Android之Window与WindowManager

基本概念

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

{
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

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

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

创建窗口：构造函数中

初始化DecorView并将Dialog的View添加到DecorView中：setContentView（）

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

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。

WindowManager.addView()：调用2

WindowManagerGlobal.addView():

创建ViewRootImpl

调用3

ViewRootImpl.setView()：

requestLayout()

mWindowSession.addToDisplay

总结

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。