流程图
（大体流程，从Activity接受启动开始）
源码分析
基于API 23
Window创建
ActivityThread.handleLaunchActivity
ActivityThread.performLaunchActivity
ActivityThread处理并执行Activity启动
//ActivityThread
private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent) {
...
//获取WindowManagerService的Binder引用(proxy端)。
WindowManagerGlobal.initialize();
//执行Activity的onCreate,onStart,onResotreInstanceState方法
Activity a = performLaunchActivity(r, customIntent);
if (a != null) {
...
//执行Activity的onResume方法.
handleResumeActivity(r.token, false, r.isForward,
!r.activity.mFinished && !r.startsNotResumed, r.lastProcessedSeq, reason);
...
}
}
private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
//通过类加载器创建Activity
Activity activity = mInstrumentation.newActivity(cl, component.getClassName(), r.intent);
...
//通过LoadedApk的makeApplication方法来创建Application对象
Application app = r.packageInfo.makeApplication(false, mInstrumentation);
if (activity != null) {
...
// 执行 attach 方法
activity.attach(appContext, this, getInstrumentation(), r.token,
r.ident, app, r.intent, r.activityInfo, title, r.parent,
r.embeddedID, r.lastNonConfigurationInstances, config,
r.referrer, r.voiceInteractor, window);
...
//onCreate
mInstrumentation.callActivityOnCreate(activity, r.state);
//onStart
activity.performStart();
}
return activity;
}
Activity.attach
- 构造PhoneWindow （Window唯一具体实现）
- 设置自身为Window的Callback，从而Activity能作为callback接受window的key和touch事件
- 初始化且设置WindowManager，每个Activity对应一个WindowManager，通过WM与WMS进行通信
final void attach(...) {
//绑定上下文
attachBaseContext(context);
//创建Window,PhoneWindow是Window的唯一具体实现类
mWindow = new PhoneWindow(this, window);//此处的window==null，但不影响
mWindow.setWindowControllerCallback(this);
// 设置 Window.Callback
mWindow.setCallback(this);
...
//设置WindowManager
mWindow.setWindowManager(
(WindowManager)context.getSystemService(Context.WINDOW_SERVICE),
mToken, mComponent.flattenToString(),
(info.flags & ActivityInfo.FLAG_HARDWARE_ACCELERATED) != 0);
if (mParent != null) {
mWindow.setContainer(mParent.getWindow());
}
//创建完后通过getWindowManager就可以得到WindowManager实例
mWindowManager = mWindow.getWindowManager();//其实它是WindowManagerImpl
}
Window添加View过程
前面在handleLauncherActivity完成了PhoneWindow的创建过程，下面我们继续查看Activity执行生命周期handleResumeActivity方法，查看Activity对应View被加载到PhoneWindow容器过程
ActivityThread.handleResumeActivity
- 获取ActivityClientRecord，将对应DecorView设置为不可见，因为当前View还未绘制
- 通过Window对应的WindowManager执行addView（decor，l）操作
- View绘制完成后，会将decorView设置可见，展示该Activity对应内容，最后onResume完成
final void handleResumeActivity(IBinder token,
boolean clearHide, boolean isForward, boolean reallyResume, int seq, String reason) {
//把activity数据记录更新到ActivityClientRecord
ActivityClientRecord r = performResumeActivity(token, clearHide);
if (r != null) {
if (r.window == null && !a.mFinished && willBeVisible) {
r.window = r.activity.getWindow();
View decor = r.window.getDecorView();
decor.setVisibility(View.INVISIBLE);//不可见
ViewManager wm = a.getWindowManager();
WindowManager.LayoutParams l = r.window.getAttributes();
a.mDecor = decor;
l.type = WindowManager.LayoutParams.TYPE_BASE_APPLICATION;
...
if (a.mVisibleFromClient && !a.mWindowAdded) {
a.mWindowAdded = true;
wm.addView(decor, l);// 把decor添加到窗口上
}
}
//屏幕参数发生了改变
performConfigurationChanged(r.activity, r.tmpConfig);
WindowManager.LayoutParams l = r.window.getAttributes();
if (r.activity.mVisibleFromClient) {
ViewManager wm = a.getWindowManager();
View decor = r.window.getDecorView();
wm.updateViewLayout(decor, l);//更新窗口状态
}
...
