Activity启动?(慎入)

ActivityThread#main

在ActivityThread中值得关注的成员变量

//Binder本地对象，ams 与 应用程序进行通信的中介
final ApplicationThread mAppThread = new ApplicationThread();
    
final H mH = new H();
private class H extends Handler......

ActivityThread#attach

ActivityManagerProxy#attachApplication

将ApplicationThread 对象写入到Parcel对象的data中，然后ActivityManagerProxy的内部Binder对象mRemote向ActivityManagerService发送一个ATTACH_APPLICATION_TRANSACTION进程间通信请求

上面的动作都是在Application 进程中执行的，下面的就会在ams中执行了

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Android系统源代码情景分析

然后ams向我们的应用进程发送一个LAUNCH_ACTIVITY_TRANSACTION进程通信请求

然后我们的应用进程的ApplicationThread的scheduleLaunchActivity方法处理这个请求

ApplicationThread#scheduleLaunchActivity

最终通过mH(Handler实例)发送Message

ActivityThread#mH#handleMessage

ActivityThread#handleLaunchActivity

unscheduleGcIdler

从主线程的MessageQueue中的IdleHandler list中移除用于gc的IdleHandler
WindowManagerGlobal.initialize();

初始化wms，得到wms实例

ActivityThread#performLaunchActivity

ActivityInfo

    /**
     * Information you can retrieve about a particular application
     * activity or receiver. This corresponds to information collected
     * from the AndroidManifest.xml's  and
     *  tags.
     */

包含一个特殊activity/receiver 的一些信息，跟你在AndroidManifest文件写的是一样的
就是描述启动Activity的一些信息咯

ComponentName

    /**
     * Identifier for a specific application component
     * ({@link android.app.Activity}, {@link android.app.Service},
     * {@link android.content.BroadcastReceiver}, or
     * {@link android.content.ContentProvider}) that is available.  Two
     * pieces of information, encapsulated here, are required to identify
     * a component: the package (a String) it exists in, and the class (a String)
     * name inside of that package.
     * 
     */

描述着Activity/BroadcastReceiver/ContentProvider/Service 其中一个的信息，分别是

    private final String mPackage;//描述包的路径   
    private final String mClass;//类名

Instrumentation

介绍Instrumentation

     public Activity newActivity(ClassLoader cl, String className,
        Intent intent)
        throws InstantiationException, IllegalAccessException,
        ClassNotFoundException {
            return (Activity)cl.loadClass(className).newInstance();
    }

通过反射创建了一个Activity

Application app = r.packageInfo.makeApplication(false, mInstrumentation);
packageInfo 是一个LoadedApk的实例
然后再这个方法里面
```
  ContextImpl appContext = ContextImpl.createAppContext(mActivityThread, this);
     app = mActivityThread.mInstrumentation.newApplication(
             cl, appClass, appContext);
```
创建了一个全局的Context对象，还有一个Application对象
在newApplication方法中调用了Application的attach方法，将Context对象赋值给ContextWrapper的成员变量mBase

     static public Application newApplication(Class clazz, Context context)
        throws InstantiationException, IllegalAccessException, 
        ClassNotFoundException {
        Application app = (Application)clazz.newInstance();
        ........        
        return app;
    }

activity.attach
我们直接分析attach方法
mInstrumentation.callActivityOnCreate

    prePerformCreate(activity);
    activity.performCreate(icicle);
    postPerformCreate(activity);
    //------
    final void performCreate(Bundle icicle) {
        restoreHasCurrentPermissionRequest(icicle);
        onCreate(icicle);//常见?
        mActivityTransitionState.readState(icicle);
        performCreateCommon();
    }

然后再回到ActivityThread#handleLaunchActivity中

来到最后一个handleResumeActivity方法

handleResumeActivity

在handleResumeActivity中调用Activity的performResume方法，然后在performResumeActivity方法调用Activity的performRestart，在performRestart调用Activity的performStart，然后再performStart调用Activity的onStart方法。
然后回到Activity的performResume方法中，再通过Instrumentation调用Activity的onResume方法
然后回到 handleResumeActivity，在Activity调用onResume之后

void makeVisible() {
    if (!mWindowAdded) {
        ViewManager wm = getWindowManager();
        wm.addView(mDecor, getWindow().getAttributes());
        mWindowAdded = true;
    }
    mDecor.setVisibility(View.VISIBLE);
}

然后我们才能看到我们的界面

最后

带有目的性去看才有意义