Android中Activity和Window和View的關係

關係圖

Android面試中經常會問到Activity和Window、View之間有啥關係？下面先來看一張圖

從上圖可以看出Activity包含Window，Window包含View。

源碼分析

Activity 中

public class Activity extends ContextThemeWrapper
        implements LayoutInflater.Factory2,
        Window.Callback, KeyEvent.Callback,
        OnCreateContextMenuListener, ComponentCallbacks2,
        Window.OnWindowDismissedCallback, WindowControllerCallback,
        AutofillManager.AutofillClient {
	....省略太多代碼
	private Window mWindow;

	   final void attach(Context context, ActivityThread aThread,
            Instrumentation instr, IBinder token, int ident,
            Application application, Intent intent, ActivityInfo info,
            CharSequence title, Activity parent, String id,
            NonConfigurationInstances lastNonConfigurationInstances,
            Configuration config, String referrer, IVoiceInteractor voiceInteractor,
            Window window, ActivityConfigCallback activityConfigCallback) {
        attachBaseContext(context);

        mFragments.attachHost(null /*parent*/);
		// Window類是個抽象類，實現類是PhoneWindow
        mWindow = new PhoneWindow(this, window, activityConfigCallback); 
        mWindow.setWindowControllerCallback(this);
        mWindow.setCallback(this);
        mWindow.setOnWindowDismissedCallback(this);
        mWindow.getLayoutInflater().setPrivateFactory(this);
        ....        
    }
	....
}

從Activity源碼中可以看到，在attach方法中創建了Window的實現類PhoneWindow。

PhoneWindow 中
在PhoneWindow的構造方法中有獲取DecorView

   public PhoneWindow(Context context, Window preservedWindow,
            ActivityConfigCallback activityConfigCallback) {
        this(context);
        // Only main activity windows use decor context, all the other windows depend on whatever
        // context that was given to them.
        mUseDecorContext = true;
        if (preservedWindow != null) {
            mDecor = (DecorView) preservedWindow.getDecorView();
            mElevation = preservedWindow.getElevation();
            mLoadElevation = false;
            mForceDecorInstall = true;
            // If we're preserving window, carry over the app token from the preserved
            // window, as we'll be skipping the addView in handleResumeActivity(), and
            // the token will not be updated as for a new window.
            getAttributes().token = preservedWindow.getAttributes().token;
        }
        // Even though the device doesn't support picture-in-picture mode,
        // an user can force using it through developer options.
        boolean forceResizable = Settings.Global.getInt(context.getContentResolver(),
                DEVELOPMENT_FORCE_RESIZABLE_ACTIVITIES, 0) != 0;
        mSupportsPictureInPicture = forceResizable || context.getPackageManager().hasSystemFeature(
                PackageManager.FEATURE_PICTURE_IN_PICTURE);
        mActivityConfigCallback = activityConfigCallback;
    }

總結

從分析部分源碼中看到

• Activity持有Window對象（實現類是PhoneWindow）.
• PhoneWindow構造方法中獲取DecorView.
• 關係 Activity中包含Window，Window中包含View.