Android T 窗口层级其二 —— 层级结构树的构建（更新中）

如何通过dump中的内容找到对应的代码？
我们dump窗口层级发现会有很多信息，adb shell dumpsys activity containers
这里我们以其中的DefaultTaskDisplayArea为例

在源码的framework目录下查找该字符串，找到对应的代码就可以通过打印堆栈或者搜索代码跟踪的方式找到其调用逻辑

final TaskDisplayArea defaultTaskDisplayArea = 
			new TaskDisplayArea(content, wmService,
			"DefaultTaskDisplayArea", FEATURE_DEFAULT_TASK_CONTAINER);

也就是这一句

当然我们上篇文章也讲到了DisplayContent代表的屏幕的DisplayArea层级结构的根节点，我们可以直接从DisplayContent.java的构造方法出发，追踪其流程

DisplayContent初始化

代码路径：/frameworks/base/services/core/java/com/android/server/wm/DisplayContent.java

/**
     * Create new {@link DisplayContent} instance, add itself to the root window container and
     * initialize direct children.
     * @param display May not be null.
     * @param root {@link RootWindowContainer}
     */
    DisplayContent(Display display, RootWindowContainer root) {
        super(root.mWindowManager, "DisplayContent", FEATURE_ROOT);
        ......
        final Transaction pendingTransaction = getPendingTransaction();
        configureSurfaces(pendingTransaction);
        pendingTransaction.apply();
        ......
    }

创建新的DisplayContent实例，将其自身添加到根窗口容器并初始化直接子级，这里我主要关注一下configureSurfaces(pendingTransaction);

 /**
     * Configures the surfaces hierarchy for DisplayContent
     * This method always recreates the main surface control but reparents the children
     * if they are already created.
     * @param transaction as part of which to perform the configuration
     */
    private void configureSurfaces(Transaction transaction) {
        final SurfaceControl.Builder b = mWmService.makeSurfaceBuilder(mSession)
                .setOpaque(true)
                .setContainerLayer()
                .setCallsite("DisplayContent");
        mSurfaceControl = b.setName(getName()).setContainerLayer().build();

        if (mDisplayAreaPolicy == null) {
            // Setup the policy and build the display area hierarchy.
            // Build the hierarchy only after creating the surface so it is reparented correctly
            mDisplayAreaPolicy = mWmService.getDisplayAreaPolicyProvider().instantiate(
                    mWmService, this /* content */, this /* root */,
                    mImeWindowsContainer);
        }
        ......
       
    }

通过DisplayContent来配置图层结构

DisplayAreaPolicy初始化

/frameworks/base/services/core/java/com/android/server/wm/DisplayAreaPolicy.java

mDisplayAreaPolicy = mWmService.getDisplayAreaPolicyProvider().instantiate(
        mWmService, this /* content */, this /* root */,
        mImeWindowsContainer)

调用DisplayAreaPolicy中的Provider接口instantiate方法，去初始化一个DisplayArea层级结构

DisplayAreaPolicy.Provider

    /**
     * Provider for {@link DisplayAreaPolicy} instances.
     *
     * 
By implementing this interface and overriding the
     * {@code config_deviceSpecificDisplayAreaPolicyProvider}, a device-specific implementations
     * of {@link DisplayAreaPolicy} can be supplied.
     */
    public interface Provider {
        /**
         * Instantiates a new {@link DisplayAreaPolicy}. It should set up the {@link DisplayArea}
         * hierarchy.
         *
         * @see DisplayAreaPolicy#DisplayAreaPolicy
         */
        DisplayAreaPolicy instantiate(WindowManagerService wmService, DisplayContent content,
                RootDisplayArea root, DisplayArea.Tokens imeContainer);

用来实例化一个DisplayAreaPolicy对象，这个对象应该建立起DisplayArea层级结构，实际走到的则是DisplayAreaPolicy.Provider的实现类DisplayAreaPolicy.DefaultProvider.instantiate方法

DisplayAreaPolicy.DefaultProvider

 /** Provider for platform-default display area policy. */
    static final class DefaultProvider implements DisplayAreaPolicy.Provider {
        @Override
        public DisplayAreaPolicy instantiate(WindowManagerService wmService,
                DisplayContent content, RootDisplayArea root,
                DisplayArea.Tokens imeContainer) {
             //1.创建一个名为“DefaultTaskDisplayArea”的TaskDisplayArea,并将其添加到List中
            final TaskDisplayArea defaultTaskDisplayArea = new TaskDisplayArea(content, wmService,
                    "DefaultTaskDisplayArea", FEATURE_DEFAULT_TASK_CONTAINER);
            final List<TaskDisplayArea> tdaList = new ArrayList<>();
            tdaList.add(defaultTaskDisplayArea);

            // Define the features that will be supported under the root of the whole logical
            // display. The policy will build the DisplayArea hierarchy based on this.
            //2.创建HierarchyBuilder
            final HierarchyBuilder rootHierarchy = new HierarchyBuilder(root);
            // Set the essential containers (even if the display doesn't support IME).
            //3.1添加ImeContainer到HierarchyBuilder
            //3.2创建并保存默认TaskDisplayArea到HierarchyBuilder
            rootHierarchy.setImeContainer(imeContainer).setTaskDisplayAreas(tdaList);
            if (content.isTrusted()) {
                // Only trusted display can have system decorations.
                //4.为HierarchyBuilder添加Feature
                configureTrustedHierarchyBuilder(rootHierarchy, wmService, content);
            }

            // Instantiate the policy with the hierarchy defined above. This will create and attach
            // all the necessary DisplayAreas to the root.
            //5.生成DisplayArea层级结构
            return new DisplayAreaPolicyBuilder().setRootHierarchy(rootHierarchy).build(wmService);
        }

这里DefaultProvider实现了这个接口。
这个方法主要干了这几件事情：
1.创建一个名为“DefaultTaskDisplayArea”的TaskDisplayArea,并将其添加到List中
2.创建HierarchyBuilder
3.1添加ImeContainer到HierarchyBuilder
3.2添加TaskDisplayArea到HierarchyBuilder
4.为HierarchyBuilder添加Feature
5.生成DisplayArea层级结构