Android数据库内容变化的监听（附件2）

最新推荐文章于 2025-11-26 14:12:29 发布

最新推荐文章于 2025-11-26 14:12:29 发布 · 81 阅读

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本文详细介绍了CursorAdapter类的实现原理、初始化方法、如何改变底层游标、自动查询逻辑以及观察者模式的应用，旨在帮助开发者理解并有效利用CursorAdapter进行数据适配。

publicabstractclassCursorAdapterextendsBaseAdapterimplementsFilterable,
CursorFilter.CursorFilterClient{
-------------------省略------------------
protectedChangeObservermChangeObserver;
/**
*Thisfieldshouldbemadeprivate,soitishiddenfromtheSDK.
*{@hide}
*/
protectedDataSetObservermDataSetObserver=newMyDataSetObserver();
/**
*Thisfieldshouldbemadeprivate,soitishiddenfromtheSDK.
*{@hide}
*/
-------------------省略------------------
publicCursorAdapter(Contextcontext,Cursorc){
init(context,c,true);
}
-------------------省略------------------
protectedvoidinit(Contextcontext,Cursorc,booleanautoRequery){
booleancursorPresent=c!=null;
mAutoRequery=autoRequery;
mCursor=c;
mDataValid=cursorPresent;
mContext=context;
mRowIDColumn=cursorPresent?c.getColumnIndexOrThrow("_id"):-1;
mChangeObserver=newChangeObserver();
if(cursorPresent){
c.registerContentObserver(mChangeObserver);
c.registerDataSetObserver(mDataSetObserver);
}
}
-------------------省略------------------
/**
*Changetheunderlyingcursortoanewcursor.Ifthereisanexistingcursoritwillbe
*closed.
*
*@paramcursorthenewcursortobeused
*/
publicvoidchangeCursor(Cursorcursor){
if(cursor==mCursor){
return;
}
if(mCursor!=null){
mCursor.unregisterContentObserver(mChangeObserver);
mCursor.unregisterDataSetObserver(mDataSetObserver);
mCursor.close();
}
mCursor=cursor;
if(cursor!=null){
cursor.registerContentObserver(mChangeObserver);
cursor.registerDataSetObserver(mDataSetObserver);
mRowIDColumn=cursor.getColumnIndexOrThrow("_id");
mDataValid=true;
//notifytheobserversaboutthenewcursor
notifyDataSetChanged();
}else{
mRowIDColumn=-1;
mDataValid=false;
//notifytheobserversaboutthelackofadataset
notifyDataSetInvalidated();
}
}
-------------------省略------------------
/**
*Calledwhenthe{@linkContentObserver}onthecursorreceivesachangenotification.
*Thedefaultimplementationprovidestheauto-requerylogic,butmaybeoverriddenby
*subclasses.
*
*@seeContentObserver#onChange(boolean)
*/
protectedvoidonContentChanged(){
if(mAutoRequery&&mCursor!=null&&!mCursor.isClosed()){
if(Config.LOGV)Log.v("Cursor","Autorequerying"+mCursor+"duetoupdate");
mDataValid=mCursor.requery();
}
}

privateclassChangeObserverextendsContentObserver{
publicChangeObserver(){
super(newHandler());
}

@Override
publicbooleandeliverSelfNotifications(){
returntrue;
}

@Override
publicvoidonChange(booleanselfChange){
onContentChanged();
}
}

privateclassMyDataSetObserverextendsDataSetObserver{
@Override
publicvoidonChanged(){
mDataValid=true;
notifyDataSetChanged();
}
@Override
publicvoidonInvalidated(){
mDataValid=false;
notifyDataSetInvalidated();
}
}
}