Handler Looper与MessageQueue源码分析.docx

HandlerLooper与MessageQueue源码分析在Android中可以通过Handler来更新主线程中UI的变化，更新UI只能在主线程中进行更新，而为了让其他线程也能控制UI的变化，Android提供了一种机制Handler、Looper与MessageQueue一同协作来达到其他线程更新UI的目的。作者：idisfkj来源：segmentfault|2016-10-21 13:03?收藏??分享在Android中可以通过Handler来更新主线程中UI的变化，更新UI只能在主线程中进行更新，而为了让其他线程也能控制UI的变化，Android提供了一种机制Handler、Looper与MessageQueue一同协作来达到其他线程更新UI的目的。一般我们会在主线程中通过如下方法定义一个Handlerprivate?Handler?mHandler?=?new?Handler()?{?????????@Override?????????public?void?handleMessage(Message?msg)?{?????????????tv.setText(mHandler?change?UI);?????????????super.handleMessage(msg);?????????}?????};??一般都见不到Looper与MessageQueue的，那么它们都是在哪里调用与如何协作的呢?在主线程不会显式的调用Looper而是会在ActivityThread.main方法中默认调用。public?static?void?main(String[]?args)?{??????????Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER,?ActivityThreadMain);?????????SamplingProfilerIntegration.start();???????????//?CloseGuard?defaults?to?true?and?can?be?quite?spammy.??We?????????//?disable?it?here,?but?selectively?enable?it?later?(via?????????//?StrictMode)?on?debug?builds,?but?using?DropBox,?not?logs.?????????CloseGuard.setEnabled(false);???????????Environment.initForCurrentUser();???????????//?Set?the?reporter?for?event?logging?in?libcore?????????EventLogger.setReporter(new?EventLoggingReporter());???????????//?Make?sure?TrustedCertificateStore?looks?in?the?right?place?for?CA?certificates?????????final?File?configDir?=?Environment.getUserConfigDirectory(UserHandle.myUserId());??????????TrustedCertificateStore.setDefaultUserDirectory(configDir);???????????Process.setArgV0(pre-initialized);???????????Looper.prepareMainLooper();//创建Looper???????????ActivityThread?thread?=?new?ActivityThread();?????????thread.attach(false);???????????if?(sMainThreadHandler?==?null)?{?????????????sMainThreadHandler?=?thread.getHandler();?????????}???????????if?(false)?{?????????????Looper.myLooper().setMessageLogging(new?????????????????????LogPrinter(Log.DEBUG,?ActivityThread));?????????}???????????//?End?of?event?ActivityThreadMain.??????????Trace.traceEnd(Trace.TRAC