android Window(一)从setConetView说起

Activity的源码

首先从setContentView这里调用的mWindow的 setConetView()

private Window mWindow;
public void setContentView(View view) {
        getWindow().setContentView(view);
        initWindowDecorActionBar();
    }

public Window getWindow() {
    return mWindow;
}

那么这mWindow什么时候初始化？

final void attach(...) {
        attachBaseContext(context);
        mFragments.attachHost(null /*parent*/);
        mWindow = new PhoneWindow(this, window, activityConfigCallback);
        mWindow.setWindowControllerCallback(this);
        mWindow.setCallback(this);
        mWindow.setOnWindowDismissedCallback(this);
        mWindow.getLayoutInflater().setPrivateFactory(this);
        if (info.softInputMode != WindowManager.LayoutParams.SOFT_INPUT_STATE_UNSPECIFIED) {
            mWindow.setSoftInputMode(info.softInputMode);
        }
        if (info.uiOptions != 0) {
            mWindow.setUiOptions(info.uiOptions);
        }
        //...
        //给window设置windowManger
        mWindow.setWindowManager(
           (WindowManager)context.getSystemService(Context.WINDOW_SERVICE),
                mToken, mComponent.flattenToString(),
                (info.flags & ActivityInfo.FLAG_HARDWARE_ACCELERATED) != 0);
        if (mParent != null) {
            mWindow.setContainer(mParent.getWindow());
        }
        mWindowManager = mWindow.getWindowManager();
        mCurrentConfig = config;

        mWindow.setColorMode(info.colorMode);
    }

可以看到这个mWindow 其实是一个PhoneWindow的实例，那么phoneWindow干了什么

可以查看PhoneWindow的源码

152    // This is the view in which the window contents are placed. It is either
153    // mDecor itself, or a child of mDecor where the contents go.
154    private ViewGroup mContentParent;

390    @Override
391    public void setContentView(View view, ViewGroup.LayoutParams params) {
392        // Note: FEATURE_CONTENT_TRANSITIONS may be set in the process of installing the window
393        // decor, when theme attributes and the like are crystalized. Do not check the feature
394        // before this happens.
395        if (mContentParent == null) {
396            installDecor();
397        } else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
398            mContentParent.removeAllViews();
399        }
400
401        if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
402            view.setLayoutParams(params);
403            final Scene newScene = new Scene(mContentParent, view);
404            transitionTo(newScene);
405        } else {
406            mContentParent.addView(view, params);
407        }
408        final Callback cb = getCallback();
409        if (cb != null && !isDestroyed()) {
410            cb.onContentChanged();
411        }
412    }

这里setContentView 主要是 先判断mContentParent是否初始化如果没有初始化调用installDecor 。然后将view添加到mContentParent的ViewGroup中

那么  installDecor  做了些什么

        private DecorView mDecor;
3551    private void installDecor() {
3552        if (mDecor == null) {
3553            mDecor = generateDecor();
3554            mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
3555            mDecor.setIsRootNamespace(true);
3556            if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {
3557                mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);
3558            }
3559        }
3560        if (mContentParent == null) {
3561            mContentParent = generateLayout(mDecor);
3562
3563            // Set up decor part of UI to ignore fitsSystemWindows if appropriate.
3564            mDecor.makeOptionalFitsSystemWindows();
3565
3566            final DecorContentParent decorContentParent = (DecorContentParent) mDecor.findViewById(
3567                    R.id.decor_content_parent);
3568
3569            if (decorContentParent != null) {
3570                mDecorContentParent = decorContentParent;
3571                mDecorContentParent.setWindowCallback(getCallback());
3572                if (mDecorContentParent.getTitle() == null) {
3573                    mDecorContentParent.setWindowTitle(mTitle);
3574                }
3575
3576                final int localFeatures = getLocalFeatures();
3577                for (int i = 0; i < FEATURE_MAX; i++) {
3578                    if ((localFeatures & (1 << i)) != 0) {
3579                        mDecorContentParent.initFeature(i);
3580                    }
3581                }

3582
3583                mDecorContentParent.setUiOptions(mUiOptions);
3584
　　　　　　　　　　　　//setIcon,setLogo ...
3608            } else {
　　　　　　　　　　　　//setTitle ...3627
             }
　　　　　　　　　   　//...
             }
3686    }

installDecor 主要干两件事情

1. 如果mDecor没有初始化generateDecor()初始化
2. 如果mContentParent 没有初始化generateLayout()初始化

generateDecor 就是返回一个新的DecorView

3199    protected DecorView generateDecor() {
3200        return new DecorView(getContext(), -1);
3201    }

