Android之Window与WindowManager

基本概念

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• Window、PhoneWindow

顶层窗口样式和行为的抽象类, 概括了Android窗口的基本属性和基本功能。该类实例的getDecorView()方法返回的DecorView被用来作为顶层视图添加到WM中。

创建时机:

ActivityThread.handleLaunchActivity —> ActivityThread.performLaunchActivity —> Activity.attach

• WindowManager、WindowManagerImpl、WindowManagerGlobal

WindowManager与一个特定的Display相关联

• WindowManagerService

对系统中的所有窗口进行管理。WindowManager是运行在Application process中的, WindowManagerService是在system_server进程中运行, 两者的通信是通过中间的会话层IWindowSession来进行的。

添加一个根View到WindowManager中

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{    final WindowManager wm = (WindowManager)getSystemService(Context.WINDOW_SERVICE);    WindowManager.LayoutParams lp = new WindowManager.LayoutParams(                wm.getDefaultDisplay().getWidth(),wm.getDefaultDisplay().getHeight());    lp.type = WindowManager.LayoutParams.TYPE_APPLICATION;    lp.flags = WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE;    lp.format = PixelFormat.TRANSLUCENT;    wm.addView(maskView, lp);}

相关类简化结构

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public class PhoneWindow extends Window{    private DecorView mDecor;}public interface ViewManager{    public void addView(View view, ViewGroup.LayoutParams params);    public void updateViewLayout(View view, ViewGroup.LayoutParams params);    public void removeView(View view);}public interface WindowManager extends ViewManager {    public static class LayoutParams extends ViewGroup.LayoutParams{        //X position for this window        public int x;        public int y;        public int type;        public int flags;    }}public final class WindowManagerImpl implements WindowManager {    private final WindowManagerGlobal mGlobal = WindowManagerGlobal.getInstance();    private final Display mDisplay;    public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {        mGlobal.addView(view, params, mDisplay, mParentWindow);    }}public final class WindowManagerGlobal {    //表示View树的根节点    private final ArrayList<View> mViews = new ArrayList<View>();    //表示ViewRootImpl,一个根view对应一个ViewRootImpl    private final ArrayList<ViewRootImpl> mRoots = new ArrayList<ViewRootImpl>();    //表示根view的WindowManager.LayoutParams    private final ArrayList<WindowManager.LayoutParams> mParams =         new ArrayList<WindowManager.LayoutParams>();    public void addView(View view, ViewGroup.LayoutParams params,Display display, Window parentWindow) {         final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams) params;         ...         ViewRootImpl root = new ViewRootImpl(view.getContext(), display);         view.setLayoutParams(wparams);        mViews.add(view);        mRoots.add(root);        mParams.add(wparams);        ...        //通过ViewRootImpl来更新界面并完成Window的添加过程        root.setView(view, wparams, panelParentView);    }}public final class ViewRootImpl implements ViewParent{   public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {        //1、完成异步刷新请求，重绘界面        requestLayout();        ...        //2、通过WindowSession最终完成window的添加过程, WindowSession内部通过        //WindowManagerService来实现Window的添加        int res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,                            getHostVisibility(), mDisplay.getDisplayId(),                            mAttachInfo.mContentInsets, mAttachInfo.mStableInsets,                            mAttachInfo.mOutsets, mInputChannel);   }}

Window的创建过程

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Activity对应的PhoneWindow创建过程及添加时机

首先看下ActivityThead中的两个重要的方法：

       performLaunchActivity( );       handleResumeActivity( );

创建时机：

在performLaunchActivity中，会调用activity.attach方法建立一个window。

Activity的View附属到Window上：setContentView()

添加时机：

在handleResumeActivity方法中启动activity的时候，首先会调用Activity的onResume方法，接着调用Activity的makeVisible方法,在该方法中将主窗口加入到WindowManager中

代码如下：

void makeVisible() {    if (!mWindowAdded) {        ViewManager wm = getWindowManager();        //实际上是把主窗口的顶级view加入到WindowMangaer        wm.addView(mDecor, getWindow().getAttributes());        mWindowAdded = true;    }    mDecor.setVisibility(View.VISIBLE);}

Dialog的Window创建过程

1. 创建窗口：构造函数中
2. 初始化DecorView并将Dialog的View添加到DecorView中：setContentView（）
3. 将DecorView添加到Window中并显示：show（）

public class Dialog implements DialogInterface, ... {    Dialog(Context context,int themeResId, boolean createContextThemeWrapper) {        if (createContextThemeWrapper) {            mContext = new ContextThemeWrapper(context, themeResId);        } else {            mContext = context;        }        mWindowManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);        final Window w = new PhoneWindow(mContext);        mWindow = w;        w.setCallback(this);        w.setOnWindowDismissedCallback(this);        w.setWindowManager(mWindowManager, null, null);        w.setGravity(Gravity.CENTER);        mListenersHandler = new ListenersHandler(this);    }    public void setContentView(@LayoutRes int layoutResID) {        mWindow.setContentView(layoutResID);    }    public void show() {        mDecor = mWindow.getDecorView();        mWindowManager.addView(mDecor, l);    }}

Window添加过程

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实际上是根视图的添加过程，在WindowManager层已经没有Window的概念，Window的概念存在于UI层，是对于Activity、Dialog、Toast等而言的。

1. WindowManager.addView()：调用2
2. WindowManagerGlobal.addView():
   
   1. 创建ViewRootImpl
   2. 调用3
3. ViewRootImpl.setView()：
   
   1. requestLayout()
   2. mWindowSession.addToDisplay

总结

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通过WindowManager.addView(View view, ViewGroup.LayoutParams params)可以看到：Window是一个抽象的概念，它以View的形式存在（不同于PhoneWindow，该Window是顶层View样式和行为的抽象类）,但同时Activity、Dialog、Toast等又必须通过Window与View建立关联。根View一一对应ViewRootImpl，WindowManager内部通过ViewRootImpl进行Window（即根View）的添加、删除、更新，而ViewRootImpl内部通过WindowSession和WindowManagerService通信，最终WindowManagerService完成根View的添加、删除、更新。

Android中的Activity、Dialog、Toast、PopupWindow、菜单、状态栏都是通过Window来实现对应的View的，视图都对应一个Window。