Application 启动流程

本文共分为三个部分

1.Application的父类关系

2.Application在什么时候创建到

3.Application的Context是在什么时候创建到，

1.Application的关系图还是比较简单的，画个图大家来了解一下即可。

2.Application是在什么时候创建的，

最近看到一篇文章说application是在Bind Applicationd的时候创建的，这只是四种创建方式之一。

下面我们来详细的了解一下其他的启动方式：

1.activity启动的时候，会创建Application

2.broadcast接受的时候，会创建Application

3.Service启动的时候，会创建Application

4.bindApplication的时候，会创建application（这个可能大家会疑惑时什么时候，稍后详细介绍）

首先来介绍前公共流程：

对于前三个，很容易理解，但第四个是什么时候呢，下面我们来专门对第四个来分析一下，

step1：SystemServer.java

@Override    public void run() {

 .......

            Slog.i(TAG, "Activity Manager");            context = ActivityManagerService.main(factoryTest);
 .......

}

step2  :   ActivityManagerService.java

    public static final Context main(int factoryTest) {        AThread thr = new AThread();        thr.start();

ActivityThread at = ActivityThread.systemMain();
｝

step 3 ： ActivityThread.java

public static ActivityThread systemMain() {5022        HardwareRenderer.disable(true);5023        ActivityThread thread = new ActivityThread();5024        thread.attach(true);5025        return thread;5026    }

step 4 ： ActivityManagerService.java

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

private final boolean attachApplicationLocked(IApplicationThread thread, int pid) {

      ......
            thread.bindApplication(processName, appInfo, providers,                    app.instrumentationClass, profileFile, profileFd, profileAutoStop,                    app.instrumentationArguments, app.instrumentationWatcher,                   app.instrumentationUiAutomationConnection, testMode, enableOpenGlTrace,                   isRestrictedBackupMode || !normalMode, app.persistent,                   new Configuration(mConfiguration), app.compat, getCommonServicesLocked(),                   mCoreSettingsObserver.getCoreSettingsLocked());
......
｝

step5 : ActivityThread.java

        public final void bindApplication(String processName,                ApplicationInfo appInfo, List<ProviderInfo> providers,                ComponentName instrumentationName, String profileFile,                ParcelFileDescriptor profileFd, boolean autoStopProfiler,                Bundle instrumentationArgs, IInstrumentationWatcher instrumentationWatcher,                IUiAutomationConnection instrumentationUiConnection, int debugMode,                boolean enableOpenGlTrace, boolean isRestrictedBackupMode, boolean persistent,                Configuration config, CompatibilityInfo compatInfo, Map<String, IBinder> services,                Bundle coreSettings) {

......

            queueOrSendMessage(H.BIND_APPLICATION, data);

}

case BIND_APPLICATION:1314                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "bindApplication");1315                    AppBindData data = (AppBindData)msg.obj;1316                    handleBindApplication(data);

到这里我们可以清理的了解到，这套流程是最系统启动的时候就完成的。

第三部分：Application的Context是什么时候创建的

    public Application makeApplication(boolean forceDefaultAppClass,            Instrumentation instrumentation) {        if (mApplication != null) {           return mApplication;        }       Application app = null;        String appClass = mApplicationInfo.className;        if (forceDefaultAppClass || (appClass == null)) {            appClass = "android.app.Application";        }        try {            java.lang.ClassLoader cl = getClassLoader();            ContextImpl appContext = new ContextImpl();            appContext.init(this, null, mActivityThread);            app = mActivityThread.mInstrumentation.newApplication(                    cl, appClass, appContext);            appContext.setOuterContext(app);        } catch (Exception e) {            if (!mActivityThread.mInstrumentation.onException(app, e)) {               throw new RuntimeException(                    "Unable to instantiate application " + appClass                    + ": " + e.toString(), e);            }        }        mActivityThread.mAllApplications.add(app);        mApplication = app;

......

}

这里的mApplication就是我们所要获取的Context，

当我们调用getApplicationContext返回的就是这个对象。

谢谢！

215            Slog.i(TAG, "Activity Manager");216            context = ActivityManagerService.main(factoryTest);

1462    public static final Context main(int factoryTest) {1463        AThread thr = new AThread();1464        thr.start();1465

487    public Application makeApplication(boolean forceDefaultAppClass,488            Instrumentation instrumentation) {489        if (mApplication != null) {490            return mApplication;491        }492493        Application app = null;494495        String appClass = mApplicationInfo.className;496        if (forceDefaultAppClass || (appClass == null)) {497            appClass = "android.app.Application";498        }499500        try {501            java.lang.ClassLoader cl = getClassLoader();502            ContextImpl appContext = new ContextImpl();503            appContext.init(this, null, mActivityThread);504            app = mActivityThread.mInstrumentation.newApplication(505                    cl, appClass, appContext);506            appContext.setOuterContext(app);507        } catch (Exception e) {508            if (!mActivityThread.mInstrumentation.onException(app, e)) {509                throw new RuntimeException(510                    "Unable to instantiate application " + appClass511                    + ": " + e.toString(), e);512            }513        }514        mActivityThread.mAllApplications.add(app);515        mApplication = app;