Window的添加过程的WMS部分，将addWindow方法分为了3个部分来进行讲解，从addWindow方法我们得知WMS有3个重要的类分别是WindowToken、WindowState和DisplayContent
启动过程
1.1 WindowManagerService 的诞生
1.1.1 在 SystemServer 中的创建
WMS 是在 SystemServer 进程中启动的，SystemServer 进程是 Android 系统启动的时候初始化的，我们首先来看一下 SystemServer 的入口函数 main()
public final class SystemServer {
/**
* The main entry point from zygote.
*/
public static void main(String[] args) {
new SystemServer().run();
}
}
分析run方法
private void run() {
......
mSystemServiceManager = new SystemServiceManager(mSystemContext); // 代码 1
// Start services.
try {
traceBeginAndSlog("StartServices");
startBootstrapServices(); // 代码 2
startCoreServices(); // 代码 3
startOtherServices(); // 代码 4
SystemServerInitThreadPool.shutdown();
} catch (Throwable ex) {
Slog.e("System", "******************************************");
Slog.e("System", "************ Failure starting system services", ex);
throw ex;
} finally {
traceEnd();
}
}
代码1处，创建了一个 SystemServiceManager 对象
代码2处，调用 startBootstrapServices() 启动 ActivityManagerService、PackageManagerService 等服务进程
代码3处，调用 startCoreServices() 启动BatteryService、WebViewUpdateService 等服务进程
代码4处，调用 startOtherServices() 启动 WindowManagerService、InputManagerService 等服务进程
二. WMS 与 WindowManager 的通信
在上篇文章 初步理解 Window 体系 中，我们最后分析到了 ViewRootImpl，ViewRootImpl 是连接 WindowManager 和 WMS 的桥梁，自然他们之间的通信也是通过 ViewRootImpl 完成的。
2.1 ViewRootImpl 的成员变量
在 ViewRootImpl 中有两个个非常重要的成员变量：mWindowSession 和 mWindow，这两个变量都是用于 ViewRootImpl 和 WMS 通信使用的
public final class ViewRootImpl implements ViewParent,
View.AttachInfo.Callbacks, ThreadedRenderer.DrawCallbacks {
......
final IWindowSession mWindowSession;
final W mWindow;
......
public ViewRootImpl(Context context, Display display) {
mContext = context;
// 代码 1，通过 WindowManagerGlobal.getWindowSession() 方法得到一个 IWindowSession 对象
mWindowSession = WindowManagerGlobal.getWindowSession();
......
// 代码 2，通过 W 构造方法直接创建一个新的 W 对象
mWindow = new W(this);
......
}
......
}
2.1.1 IWindowSession
IWindowSession 是一个 AIDL 接口，其服务端进程是 WMS，客户端进程是应用进程，IWindowSession 的创建是在 WindowManagerGlobal 中，如下所示：
public final class WindowManagerGlobal {
private static IWindowManager sWindowManagerService;
private static IWindowSession sWindowSession;
......
public static IWindowManager getWindowManagerService() {
synchronized (WindowManagerGlobal.class) {
if (sWindowManagerService == null) {
sWindowManagerService = IWindowManager.Stub.asInterface(
ServiceManager.getService("window"));
try {
if (sWindowManagerService != null) {
ValueAnimator.setDurationScale(
sWindowManagerService.getCurrentAnimatorScale());
}
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}
return sWindowManagerService;
}
}
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;
}
}
......
}
从 getWindowSession() 方法中我们可以看出，IWindowSession 对象的创建依赖于 IWindowManager 对象
IWindowManager 也是一个 AIDL 接口，通过 getWindowManagerService() 方法得到其对象，在 getWindowManagerService() 方法中，可以看到是典型的 Android 中 Binder 通信得到服务端在客户端进程中的代理对象的方式，远程端的对象即是 WMS，WMS 实现了 IWindowManager 接口
public class WindowManagerService extends IWindowManager.Stub
implements Watchdog.Monitor, WindowManagerPolicy.WindowManagerFuncs {
......
