Android 四大组件之ContentProvider工作原理

本文主要是介绍Android 四大组件之ContentProvider工作原理，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

ContentProvider启动

ContentProvider是一种内容共享型组件，实际上它是通过Binder向其它应用提供数据。当ContentProvider所在的进程启动时，ContentProvider会同时启动并被发布到AMS中，需要特别注意的是ContentProvider的onCreate方法要早于Application的onCreate方法执行。

废话不多说先看源码,As we all known,每个进程的入口都是ActivityThread.main

public static void main(String[] args) {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 libcoreEventLogger.setReporter(new EventLoggingReporter());Security.addProvider(new AndroidKeyStoreProvider());// Make sure TrustedCertificateStore looks in the right place for CA certificatesfinal File configDir = Environment.getUserConfigDirectory(UserHandle.myUserId());TrustedCertificateStore.setDefaultUserDirectory(configDir);Process.setArgV0("<pre-initialized>");Looper.prepareMainLooper();ActivityThread thread = new ActivityThread();thread.attach(false);if (sMainThreadHandler == null) {sMainThreadHandler = thread.getHandler();}AsyncTask.init();if (false) {Looper.myLooper().setMessageLogging(newLogPrinter(Log.DEBUG, "ActivityThread"));}Looper.loop();throw new RuntimeException("Main thread loop unexpectedly exited");}

主要看attach方法

private void attach(boolean system) {...final IActivityManager mgr = ActivityManagerNative.getDefault();try {mgr.attachApplication(mAppThread);} catch (RemoteException ex) {// Ignore}
...
}

通过前面的分析，这里一眼就可以看出IPC通信调用AMS的同名方法，接着往下看ActivityManagerService.java

    @Overridepublic final void attachApplication(IApplicationThread thread) {synchronized (this) {int callingPid = Binder.getCallingPid();final long origId = Binder.clearCallingIdentity();attachApplicationLocked(thread, callingPid);Binder.restoreCallingIdentity(origId);}}

AMS.attachApplicationLocked这个方法也是很长，这里截取最关键的

private final boolean attachApplicationLocked(IApplicationThread thread,int pid) {...ProfilerInfo profilerInfo = profileFile == null ? null: new ProfilerInfo(profileFile, profileFd, samplingInterval, profileAutoStop);thread.bindApplication(processName, appInfo, providers, app.instrumentationClass,profilerInfo, app.instrumentationArguments, app.instrumentationWatcher,app.instrumentationUiAutomationConnection, testMode, enableOpenGlTrace,isRestrictedBackupMode || !normalMode, app.persistent,new Configuration(mConfiguration), app.compat, getCommonServicesLocked(),mCoreSettingsObserver.getCoreSettingsLocked());updateLruProcessLocked(app, false, null);...
}

这里又IPC通信，返回客户端处理去了
总结一下，跟ContentProvider相关的事件

1.创建ActivityThread实例，并创建消息队列

2.ActivityThread的attach方法远程调用AMS的attachApplication方法，并将ApplicationThread对象传递给AMS。

3.AMS的attachApplication方法中会调用ApplicationThread的bingApplication（IPC调用）进而通过H对象切换到ActivityThread中执行handleBindApplication方法

这个方法有200多行，这里截取了最后比较关键的部分