Android 探索Activity中mDecor变量何时赋值

参考书籍:<Android 系统源代码情景分析 第3版>
看书时,好些书都会提到Activity中的makeVisible(),这个方法会用到mDecor变量,但是很少有说这个变量何时赋值的.

• AMS发出启动Activity

// ActivityStack.java
public class ActivityStack {
    final boolean realStartActivityLocked(ActivityRecord r,ProcessRecord app, boolean andResume, boolean checkConfig)throws RemoteException {
        ...
        try {
            ...
            // app.thread 是ActivityThread.ApplicationThread 它是一个Binder本地对象.
            // 这里就从AMS切换到应用APP进程中了.
            app.thread.scheduleLaunchActivity(new Intent(r.intent), r,
                    System.identityHashCode(r),
                    r.info, r.icicle, results, newIntents, !andResume,
                    mService.isNextTransitionForward());
            ...
        } catch (RemoteException e) {
            ...
        }
        ...
        return true;
    }
}
// 启动Activity
// ActivityThread.ApplicationThread.java
public final class ActivityThread {
    private final class ApplicationThread extends ApplicationThreadNative {
        public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident,t,ActivityInfo info, Bundle state, List<ResultInfo> pendingResults,List<Intent> pendingNewIntents, boolean notResumed, boolean isForward) {
            // 创建一个目标ActivityClientRecord对象
            ActivityClientRecord r = new ActivityClientRecord();
            r.token = token;
            r.ident = ident;
            r.intent = intent;
            r.activityInfo = info;
            r.state = state;
            r.pendingResults = pendingResults;
            r.pendingIntents = pendingNewIntents;
            r.startsNotResumed = notResumed;
            r.isForward = isForward;
            // TODO 第一
            queueOrSendMessage(H.LAUNCH_ACTIVITY, r);
        }
    }
    // TODO 第一
    private final void queueOrSendMessage(int what, Object obj, int arg1, int arg2) {
        synchronized (this) {
            Message msg = Message.obtain();
            msg.what = what;
            msg.obj = obj;
            msg.arg1 = arg1;
            msg.arg2 = arg2;
            // TODO 第二
            mH.sendMessage(msg);
        }
    }
    private final class H extends Handler {
        // TODO 第二
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case LAUNCH_ACTIVITY: {
                    // 取出刚刚在ApplicationThread.scheduleLaunchActivity中创建的ActivityClientRecord对象
                    ActivityClientRecord r = (ActivityClientRecord)msg.obj;
                    r.packageInfo = getPackageInfoNoCheck(r.activityInfo.applicationInfo);
                    // TODO 第三
                    handleLaunchActivity(r, null);
                } 
                break;
            }
        }
    }
    // TODO 第三
    private final void handleLaunchActivity(ActivityClientRecord r, Intent customIntent) {
        // TODO 第四
        Activity a = performLaunchActivity(r, customIntent);
        if (a != null) {
            r.createdConfig = new Configuration(mConfiguration);
            Bundle oldState = r.state;
            // TODO 第五 
            // 第四步中,创建好了目标Activity,WindowPhone,mDecorView.
            handleResumeActivity(r.token, false, r.isForward);
            ...
        } else {
            ...
        }
    }
    // TODO 第四 
    private final Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
        ...
        Activity activity = null;
        try {
            // 通过类加载器创建 Activity对象
            java.lang.ClassLoader cl = r.packageInfo.getClassLoader();
            activity = mInstrumentation.newActivity(
                    cl, component.getClassName(), r.intent);
            r.intent.setExtrasClassLoader(cl);
            if (r.state != null) {
                r.state.setClassLoader(cl);
            }
        } catch (Exception e) {
            ...
        }
        try {
            // 创建 Application 对象
            Application app = r.packageInfo.makeApplication(false, mInstrumentation);
            ...
            if (activity != null) {
                ContextImpl appContext = new ContextImpl();
                appContext.init(r.packageInfo, r.token, this);
                appContext.setOuterContext(activity);
                CharSequence title = r.activityInfo.loadLabel(appContext.getPackageManager());
                Configuration config = new Configuration(mConfiguration);
                ...
                // 执行Activity中attach()方法,attach()中会创建Activity的PhoneWindow和WindowManagerImpl等对象
                activity.attach(appContext, this, getInstrumentation(), r.token,
                        r.ident, app, r.intent, r.activityInfo, title, r.parent,
                        r.embeddedID, r.lastNonConfigurationInstance,
                        r.lastNonConfigurationChildInstances, config);
    
                if (customIntent != null) {
                    activity.mIntent = customIntent;
                }
                r.lastNonConfigurationInstance = null;
                r.lastNonConfigurationChildInstances = null;
                activity.mStartedActivity = false;
                int theme = r.activityInfo.getThemeResource();
                if (theme != 0) {
                    activity.setTheme(theme);
                }
    
                activity.mCalled = false;  
                // 这里最终会调用到经常用到的Activity中的onCreate().
                // onCreate()最终会创建一个mDecorView对象, 我们一般使用的布局文件就是被加入到mDecorView的子布局系统文件的id为content的ViewGroup中.
                mInstrumentation.callActivityOnCreate(activity, r.state);
                ...
                r.activity = activity;
                r.stopped = true;
                ...
            }
            r.paused = true;
            // mActivities对象的类型 HashMap<IBinder, ActivityClientRecord>.
            // 它作用是ActivityClientRecord与token值一一对应记录起来.
            mActivities.put(r.token, r);
        } catch (SuperNotCalledException e) {
            throw e;
        } catch (Exception e) {
            ...
        }
        return activity;
    }
    // TODO 第五
    final void handleResumeActivity(IBinder token, boolean clearHide, boolean isForward) {
        ...
        // performResumeActivity最终执行下去会调用Activity中我们非常熟悉的,调用链如下:
        // performResumeActivity
        // Activity.performResume()
        // Instrumentation.callActivityOnResume()
        // Activity.onResume()
        ActivityClientRecord r = performResumeActivity(token, clearHide);
        if (r != null) {
            final Activity a = r.activity;
            ...
            if (r.window == null && !a.mFinished && willBeVisible) {
                // 从目标Actity中获取PhoneWindow对象
                r.window = r.activity.getWindow();
                // 获取PhoneWindow中的mDecorView对象
                View decor = r.window.getDecorView();
                decor.setVisibility(View.INVISIBLE);
                ViewManager wm = a.getWindowManager();
                WindowManager.LayoutParams l = r.window.getAttributes();
                // 将mDecorView对象赋值给Activity中的mDecor变量,到这里就知道了Activity中的mDecor何时被赋值的了.
                a.mDecor = decor;
                l.type = WindowManager.LayoutParams.TYPE_BASE_APPLICATION;
                l.softInputMode |= forwardBit;
                if (a.mVisibleFromClient) {
                    // 这个变量按照字面意思是窗口是否添加decor,但decorView就是在PhoneWindow中创建的, 
                    // 这个变量的表示是decorView是否展示.
                    a.mWindowAdded = true;
                    // addView最终会调用到ViewRoot.setView(),随后的逻辑就在WMS中了.
                    // 这里就是开始展示decorView了, 很多文章说这里是添加decorView.
                    wm.addView(decor, l);
                }
            } else if (!willBeVisible) {
            }
        } else {
        }
        if (r.activity.mVisibleFromClient) {
            // makeVisible()里面也会执行wm.addView();
            // 但是有个前提条件mWindowAdded变量为false.
            // 所以WindowManager不会重复对decor进行添加展示.
            r.activity.makeVisible();
        }
    }
}