四、Activity的显示
从AMS的startActivity开始经过相当复杂的调用，终于调用到ApplicationThread中，通过跨进程的方式调用了scheduleLaunchActivity，然后扔到H这个handler中进行处理了，然后再主线程中调用handleLaunchActivity方法。核心的方法有2个，一个是performLaunchActivity，另一个是handleResumeActivity。
private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent, String reason) {
...
Activity a = performLaunchActivity(r, customIntent);
if (a != null) {
r.createdConfig = new Configuration(mConfiguration);
reportSizeConfigurations(r);
Bundle oldState = r.state;
handleResumeActivity(r.token, false, r.isForward,
!r.activity.mFinished && !r.startsNotResumed, r.lastProcessedSeq, reason);
...
} else {
// If there was an error, for any reason, tell the activity manager to stop us.
try {
ActivityManagerNative.getDefault()
.finishActivity(r.token, Activity.RESULT_CANCELED, null,
Activity.DONT_FINISH_TASK_WITH_ACTIVITY);
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
}
}
这2个方法就涉及到了初始化和显示了。在Activity的启动流程中都有，这里也只介绍核心的部分，首先是performLaunchActivity。
private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
...
Activity activity = null;
try {
java.lang.ClassLoader cl = r.packageInfo.getClassLoader();
activity = mInstrumentation.newActivity(
cl, component.getClassName(), r.intent);//反射方式，初始Activity实例
...
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);//这里初始化和窗口相关的
....
return activity;
}
只看2个，一个是Instrumentation通过反射方式初始化Activity，核心的地方在第二个，也即是Activity的attach方法。
final void attach(Context context, ActivityThread aThread,
Instrumentation instr, IBinder token, int ident,
Application application, Intent intent, ActivityInfo info,
CharSequence title, Activity parent, String id,
NonConfigurationInstances lastNonConfigurationInstances,
Configuration config, String referrer, IVoiceInteractor voiceInteractor,
Window window) {
...
mWindow = new PhoneWindow(this, window);
mWindow.setWindowControllerCallback(this);
mWindow.setCallback(this);
mWindow.setOnWindowDismissedCallback(this);
mWindow.getLayoutInflater().setPrivateFactory(this);
....
mWindow.setWindowManager(
(WindowManager)context.getSystemService(Context.WINDOW_SERVICE),
mToken, mComponent.flattenToString(),
(info.flags & ActivityInfo.FLAG_HARDWARE_ACCELERATED) != 0);
...
}
这里初始化了PhoneWindow，再来看看handleResumeActivity，这里是Activity显示的核心代码
final void handleResumeActivity(IBinder token,
boolean clearHide, boolean isForward, boolean reallyResume, int seq, String reason) {
...
r = performResumeActivity(token, clearHide, reason);//这里会调用Activity的onResume方法
if (r != null) {
...
if (r.window == null && !a.mFinished && willBeVisible) {
r.window = r.activity.getWindow();
View decor = r.window.getDecorView();//这里初始化DecorView
decor.setVisibility(View.INVISIBLE);
ViewManager wm = a.getWindowManager();
WindowManager.LayoutParams l = r.window.getAttributes();
a.mDecor = decor;
l.type = WindowManager.LayoutParams.TYPE_BASE_APPLICATION;
l.softInputMode |= forwardBit;
if (r.mPreserveWindow) {
a.mWindowAdded = true;
r.mPreserveWindow = false;
// Normally the ViewRoot sets up callbacks with the Activity
// in addView->ViewRootImpl#setView. If we are instead reusing
// the decor view we have to notify the view root that the
// callbacks may have changed.
ViewRootImpl impl = decor.getViewRootImpl();
if (impl != null) {
impl.notifyChildRebuilt();
}
}
if (a.mVisibleFromClient && !a.mWindowAdded) {
a.mWindowAdded = true;
wm.addView(decor, l);//这里是核心部分，初始化ViewRootImpl
}
...
