Cursorc){//监听QueryComplete事件 if(DBG)log("onQueryComplete:cursor.count="+c.getCount()); mCursor=c; setAdapter(); displayProgress(false); ? @Override protectedvoidonInsertComplete(inttoken,Objectcookie,//监听InsertComplete事件 Uriuri){ if(DBG)log("onInsertComplete:requery"); reQuery(); } @Override protectedvoidonUpdateComplete(inttoken,Objectcookie,intresult){//监听onUpdateComplete事件 if(DBG)log("onUpdateComplete:requery"); reQuery(); } @Override protectedvoidonDeleteComplete(inttoken,Objectcookie,intresult){//监听DeleteComplete事件 if(DBG)log("onDeleteComplete:requery"); reQuery(); } } protectedvoidlog(Stringmsg){ Log.d(TAG,"[ADNList]"+msg); } }