Activity的setContentView渲染的原理

Posted 2022-12-14 花姓-老花

通过源码得知Activity、PhoneWindow和Window之间的关系（API25）

PhoneWindow是唯一实现Window的具体实现类，在PhoneWindow中有一个DecorView对象

DecorView对象是所有应用窗口（即Activity界面）的根View，DecorView是FrameLayout的子类，对FrameLayout进行装饰或渲染，是所有应用窗口的根View

setContentView

Activity中setContentView直接调用getWindow().setContentView()，PhoneWindow又是Window的实现类，所以就来具体看PhoneWindow的setContentView方法

setContentView(int layoutResID)源码

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)  //mContentParent是放置窗口内容（Activity界面）的视图，如果mContentParent为空
            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();
        
        mContentParentExplicitlySet = true;
    

上面知道，如果mContentParent为空时，就调用installDecor来生成mContentParent的View（即是Activity界面的根视图）

加载完布局视图后，最后onContentChanged方法，发现在PhoneWindow并没重写Window的这个方法，onContentChange方法在Window中是空方法

public void onContentChanged();

当Activity的布局改动时，即setContentView()或者addContentView()方法执行完毕时就会调用该方法。

private void installDecor() 
        mForceDecorInstall = false;
        if (mDecor == null)    //mDecor是个顶层视图
            mDecor = generateDecor(-1);
            mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
            mDecor.setIsRootNamespace(true);
            if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) 
                mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);
            
         else 
            mDecor.setWindow(this);
        
        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);
                

                final int localFeatures = getLocalFeatures();
                for (int i = 0; i < FEATURE_MAX; i++) 
                    if ((localFeatures & (1 << i)) != 0) 
                        mDecorContentParent.initFeature(i);
                    
                

                mDecorContentParent.setUiOptions(mUiOptions);

                if ((mResourcesSetFlags & FLAG_RESOURCE_SET_ICON) != 0 ||
                        (mIconRes != 0 && !mDecorContentParent.hasIcon())) 
                    mDecorContentParent.setIcon(mIconRes);
                 else if ((mResourcesSetFlags & FLAG_RESOURCE_SET_ICON) == 0 &&
                        mIconRes == 0 && !mDecorContentParent.hasIcon()) 
                    mDecorContentParent.setIcon(
                            getContext().getPackageManager().getDefaultActivityIcon());
                    mResourcesSetFlags |= FLAG_RESOURCE_SET_ICON_FALLBACK;
                
                if ((mResourcesSetFlags & FLAG_RESOURCE_SET_LOGO) != 0 ||
                        (mLogoRes != 0 && !mDecorContentParent.hasLogo())) 
                    mDecorContentParent.setLogo(mLogoRes);
                

                // Invalidate if the panel menu hasn't been created before this.
                // Panel menu invalidation is deferred avoiding application onCreateOptionsMenu
                // being called in the middle of onCreate or similar.
                // A pending invalidation will typically be resolved before the posted message
                // would run normally in order to satisfy instance state restoration.
                PanelFeatureState st = getPanelState(FEATURE_OPTIONS_PANEL, false);
                if (!isDestroyed() && (st == null || st.menu == null) && !mIsStartingWindow) 
                    invalidatePanelMenu(FEATURE_ACTION_BAR);
                
             else 
                mTitleView = (TextView) findViewById(R.id.title);
                if (mTitleView != null) 
                    if ((getLocalFeatures() & (1 << FEATURE_NO_TITLE)) != 0) 
                        final View titleContainer = findViewById(R.id.title_container);
                        if (titleContainer != null) 
                            titleContainer.setVisibility(View.GONE);
                         else 
                            mTitleView.setVisibility(View.GONE);
                        
                        mContentParent.setForeground(null);
                     else 
                        mTitleView.setText(mTitle);
                    
                
            

           .......
          
            
        
    

上面知道，如果mContentParent 为空，通过generateLayout(mDecor)进行赋值，参数mDecor是Activity顶层布局（也可以理解为一个ViewGroup）视图

protected ViewGroup generateLayout(DecorView decor) 
        // Apply data from current theme.

        TypedArray a = getWindowStyle();   //mCurrentParent（ViewGroup）装饰的风格

        .....
        

        WindowManager.LayoutParams params = getAttributes();   //设置布局相关属性

        // Non-floating windows on high end devices must put up decor beneath the system bars and
        // therefore must know about visibility changes of those.  设置相关设备非浮动窗口的显示情况
        if (!mIsFloating && ActivityManager.isHighEndGfx()) 
            if (!targetPreL && a.getBoolean(
                    R.styleable.Window_windowDrawsSystemBarBackgrounds,
                    false)) 
                setFlags(FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS,
                        FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS & ~getForcedWindowFlags());
            
            if (mDecor.mForceWindowDrawsStatusBarBackground) 
                params.privateFlags |= PRIVATE_FLAG_FORCE_DRAW_STATUS_BAR_BACKGROUND;
            
        
       .....

        

        // Inflate the window decor.

        int layoutResource;   //布局xml资源
        int features = getLocalFeatures(); //得到此窗口正常工作的特性。给出了requestfeature()集，被处理的只有这个窗口本身，而不它的容器
        ......
        mDecor.startChanging(); //标记顶层DecorView开始改变
        mDecor.onResourcesLoaded(mLayoutInflater, layoutResource);  //得到上面设置的xml Layout资源，然后添加到DecorView根视图上

        ViewGroup contentParent = (ViewGroup)findViewById(ID_android_CONTENT);
        if (contentParent == null) 
            throw new RuntimeException("Window couldn't find content container view");
        

       	....... //DecorView相关属性设置
        mDecor.finishChanging();

        return contentParent;
    

上面主要根据窗口风格类型选择不窗口的根布局文件，mDecor做为根视图将该窗口根布局添加进去，然后获取id为ID_ANDROID_CONTENT，然后返回给mContentParent对象，从上面就知道installDecor方法实质就是产生mDecor和mContentParent对象

在Activity中设置标题状态（feature）或者相关主题（theme），有两种配置方式

1、通过xml形式android:theme属性，通过这里的getWindowStyle()获取的

2、通过代码形式requestWindowFeature()，在这里通过getLocalFeature()获取的

设置Activity的属性时必须在setContentView方法之前调用requestFeature()方法的原因

setContentView方法工作流程：

Activity的setContentView主要是把Activity布局文件（xml或代码形式）添加到顶层视图上

1、先创建一个DecorView对象mDecor作为所有应用窗口（即Activity界面）的根视图

2、根据不同Feature等风格选择不同窗口修饰布局文件

3、将Activity布局文件添加到mContentParent上

public void setContentView(int layoutResID) 
        ......
        if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) 
            final Scene newScene = Scene.getSceneForLayout(mContentParent, layoutResID,
                    getContext());
            transitionTo(newScene);
         else 
            mLayoutInflater.inflate(layoutResID, mContentParent);
        
       ......