App启动流程

一、先简单介绍下点击手机桌面(也就是Launcher界面)点击某个App的启动过程

App启动过程.png App启动过程.png 应用启动整体概念.png 应用程序启动涉及的进程间通信.png

从上面的几个图我们也可以清晰的看到

1、首先点击Launcher中的某个App，会调用startActivity，它通过binder进程间通信与AMS进行通信，AMS通过socket与Zygote进程通信，请求fork孵化出APP进程即会调用ActivityThread.main()方法。 这就是基本流程

二、分析源码ActivityThread如何实例化Application和MainActivity的

2.1 ActivityThread.java中的main()方法

这里需要注意的是创建了MainLooper， 并使其loop()轮询事件，而且还实例化了ActivityThread,并调用器attach方法

        Looper.prepareMainLooper();

        ...
        ActivityThread thread = new ActivityThread();
        thread.attach(false, startSeq);

        ...
        Looper.loop();

attach()方法

 private void attach(boolean system, long startSeq) {
final IActivityManager mgr = ActivityManager.getService();
            try {
7080行                mgr.attachApplication(mAppThread, startSeq);
            } catch (RemoteException ex) {
                throw ex.rethrowFromSystemServer();
            }
  ...
}

2.2 在attch方法中又调用了ActivityManagerService.attachApplication方法，在attachApplication方法中又调用了attachApplicationLocked()方法

在该方法中又通过thread(即ApplicationThread)(ApplicationThread又是ActivityThread的子类)又回调了bindApplication()方法

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

5049行 thread.bindApplication(processName, appInfo, providers,
                    ...);

...
5101行
// See if the top visible activity is waiting to run in this process...
        if (normalMode) {
            try {
                didSomething = mAtmInternal.attachApplication(app.getWindowProcessController());
            } catch (Exception e) {
                Slog.wtf(TAG, "Exception thrown launching activities in " + app, e);
                badApp = true;
            }
        }

2.3 在ActivityThread中的bindApplication()中将传回的数据封装为AppBindData实列，并发送了一个H.BIND_APPLICATION Handler消息。

在Hanlder接受消息的地方又调用了handleBindApplication(data)方法。

6122行 private void handleBindApplication(AppBindData data) {
...

6431行 app = data.info.makeApplication(data.restrictedBackupMode, null);
                6460行 mInstrumentation.callApplicationOnCreate(app);
...
}

6431行通过LoaderApk.makeApplication反射创建Application实例

            app = mActivityThread.mInstrumentation.newApplication(
                    cl, appClass, appContext);

6460行通过Instrumentation.callApplicationOnCreate调用onCreate()方法

2.4 到这里Application已经创建完成了，接着需要创建第一个Activity，y也就是主Activity

回到2.2, 在ActivityManagerService.attachApplicationLocked()中的5101行，又调用了mAtmInternal.attachApplication

而mAtmInternal是ActivityTaskManagerInternal，它是个抽象类，真正实现在ActivityTaskManagerService中，而ActivityTaskManagerService.attachApplication方法又调用了

RootActivityContainer.attachApplication方法

ActivityTaskManagerService.java

        public boolean attachApplication(WindowProcessController wpc) throws RemoteException {
            synchronized (mGlobalLockWithoutBoost) {
                return mRootActivityContainer.attachApplication(wpc);
            }
        }

2.5 在RootActivityContainer.attachApplication方法中，会从AndroidMainfest.xml解析的Activity信息栈中获取到第一个activity，即为主Activity。

boolean attachApplication(WindowProcessController app) throws RemoteException {
...
            final ActivityRecord top = stack.topRunningActivityLocked();
              
                for (int i = 0; i < size; i++) {
                    final ActivityRecord activity = mTmpActivityList.get(i);
                    if (activity.app == null && app.mUid == activity.info.applicationInfo.uid
                            && processName.equals(activity.processName)) {
                        try {
783行                            if (mStackSupervisor.realStartActivityLocked(activity, app,
                                    top == activity /* andResume */, true /* checkConfig */)) {
                                didSomething = true;
                            }
                        } catch (RemoteException e) {
                            Slog.w(TAG, "Exception in new application when starting activity "
                                    + top.intent.getComponent().flattenToShortString(), e);
                            throw e;
                        }
                    }
                }
...
}

783行，判断如果Activity是主Actiivty就开始进行实例，其实后面的流程和《App startActivity启动流程(AMS)》一致，这里就略过了。