Window, WindowManager, WindowManagerService 的简单梳理（一）

Window, WindowManager, WindowManagerService 的简单梳理（三）- Activiy 的 Window 的创建过程

通过 Window, WindowManager, WindowManagerService 的简单梳理（一） 已经知道，我们能够从 Activity 或者 Context 拿到的，就是 WindowManager 的具体实现 WindowManagerImpl。
当我们想要添加一个 Window 的时候，就是要通过 WindowManagerImpl 的方法来实现。更准确的说，是 WindowManagerImpl 实现的 ViewManager 接口的方法。

public interface ViewManager
{
    /**
     * Assign the passed LayoutParams to the passed View and add the view to the window.
     * <p>Throws {@link android.view.WindowManager.BadTokenException} for certain programming
     * errors, such as adding a second view to a window without removing the first view.
     * <p>Throws {@link android.view.WindowManager.InvalidDisplayException} if the window is on a
     * secondary {@link Display} and the specified display can't be found
     * (see {@link android.app.Presentation}).
     * @param view The view to be added to this window.
     * @param params The LayoutParams to assign to view.
     */
    public void addView(View view, ViewGroup.LayoutParams params);
    public void updateViewLayout(View view, ViewGroup.LayoutParams params);
    public void removeView(View view);
}

下面的例子是参考任玉刚的《Android 开发艺术探索》，我做了一点修改。

        Button btn = new Button(this);
        btn.setText("WMS Demo");

        WindowManager.LayoutParams params = new WindowManager.LayoutParams(WindowManager.LayoutParams.WRAP_CONTENT, WindowManager.LayoutParams.WRAP_CONTENT,
                1, 0, PixelFormat.TRANSPARENT);
        params.flags = WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL | WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE | WindowManager.LayoutParams.FLAG_SHOW_WALLPAPER;
        params.gravity = Gravity.LEFT | Gravity.TOP;
        params.x = 100;
        params.y = 100;
        getWindowManager().addView(btn, params);

其中，WindowManager.LayoutParams 的 type 和 flags 两个参数比较重要，大家可以参考网上的各种说明。当然，源码里面也有详细的说明。
我这个例子，是可以直接在 activity 里面跑起来的，作用是在屏幕上坐标为 params.x = 100; params.y = 100; 的地方添加一个按钮。

下面，我们就跟着源码看看，调用 getWindowManager().addView(btn, params) 后到底发生了什么。

Window 的添加过程

// WindowManagerImpl 
public final class WindowManagerImpl implements WindowManager {
    ...
    private final WindowManagerGlobal mGlobal = WindowManagerGlobal.getInstance();
    ...
    @Override
    public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
        applyDefaultToken(params);
        mGlobal.addView(view, params, mContext.getDisplay(), mParentWindow);
    }
    ...
}

可见，WindowManagerImpl 把任务转给了 mGlobal 的 addView 方法。
看下面的代码，再往下走，就进入了root.setView(view, wparams, panelParentView)，也就是 ViewRootImpl 的方法。

// WindowManagerGlobal 
public final class WindowManagerGlobal {
    ...
    // 存储所有 Window 对应的 View
    private final ArrayList<View> mViews = new ArrayList<View>();
    // 存储所有 Window 对应的 ViewRootImpl
    private final ArrayList<ViewRootImpl> mRoots = new ArrayList<ViewRootImpl>();
    // 存储所有 Window 对应的布局参数
    private final ArrayList<WindowManager.LayoutParams> mParams =
            new ArrayList<WindowManager.LayoutParams>();
    // 存储正在被删除的 View 对象，也就是调用了 removeView 方法，但是删除操作还未完成的 View
    private final ArraySet<View> mDyingViews = new ArraySet<View>();

    ...

    public void addView(View view, ViewGroup.LayoutParams params,
            Display display, Window parentWindow) {
        if (view == null) {
            throw new IllegalArgumentException("view must not be null");
        }
        if (display == null) {
            throw new IllegalArgumentException("display must not be null");
        }
        if (!(params instanceof WindowManager.LayoutParams)) {
            throw new IllegalArgumentException("Params must be WindowManager.LayoutParams");
        }

        ...