WindowManager.LayoutParams l = r.window.getAttributes();
if ((l.softInputMode
& WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION)
!= forwardBit) {
l.softInputMode = (l.softInputMode
& (~WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION))
| forwardBit;
if (r.activity.mVisibleFromClient) {
ViewManager wm = a.getWindowManager();
View decor = r.window.getDecorView();
wm.updateViewLayout(decor, l);//这里开始了绘制三部曲
}
}
r.activity.mVisibleFromServer = true;
mNumVisibleActivities++;
if (r.activity.mVisibleFromClient) {
r.activity.makeVisible();
}
}
...
}
}
上述代码中，performResumeActivity会调用onResume，而r.window.getDecorView()则会初始化DecorView,DecorView是视图的根节点。其中一个非常重要的调用是wm.addView(decor, l),wm是WindowManagerImpl，来看看这一块的调用
@Override
public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
applyDefaultToken(params);
mGlobal.addView(view, params, mContext.getDisplay(), mParentWindow);
}
public void addView(View view, ViewGroup.LayoutParams params,
Display display, Window parentWindow) {
....
root = new ViewRootImpl(view.getContext(), display);
view.setLayoutParams(wparams);
mViews.add(view);
mRoots.add(root);
mParams.add(wparams);
}
// do this last because it fires off messages to start doing things
try {
root.setView(view, wparams, panelParentView);//这里比较重要的地方在于通过管道方式实现事件分发
} catch (RuntimeException e) {
...
}
}
上述代码主要是初始化ViewRootImpl，ViewRootImpl有2个成员变量需要注意的，一个是mSurface，一个是mWindowSession，其中mSurface是直接就初始化的，此时的mSurface成员变量没有什么意义，mWindowSession是在构造方法中初始化。
public ViewRootImpl(Context context, Display display) {
mContext = context;
mWindowSession = WindowManagerGlobal.getWindowSession();
...
}
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;
}
}
通过跨进程调用到WMS的openSession方法，返回了Session的引用。
@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;
}
ViewRootImpl的setView方法
public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
synchronized (this) {
...
try {
mOrigWindowType = mWindowAttributes.type;
mAttachInfo.mRecomputeGlobalAttributes = true;
collectViewAttributes();
res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
getHostVisibility(), mDisplay.getDisplayId(),
mAttachInfo.mContentInsets, mAttachInfo.mStableInsets,
mAttachInfo.mOutsets, mInputChannel);//通过管道，实现全双工方式的事件分发
}
...
}
}
再来看wm.updateViewLayout(decor, l)，这里是真正开始调用绘制的地方
@Override
public void updateViewLayout(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
applyDefaultToken(params);
mGlobal.updateViewLayout(view, params);
}
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);
root.setLayoutParams(wparams, false);//这里的root是ViewRootImpl
}
}
调用到了ViewRootImpl的setLayoutParams方法
void setLayoutParams(WindowManager.LayoutParams attrs, boolean newView) {
synchronized (this) {
...
if (newView) {
mSoftInputMode = attrs.softInputMode;
requestLayout();
}
...
mWindowAttributesChanged = true;
scheduleTraversals();
}
}
requestLayout也是调用的scheduleTraversals接口，看看这一块的代码
void scheduleTraversals() {
if (!mTraversalScheduled) {
mTraversalScheduled = true;
mTraversalBarrier = mHandler.getLooper().getQueue().postSyncBarrier();
mChoreographer.postCallback(
Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);
if (!mUnbufferedInputDispatch) {
scheduleConsumeBatchedInput();
}
notifyRendererOfFramePending();
pokeDrawLockIfNeeded();
}
}
上面会把mTraversalRunnable加入到mChoreographer中，当Choreographer调用doFrame的时候，调用mTraversalRunnable的run方法，接着就调用了performTraversals方法。这个方法非常长
private void performTraversals() {
....
relayoutResult = relayoutWindow(params, viewVisibility, insetsPending);//主要分析这里
...