这里实例化了DecorView，而DecorView则是PhoneWindow类的一个内部类，继承于FrameLayout，由此可知它也是一个ViewGroup。 
那么DecroView到底充当了什么样的角色呢？ 
其实，DecorView是整个ViewTree的最顶层View，它是一个FrameLayout布局，代表了整个应用的界面。在该布局下面，有标题view和内容view这两个子元素，而内容view则是上面提到的mContentParent

DecorView

 private final class DecorView extends FrameLayout implements RootViewSurfaceTaker{
//...
}

generateLayout()给activity的根布设置各种属性

protected ViewGroup generateLayout(DecorView decor) {
        // Apply data from current theme.
        // 从主题文件中获取样式信息
        TypedArray a = getWindowStyle();

        //...

        if (a.getBoolean(R.styleable.Window_windowNoTitle, false)) {
            requestFeature(FEATURE_NO_TITLE);
        } else if (a.getBoolean(R.styleable.Window_windowActionBar, false)) {
            // Don't allow an action bar if there is no title.
            requestFeature(FEATURE_ACTION_BAR);
        }

        if(...){
            ...
        }

        // Inflate the window decor.
        // 加载窗口布局
        int layoutResource;
        int features = getLocalFeatures();
        // System.out.println("Features: 0x" + Integer.toHexString(features));
        if ((features & (1 << FEATURE_SWIPE_TO_DISMISS)) != 0) {
            layoutResource = R.layout.screen_swipe_dismiss;
        } else if(...){
            ...
        }

        View in = mLayoutInflater.inflate(layoutResource, null);    //加载layoutResource
        decor.addView(in, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT)); //往DecorView中添加子View，即mContentParent
        mContentRoot = (ViewGroup) in;

        ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT); // 这里获取的就是mContentParent
        if (contentParent == null) {
            throw new RuntimeException("Window couldn't find content container view");
        }

        if ((features & (1 << FEATURE_INDETERMINATE_PROGRESS)) != 0) {
            ProgressBar progress = getCircularProgressBar(false);
            if (progress != null) {
                progress.setIndeterminate(true);
            }
        }

        if ((features & (1 << FEATURE_SWIPE_TO_DISMISS)) != 0) {
            registerSwipeCallbacks();
        }

        // Remaining setup -- of background and title -- that only applies
        // to top-level windows.
        //...

        return contentParent;
    }

根据设置的主题样式来设置DecorView的风格，比如说有没有titlebar之类的，接着为DecorView添加子View，而这里的子View则是上面提到的mContentParent，如果上面设置了FEATURE_NO_ACTIONBAR，那么DecorView就只有mContentParent一个子View，所以mContentParent是DecorView本身或者是DecorView的一个子元素。

用一幅图来表示DecorView的结构如下：

小结：DecorView是顶级View，内部有titlebar和contentParent两个子元素，contentParent的id是content，而我们设置的main.xml布局则是contentParent里面的一个子元素。

setConetViewz就是把view 添加到顶层的DecorView里面的contentParent里面

将DecorView添加至Window

每一个Activity组件都有一个关联的Window对象，用来描述一个应用程序窗口。每一个应用程序窗口内部又包含有一个View对象，用来描述应用程序窗口的视图。上文分析了创建DecorView的过程，现在则要把DecorView添加到Window对象中。而要了解这个过程，我们首先要简单先了解一下Activity的创建过程： 
首先，在ActivityThread#handleLaunchActivity中启动Activity，在这里面会调用到Activity#onCreate方法，从而完成上面所述的DecorView创建动作，当onCreate()方法执行完毕，在handleLaunchActivity方法会继续调用到ActivityThread#handleResumeActivity方法，我们看看这个方法的源码：

ActivityThread.java

final void handleResumeActivity(IBinder token, boolean clearHide, boolean isForward) {
    //...
    ActivityClientRecord r = performResumeActivity(token, clearHide); // 这里会调用到onResume()方法

    if (r != null) {
        final Activity a = r.activity;

        //...
        if (r.window == null && !a.mFinished && willBeVisible) {
            r.window = r.activity.getWindow(); // 获得window对象
            View decor = r.window.getDecorView(); // 获得DecorView对象
            decor.setVisibility(View.INVISIBLE);
            ViewManager wm = a.getWindowManager(); // 获得windowManager对象
            WindowManager.LayoutParams l = r.window.getAttributes();
            a.mDecor = decor;
            l.type = WindowManager.LayoutParams.TYPE_BASE_APPLICATION;
            l.softInputMode |= forwardBit;
            if (a.mVisibleFromClient) {
                a.mWindowAdded = true;
                wm.addView(decor, l); // 调用addView方法
            }
            //...
        }
    }
}