Android的Activity视图层级分析

Activity视图层级图

Activity的初始化
Activity的初始化是从从Activity的setContentView()，源码为

    public void setContentView(View view) {
        getWindow().setContentView(view);
        initWindowDecorActionBar();
    }
    public void setContentView(@LayoutRes int layoutResID) {
        getWindow().setContentView(layoutResID);
        initWindowDecorActionBar();
    }
        public void setContentView(View view, ViewGroup.LayoutParams params) {
        getWindow().setContentView(view, params);
        initWindowDecorActionBar();
    }

三种重载方法，都有调用initWindowDecorActionBar()为显示Decor和ActionBar

    private void initWindowDecorActionBar() {
        //window是抽象类，所以找其实现类phoneWindow
        Window window = getWindow();

        //初始化decorview
        window.getDecorView();

        if (isChild() || !window.hasFeature(Window.FEATURE_ACTION_BAR) || mActionBar != null) {
            return;
        }
        //新建actionbar
        mActionBar = new WindowDecorActionBar(this);
        mActionBar.setDefaultDisplayHomeAsUpEnabled(mEnableDefaultActionBarUp);
        //设置actionbar的图标
        mWindow.setDefaultIcon(mActivityInfo.getIconResource());
        mWindow.setDefaultLogo(mActivityInfo.getLogoResource());
    }

PhoneWindow的实现类

    public void setContentView(int layoutResID) {
        // Note: FEATURE_CONTENT_TRANSITIONS may be set in the process of installing the window
        // decor, when theme attributes and the like are crystalized. Do not check the feature
        // before this happens.
        if (mContentParent == null) {
        //初始化decor
            installDecor();
        } else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
            mContentParent.removeAllViews();
        }

        if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
            final Scene newScene = Scene.getSceneForLayout(mContentParent, layoutResID,
                    getContext());
            transitionTo(newScene);
        } else {
            mLayoutInflater.inflate(layoutResID, mContentParent);
        }
        mContentParent.requestApplyInsets();
        final Callback cb = getCallback();
        if (cb != null && !isDestroyed()) {
            cb.onContentChanged();
        }
    }

初始化DecorView代码

 private void installDecor() {
        if (mDecor == null) {
            mDecor = generateDecor();
            mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
            mDecor.setIsRootNamespace(true);
            if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {
                mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);
            }
        }

        if (mContentParent == null) {
            mContentParent = generateLayout(mDecor);

            // Set up decor part of UI to ignore fitsSystemWindows if appropriate.
            mDecor.makeOptionalFitsSystemWindows();

            final DecorContentParent decorContentParent = (DecorContentParent) mDecor.findViewById(
                    R.id.decor_content_parent);

            if (decorContentParent != null) {
                mDecorContentParent = decorContentParent;
                mDecorContentParent.setWindowCallback(getCallback());
                if (mDecorContentParent.getTitle() == null) {
                    mDecorContentParent.setWindowTitle(mTitle);
                }

最后Activity的视图层级为

再做一次反向操作，从DecorView中Remove。一步一步来看看取消了什么。

getDecorView(activity)..removeViewAt(decor.getChildCount() - 1)

    public void removeViewAt(int index) {
        //查看这个方法
        removeViewInternal(index, getChildAt(index));
        requestLayout();
        invalidate(true);
    }

    public View getChildAt(int index) {
        if (index < 0 || index >= mChildrenCount) {
            return null;
        }
        return mChildren[index];
    }

Ctrl+U 分别计算mChildren[0],mChildren[1],mChildren[2]的getleft,getright,gettop,getbottom的值。

mChildren[2]是最上方的状态条的视图。
mChildren[1]是最底部的导航条的视图。
mChildren[0]是背景整个视图。

注：国产手机不一定能看到。
参考文章：http://blog.csdn.net/mr_liabill/article/details/49534851

可通过对Activity视图层级的研究，将浮窗灵活运用。

http://www.jianshu.com/p/b4c23dee9206
http://www.jianshu.com/p/50fbec2baeb4