        ViewRootImpl root;
        View panelParentView = null;
        ...
            root = new ViewRootImpl(view.getContext(), display);

            view.setLayoutParams(wparams);

            mViews.add(view);
            mRoots.add(root);
            mParams.add(wparams);
        }

        // do this last because it fires off messages to start doing things
        try {
            root.setView(view, wparams, panelParentView);
        } catch (RuntimeException e) {
            // BadTokenException or InvalidDisplayException, clean up.
            synchronized (mLock) {
                final int index = findViewLocked(view, false);
                if (index >= 0) {
                    removeViewLocked(index, true);
                }
            }
            throw e;
        }
    }
}

ViewRootImpl 的 setView 会最终调用到 mWindowSession.addToDisplay()。

// ViewRootImpl 
public final class ViewRootImpl implements ViewParent,
        View.AttachInfo.Callbacks, ThreadedRenderer.HardwareDrawCallbacks {
    ...
    final IWindowSession mWindowSession;

    final W mWindow;
    ...
    public ViewRootImpl(Context context, Display display) {
        mContext = context;
        mWindowSession = WindowManagerGlobal.getWindowSession();

        mWindow = new W(this);
        ...
    }
    ...

    public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
        synchronized (this) {
            ...
            int res; /* = WindowManagerImpl.ADD_OKAY; */

                // Schedule the first layout -before- adding to the window
                // manager, to make sure we do the relayout before receiving
                // any other events from the system.
                requestLayout();
                ...
                try {
                    mOrigWindowType = mWindowAttributes.type;
                    mAttachInfo.mRecomputeGlobalAttributes = true;
                    collectViewAttributes();
                    res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
                            getHostVisibility(), mDisplay.getDisplayId(),
                            mAttachInfo.mContentInsets, mAttachInfo.mStableInsets,
                            mAttachInfo.mOutsets, mInputChannel);
                } catch (RemoteException e) {
                    mAdded = false;
                    mView = null;
                    mAttachInfo.mRootView = null;
                    mInputChannel = null;
                    mFallbackEventHandler.setView(null);
                    unscheduleTraversals();
                    setAccessibilityFocus(null, null);
                    throw new RuntimeException("Adding window failed", e);
                } finally {
                    if (restore) {
                        attrs.restore();
                    }
                }
        }
    }
    ...
    @Override
    public void requestLayout() {
        if (!mHandlingLayoutInLayoutRequest) {
            checkThread();
            mLayoutRequested = true;
            // scheduleTraversals 是 View 绘制的入口
            scheduleTraversals();
        }
    }

    ...

    static class W extends IWindow.Stub {
        private final WeakReference<ViewRootImpl> mViewAncestor;
        private final IWindowSession mWindowSession;

        W(ViewRootImpl viewAncestor) {
            mViewAncestor = new WeakReference<ViewRootImpl>(viewAncestor);
            mWindowSession = viewAncestor.mWindowSession;
        }
        ...
    }
}

mWindowSession 的类型是 IWindowSession，它是一个 Binder 对象，真正的实现类是 Session，这是一次 IPC 调用。
我在 Window, WindowManager, WindowManagerService 的简单梳理（一） 中曾经写过，WindowManagerService 是 IWindowManager 接口的实现。所以，这里才会和 WindowManagerService 发生关系。

// WindowManagerGlobal
    public static IWindowSession getWindowSession() {
        synchronized (WindowManagerGlobal.class) {
            if (sWindowSession == null) {
                try {
                    InputMethodManager imm = InputMethodManager.getInstance();
                    IWindowManager windowManager = getWindowManagerService();
                    sWindowSession = windowManager.openSession(
                            new IWindowSessionCallback.Stub() {
                                @Override
                                public void onAnimatorScaleChanged(float scale) {
                                    ValueAnimator.setDurationScale(scale);
                                }
                            },
                            imm.getClient(), imm.getInputContext());
                } catch (RemoteException e) {
                    throw e.rethrowFromSystemServer();
                }
            }
            return sWindowSession;
        }
    }

// Session 
final class Session extends IWindowSession.Stub
                    implements IBinder.DeathRecipient {
    final WindowManagerService mService;
    ...
    public Session(WindowManagerService service, IWindowSessionCallback callback,
            IInputMethodClient client, IInputContext inputContext) {
        mService = service;
        ...
    }
    ...
    @Override
    public int addToDisplay(IWindow window, int seq, WindowManager.LayoutParams attrs,
            int viewVisibility, int displayId, Rect outContentInsets, Rect outStableInsets,
            Rect outOutsets, InputChannel outInputChannel) {
        return mService.addWindow(this, window, seq, attrs, viewVisibility, displayId,
                outContentInsets, outStableInsets, outOutsets, outInputChannel);
    }
}

可见，mWindowSession 内部最终是将 Window 提交给了 WindowManagerService 去处理。WindowManagerService 内部会为每一个应用保留一个单独的 Session。

如果再仔细看，mWindowSession 提交的是一个 IWindow 对象，也就是 ViewRootImpl 内部的 mWindow对象，类型是 ViewRootImpl.W。

所以说，什么是 Window？如果 Window 是指用来做显示的一个抽象概念。那么，当一个新的 Window 被添加以后，WindowManagerService 中会增加一个 IWindow 对象。

值得一提的是，Activity 的 Window 的创建，也基本遵循这个过程，只不过这个过程是自动完成的。