Window和WindowManager

àì夳堔傛蜴生んèń 2023-10-17 10:17 4阅读 0赞

## Window和WindowManager ##

Window是一个抽象的概念，每一个Window都对应一个View和一个ViewRootImpl，Window和View通过ViewRootImpl来建立联系。

在实际使用中无法直接访问Window，对Window的访问必须通过Windowmanager。

Window实际上是View的直接管理者

Android中所有的视图都是通过Window来呈现的，不管是Activity、Dialog还是Toast，它们的视图实际上是附加在Window上的。

### Window的类型 ###

#### 应用Window ####

对应着一个Activity

#### 子Window ####

子Window不能单独存在，它需要附属在特定的父Window之中，比如Dialog

#### 系统Window ####

需要声明权限才能创建的Window，比如Toast和系统状态栏

### Window的层级 ###

层级大的Window会覆盖层级小的Window，层级对应于WindowManager.LayoutParams的type参数。

应用Window层级范围:1~999  
子Window的层级范围:1000~1999  
系统Window的层级范围:2000~2999

### WindowManger ###

Window通过WindowManager来访问，WindowManager是一个接口，它的真正实现是WindowManagerImpl。而WindowmanagerImpl的增删更新View都交由WindowManagerGlobal来处理。

public final class WindowManagerImpl implements WindowManager {
        private final WindowManagerGlobal mGlobal = WindowManagerGlobal.getInstance();
    
        @Override
        public void addView(View view, ViewGroup.LayoutParams params) {
            mGlobal.addView(view, params, mDisplay, mParentWindow);
        }
    
        @Override
        public void updateViewLayout(View view, ViewGroup.LayoutParams params) {
            mGlobal.updateViewLayout(view, params);
        }
    
        @Override
        public void removeView(View view) {
            mGlobal.removeView(view, false);
        }
    }

需要了解的WindowManagerGlobal的几个重要的参数

//存储所有Window所对应的View
    private final ArrayList<View> mViews = new ArrayList<View>();
    //存储所有Window所对应的ViewRootImpl
    private final ArrayList<ViewRootImpl> mRoots = new ArrayList<ViewRootImpl>();
    //存储所有Window所对应的布局参数
    private final ArrayList<WindowManager.LayoutParams> mParams =
            new ArrayList<WindowManager.LayoutParams>();
    //存储即将被删除的View对象 (已经调用removeView方法但是删除操作还未完成的Window对象)
    private final ArraySet<View> mDyingViews = new ArraySet<View>();

### Window的添加过程 ###

Window的添加过程通过WindowManager的addView来实现

WindowManagerGlobal的addView()

#### 1.检查参数是否合法，如果是子Window那么还需要调整一些布局参数 ####

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");
    }
    
    final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams)params;
    if (parentWindow != null) {
        parentWindow.adjustLayoutParamsForSubWindow(wparams);
    }

#### 2.创建ViewRootImpl并将View添加到列表中 ####

root = new ViewRootImpl(view.getContext(), display);
    
    view.setLayoutParams(wparams);
    
    mViews.add(view);
    mRoots.add(root);
    mParams.add(wparams);

#### 3.通过ViewRootImpl来更新界面并完成window的添加过程 ####

//setView->requestLayout-> ... -> performTraversals -> 开始measure、layout、draw三大流程
    root.setView(view, wparams, panelParentView);

在来看ViewRootImpl\#setView()，Window的添加请求最终交给WindowManagerService处理。

public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
            //...           
    