if (r.activity.mVisibleFromClient) {
//已经成功添加到窗口上了（绘制和事件接收），设置为可见
r.activity.makeVisible();
}
//通知ActivityManagerService，Activity完成Resumed
ActivityManagerNative.getDefault().activityResumed(token);
}
}
WindowManagerImply.addView
WindowManagerGlobal.addView
- WindowManagerImpl的全局变量通过单例模式初始化了WindowManagerGlobal，（一个进程一个WMG对象）
- Window管理类添加View过程，创建ViewRootImpl，将View处理操作交给ViewRootImpl实现
// WindowManagerImply
public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
applyDefaultToken(params);
mGlobal.addView(view, params, mDisplay, mParentWindow);
}
// WindowManagerGlobal
public void addView(View view, ViewGroup.LayoutParams params,
Display display, Window parentWindow) {
synchronized (mLock) {
...
// 创建ViewRootImpl，并将View与之绑定
root = new ViewRootImpl(view.getContext(), display);
view.setLayoutParams(wparams);
mViews.add(view); // 将当前view添加到mView集合中
mRoots.add(root); // 将当前root添加mRoots集合中
mParams.add(wparams); // 将当前window的params添加到mParams集合中
}
// setView 完成View的绘制流程，并添加到window上
root.setView(view, wparams, panelParentView);
}
ViewRootImpl.setView
- ViewRootImpl构建过程中，会通过WindowManagerGlobal的getWindowSession（static方法）获取IWindowSession即WindowSession
- 执行requestLayout方法完成View的绘制流程
- 通过WindowSession与WindowManagerService通信，将View和InputChannel添加到WMS，从而展示View并可以接受输入事件
public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
...
int res
requestLayout();//执行 View的绘制流程
if ((mWindowAttributes.inputFeatures
& WindowManager.LayoutParams.INPUT_FEATURE_NO_INPUT_CHANNEL) == 0) {
// 创建InputChannel
mInputChannel = new InputChannel();
}
try {
//通过WindowSession进行IPC调用，将View添加到Window上
//mWindow即W类，用来接收WmS信息
//同时通过InputChannel接收触摸事件回调
res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
getHostVisibility(), mDisplay.getDisplayId(),
mAttachInfo.mContentInsets, mAttachInfo.mStableInsets,
mAttachInfo.mOutsets, mInputChannel);
}
...
//处理触摸事件回调
mInputEventReceiver = new WindowInputEventReceiver(mInputChannel,
Looper.myLooper());
}
WindowSession.addToDisplay
- Session执行addToDisplay方法，通过调用成员变量WMS进行addWindow操作
public int addToDisplay(...) {
return mService.addWindow(this, window, seq, attrs, viewVisibility, displayId,
outContentInsets, outStableInsets, outOutsets, outInputChannel);
}
WindowManagerService.addWindow
- 创建WindowState，保存Window状态
- 调整LayoutParams参数、设置input、设置window zOrder
- 执行WindowState的attach（创建Surface过程，详情见下一篇）
public int addWindow(Session session, IWindow client, int seq,
WindowManager.LayoutParams attrs, int viewVisibility, int displayId,
Rect outContentInsets, Rect outStableInsets, Rect outOutsets,InputChannel outInputChannel) {
... // 一堆check逻辑
WindowToken token = mTokenMap.get(attrs.token);
//创建 WindowState
WindowState win = new WindowState(this, session, client, token,
attachedWindow, appOp[0], seq, attrs, viewVisibility, displayContent);
...
//调整 WindowManager 的 LayoutParams 参数
mPolicy.adjustWindowParamsLw(win.mAttrs);
res = mPolicy.prepareAddWindowLw(win, attrs);
addWindowToListInOrderLocked(win, true);
// 设置 input
mInputManager.registerInputChannel(win.mInputChannel, win.mInputWindowHandle);
// 创建 Surface 与 SurfaceFlinger 通信，
win.attach();
mWindowMap.put(client.asBinder(), win);
if (win.canReceiveKeys()) {
//当该窗口能接收按键事件，则更新聚焦窗口
focusChanged = updateFocusedWindowLocked(UPDATE_FOCUS_WILL_ASSIGN_LAYERS,
false /*updateInputWindows*/);
}
assignLayersLocked(displayContent.getWindowList());
...
}
推荐阅读：图形系统总结
参考
Android Window 机制探索