Android数据库内容变化的监听（附件1）

最新推荐文章于 2021-10-09 12:25:35 发布

最新推荐文章于 2021-10-09 12:25:35 发布 · 74 阅读

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本文深入探讨了AbstractCursor类在数据处理中的核心作用，通过简洁的API提供了一种方便、高效的跨进程数据交互方式。重点介绍了如何利用此类进行数据查询、更新和观察，确保数据的实时同步与通知机制。从抽象概念到具体应用，为开发者提供了实用的指南。

AbstractCursor.java文件
/**
*Thisisanabstractcursorclassthathandlesalotofthecommoncode
*thatallcursorsneedtodealwithandisprovidedforconveniencereasons.
*/
publicabstractclassAbstractCursorimplementsCrossProcessCursor{
privatestaticfinalStringTAG="Cursor";

DataSetObservablemDataSetObservable=newDataSetObservable();
ContentObservablemContentObservable=newContentObservable();

-------------------省略------------------

publicvoiddeactivate(){
deactivateInternal();
}

/**
*@hide
*/
publicvoiddeactivateInternal(){
if(mSelfObserver!=null){
mContentResolver.unregisterContentObserver(mSelfObserver);
mSelfObserverRegistered=false;
}
mDataSetObservable.notifyInvalidated();
}

publicbooleanrequery(){
if(mSelfObserver!=null&&mSelfObserverRegistered==false){
mContentResolver.registerContentObserver(mNotifyUri,true,mSelfObserver);
mSelfObserverRegistered=true;
}
mDataSetObservable.notifyChanged();
returntrue;
}

publicbooleanisClosed(){
returnmClosed;
}

publicvoidclose(){
mClosed=true;
mContentObservable.unregisterAll();
deactivateInternal();
}

-------------------省略------------------
publicvoidregisterContentObserver(ContentObserverobserver){
mContentObservable.registerObserver(observer);
}

publicvoidunregisterContentObserver(ContentObserverobserver){
//cursorwillunregisterallobserverswhenitclose
if(!mClosed){
mContentObservable.unregisterObserver(observer);
}
}

/**
*Thisishiddenuntilthedatasetchangemodelhasbeenre-evaluated.
*@hide
*/
protectedvoidnotifyDataSetChange(){
mDataSetObservable.notifyChanged();
}

/**
*Thisishiddenuntilthedatasetchangemodelhasbeenre-evaluated.
*@hide
*/
protectedDataSetObservablegetDataSetObservable(){
returnmDataSetObservable;

}
publicvoidregisterDataSetObserver(DataSetObserverobserver){
mDataSetObservable.registerObserver(observer);

}

publicvoidunregisterDataSetObserver(DataSetObserverobserver){
mDataSetObservable.unregisterObserver(observer);
}

/**
*Subclassesmustcallthismethodwhentheyfinishcommittingupdatestonotifyall
*observers.
*
*@paramselfChange
*/
protectedvoidonChange(booleanselfChange){
synchronized(mSelfObserverLock){
mContentObservable.dispatchChange(selfChange);
if(mNotifyUri!=null&&selfChange){
mContentResolver.notifyChange(mNotifyUri,mSelfObserver);
}
}
}

/**
*SpecifiesacontentURItowatchforchanges.
*
*@paramcrThecontentresolverfromthecaller'scontext.
*@paramnotifyUriTheURItowatchforchanges.Thiscanbea
*specificrowURI,orabaseURIforawholeclassofcontent.
*/
publicvoidsetNotificationUri(ContentResolvercr,UrinotifyUri){
synchronized(mSelfObserverLock){
mNotifyUri=notifyUri;
mContentResolver=cr;
if(mSelfObserver!=null){
mContentResolver.unregisterContentObserver(mSelfObserver);
}
mSelfObserver=newSelfContentObserver(this);
mContentResolver.registerContentObserver(mNotifyUri,true,mSelfObserver);
mSelfObserverRegistered=true;
}
}
-------------------省略------------------
@Override
protectedvoidfinalize(){
if(mSelfObserver!=null&&mSelfObserverRegistered==true){
mContentResolver.unregisterContentObserver(mSelfObserver);
}
}

/**
*CursorsusethisclasstotrackchangesothersmaketotheirURI.
*/
protectedstaticclassSelfContentObserverextendsContentObserver{
WeakReference<AbstractCursor>mCursor;

publicSelfContentObserver(AbstractCursorcursor){
super(null);
mCursor=newWeakReference<AbstractCursor>(cursor);
}

@Override
publicbooleandeliverSelfNotifications(){
returnfalse;
}

@Override
publicvoidonChange(booleanselfChange){
AbstractCursorcursor=mCursor.get();
if(cursor!=null){
cursor.onChange(false);
}
}
}
-------------------省略------------------
protectedContentResolvermContentResolver;
protectedbooleanmClosed=false;
privateUrimNotifyUri;
privateContentObservermSelfObserver;
finalprivateObjectmSelfObserverLock=newObject();
privatebooleanmSelfObserverRegistered;
}