            //[重要方法] requestLayout-> ... -> performTraversals -> 开始measure、layout、draw三大流程
            requestLayout();
    
            //...
    
            try {
                //通过WindowSession最终完成Window的添加
                //mWindowSession是IWindowSession，它是一个Binder对象 [IPC调用]
                //mWindowSession.addToDisplay -> WindowmanagerService.addWindow
                mOrigWindowType = mWindowAttributes.type;
                mAttachInfo.mRecomputeGlobalAttributes = true;
                collectViewAttributes();
                res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
                        getHostVisibility(), mDisplay.getDisplayId(),
                        mAttachInfo.mContentInsets, 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);
            }
        //...
    }

### WIndow的删除过程 ###

public void removeView(View view, boolean immediate) {
        if (view == null) {
            throw new IllegalArgumentException("view must not be null");
        }
    
        synchronized (mLock) {
            int index = findViewLocked(view, true);
            View curView = mRoots.get(index).getView();
            //通过index查找待删除的View
            removeViewLocked(index, immediate);
            if (curView == view) {
                return;
            }
    
            throw new IllegalStateException("Calling with view " + view
                    + " but the ViewAncestor is attached to " + curView);
        }
    }

再来看removeViewLocked

private void removeViewLocked(int index, boolean immediate) {
        ViewRootImpl root = mRoots.get(index);
        View view = root.getView();
    
        if (view != null) {
            InputMethodManager imm = InputMethodManager.getInstance();
            if (imm != null) {
                imm.windowDismissed(mViews.get(index).getWindowToken());
            }
        }
        具体的删除操作
        boolean deferred = root.die(immediate);
        if (view != null) {
            view.assignParent(null);
            if (deferred) {
                mDyingViews.add(view);
            }
        }
    }

再来看die方法。如果是同步删除，立即调用doDie()，如果是异步调用，会通过Handler发送消息调用doDie()。

boolean die(boolean immediate) {
        // Make sure we do execute immediately if we are in the middle of a traversal or the damage
        // done by dispatchDetachedFromWindow will cause havoc on return.
        //立即删除 -> 同步删除 (不推荐，容易发生意外)
        if (immediate && !mIsInTraversal) {
            doDie();
            return false;
        }
    
        if (!mIsDrawing) {
            destroyHardwareRenderer();
        } else {
            Log.e(TAG, "Attempting to destroy the window while drawing!\n" +
                    "  window=" + this + ", title=" + mWindowAttributes.getTitle());
        }
        //异步删除
        mHandler.sendEmptyMessage(MSG_DIE);
        return true;
    }

再来看doDie()

void doDie() {
        //...
        //真正删除View
        dispatchDetachedFromWindow();
        //...
    }

dispatchDetachedFromWindow主要做4件事

1.  垃圾回收相关的工作，比如清除数据和消息，移除回调。
2.  通过Session的remove方法删除Window:mWindowSession.remove(mWindow)，这同样是一个IPC过程，最终会调用WindowManagerService的removeWindow方法。
3.  调用View的dispatchDetachedFromWindow方法，在内部会调用View的onDetachedFromWindow()以及onDetachedFromWindowInternal()。
4.  调用WindowManagerGlobal的doRemoveView方法刷新数据，包括mRoots、mParams以及mDyingViews，需要将当前Window所关联的这三个对象从列表中删除。

> onDetachedFromWindow()  
> 当View从Window中移除时，这个方法就会被调用。  
> 可以在这个方法内部做一个资源回收工作，比如终止动画、停止线程。

### Window的更新过程 ###

public void updateViewLayout(View view, ViewGroup.LayoutParams params) {
        if (view == null) {
            throw new IllegalArgumentException("view must not be null");
        }
        if (!(params instanceof WindowManager.LayoutParams)) {
            throw new IllegalArgumentException("Params must be WindowManager.LayoutParams");
        }
    
        final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams)params;
    
        view.setLayoutParams(wparams);
    
        synchronized (mLock) {
            int index = findViewLocked(view, true);
            ViewRootImpl root = mRoots.get(index);
            mParams.remove(index);
            mParams.add(index, wparams);
            //更新LayoutParams -> scheduleTraversals -> ... -> 开始measure、layout、draw三大流程
            root.setLayoutParams(wparams, false);
        }
    }

window的更新通过WindowManagerGlobal\#updateViewLayout()来完成，内部通过调用VIewRootImpl的setLayoutParams()，然后经过一些列的方法，最终会开始measure、layout、draw三大流程，从而实现window的更新。

#### 其他 ####

> 参考 《Android艺术开发探索》