}
在 getWindowSession() 方法中，我们可以看到是调用了 IWindowManager 的 openSession 方法，其实际的实现是在 WMS 中，WMS 中的 openSession 方法如下所示
public class WindowManagerService extends IWindowManager.Stub
implements Watchdog.Monitor, WindowManagerPolicy.WindowManagerFuncs {
@Override
public IWindowSession openSession(IWindowSessionCallback callback, IInputMethodClient client,
IInputContext inputContext) {
if (client == null) throw new IllegalArgumentException("null client");
if (inputContext == null) throw new IllegalArgumentException("null inputContext");
Session session = new Session(this, callback, client, inputContext);
return session;
}
}
可以看到，其实 ViewRootImpl 中的 IWindowSession 对象实际对应着 WMS 中的 Session 对象。
WindowManagerGlobal 和 WMS 实现的是单方向的通信，都是通过如下图所示的 Binder 方式进行进程间通信的
WindowManagerGlobal.png
2.1.2 W
W 类是 ViewRootImpl 的一个内部类，实现了 IWindow 接口，IWindow 也是一个 AIDL 接口，可以猜想到，IWindow 接口是供 WMS 使用的，WSM 通过调用 IWindow 一些方法，通过 Binder 通信的方式，最后执行到了 W 中对应的方法中
public final class ViewRootImpl implements ViewParent,
View.AttachInfo.Callbacks, ThreadedRenderer.DrawCallbacks {
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;
}
@Override
public void resized(Rect frame, Rect overscanInsets, Rect contentInsets,
Rect visibleInsets, Rect stableInsets, Rect outsets, boolean reportDraw,
MergedConfiguration mergedConfiguration, Rect backDropFrame, boolean forceLayout,
boolean alwaysConsumeNavBar, int displayId) {
final ViewRootImpl viewAncestor = mViewAncestor.get();
if (viewAncestor != null) {
viewAncestor.dispatchResized(frame, overscanInsets, contentInsets,
visibleInsets, stableInsets, outsets, reportDraw, mergedConfiguration,
backDropFrame, forceLayout, alwaysConsumeNavBar, displayId);
}
}
@Override
public void moved(int newX, int newY) {
final ViewRootImpl viewAncestor = mViewAncestor.get();
if (viewAncestor != null) {
viewAncestor.dispatchMoved(newX, newY);
}
}
@Override
public void dispatchAppVisibility(boolean visible) {
final ViewRootImpl viewAncestor = mViewAncestor.get();
if (viewAncestor != null) {
viewAncestor.dispatchAppVisibility(visible);
}
}
@Override
public void dispatchGetNewSurface() {
final ViewRootImpl viewAncestor = mViewAncestor.get();
if (viewAncestor != null) {
viewAncestor.dispatchGetNewSurface();
}
}
@Override
public void windowFocusChanged(boolean hasFocus, boolean inTouchMode) {
final ViewRootImpl viewAncestor = mViewAncestor.get();
if (viewAncestor != null) {
viewAncestor.windowFocusChanged(hasFocus, inTouchMode);
}
}
private static int checkCallingPermission(String permission) {
try {
return ActivityManager.getService().checkPermission(
permission, Binder.getCallingPid(), Binder.getCallingUid());
} catch (RemoteException e) {
return PackageManager.PERMISSION_DENIED;
}
}
......
}
}
比如在 ViewRootImpl#setView 方法中，有如下代码，在代码 1 处通过 mWindowSession 调用 addToDisplay 方法时，会将 mWindow 传入，最后传给 WMS，这样 WMS 便得到了一个 W 对象的实例对象。
public final class ViewRootImpl implements ViewParent,
View.AttachInfo.Callbacks, ThreadedRenderer.DrawCallbacks {
public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
synchronized (this) {
if (mView == null) {
......
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();
if ((mWindowAttributes.inputFeatures
& WindowManager.LayoutParams.INPUT_FEATURE_NO_INPUT_CHANNEL) == 0) {
mInputChannel = new InputChannel();
}
mForceDecorViewVisibility = (mWindowAttributes.privateFlags
& PRIVATE_FLAG_FORCE_DECOR_VIEW_VISIBILITY) != 0;
try {
mOrigWindowType = mWindowAttributes.type;
mAttachInfo.mRecomputeGlobalAttributes = true;
collectViewAttributes();
// 代码 1
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();
}
}
......
}
}
}
}
从上面代码可以看到，在 ViewRootImpl 中不仅实现了从 ViewRootImpl 向 WMS 的通信，也实现了从 WMS 向 ViewRootImpl 的通信，如下图所示
image.png
网友评论