if (!mStopped || mReportNextDraw) {
boolean focusChangedDueToTouchMode = ensureTouchModeLocally(
(relayoutResult&WindowManagerGlobal.RELAYOUT_RES_IN_TOUCH_MODE) != 0);
if (focusChangedDueToTouchMode || mWidth != host.getMeasuredWidth()
|| mHeight != host.getMeasuredHeight() || contentInsetsChanged ||
updatedConfiguration) {
int childWidthMeasureSpec = getRootMeasureSpec(mWidth, lp.width);
int childHeightMeasureSpec = getRootMeasureSpec(mHeight, lp.height);
if (DEBUG_LAYOUT) Log.v(mTag, "Ooops, something changed! mWidth="
+ mWidth + " measuredWidth=" + host.getMeasuredWidth()
+ " mHeight=" + mHeight
+ " measuredHeight=" + host.getMeasuredHeight()
+ " coveredInsetsChanged=" + contentInsetsChanged);
// Ask host how big it wants to be
performMeasure(childWidthMeasureSpec, childHeightMeasureSpec);//绘制流程第一步
...
if (measureAgain) {
if (DEBUG_LAYOUT) Log.v(mTag,
"And hey let's measure once more: width=" + width
+ " height=" + height);
performMeasure(childWidthMeasureSpec, childHeightMeasureSpec);
}
layoutRequested = true;
}
}
} else {
// Not the first pass and no window/insets/visibility change but the window
// may have moved and we need check that and if so to update the left and right
// in the attach info. We translate only the window frame since on window move
// the window manager tells us only for the new frame but the insets are the
// same and we do not want to translate them more than once.
maybeHandleWindowMove(frame);
}
final boolean didLayout = layoutRequested && (!mStopped || mReportNextDraw);
boolean triggerGlobalLayoutListener = didLayout
|| mAttachInfo.mRecomputeGlobalAttributes;
if (didLayout) {
performLayout(lp, mWidth, mHeight);//绘制流程第二步
...
boolean cancelDraw = mAttachInfo.mTreeObserver.dispatchOnPreDraw() || !isViewVisible;
if (!cancelDraw && !newSurface) {
if (mPendingTransitions != null && mPendingTransitions.size() > 0) {
for (int i = 0; i < mPendingTransitions.size(); ++i) {
mPendingTransitions.get(i).startChangingAnimations();
}
mPendingTransitions.clear();
}
performDraw();//绘制流程第三步
} else {
if (isViewVisible) {
// Try again
scheduleTraversals();
} else if (mPendingTransitions != null && mPendingTransitions.size() > 0) {
for (int i = 0; i < mPendingTransitions.size(); ++i) {
mPendingTransitions.get(i).endChangingAnimations();
}
mPendingTransitions.clear();
}
}
mIsInTraversal = false;
}
在开始绘制流程三部曲之前，先调用了relayoutWindow，
private int relayoutWindow(WindowManager.LayoutParams params, int viewVisibility,
boolean insetsPending) throws RemoteException {
...
int relayoutResult = mWindowSession.relayout(
mWindow, mSeq, params,
(int) (mView.getMeasuredWidth() * appScale + 0.5f),
(int) (mView.getMeasuredHeight() * appScale + 0.5f),
viewVisibility, insetsPending ? WindowManagerGlobal.RELAYOUT_INSETS_PENDING : 0,
mWinFrame, mPendingOverscanInsets, mPendingContentInsets, mPendingVisibleInsets,
mPendingStableInsets, mPendingOutsets, mPendingBackDropFrame, mPendingConfiguration,
mSurface);//这里才是真正让mSurface起作用的地方
...
}
上面mWindowSession.relayout，会调用到WMS的relayoutWindow方法中，
public int relayoutWindow(Session session, IWindow client, int seq,
WindowManager.LayoutParams attrs, int requestedWidth,
int requestedHeight, int viewVisibility, int flags,
Rect outFrame, Rect outOverscanInsets, Rect outContentInsets,
Rect outVisibleInsets, Rect outStableInsets, Rect outOutsets, Rect outBackdropFrame,
Configuration outConfig, Surface outSurface) {
...
if (viewVisibility == View.VISIBLE &&
(win.mAppToken == null || !win.mAppToken.clientHidden)) {
...
try {
result = createSurfaceControl(outSurface, result, win, winAnimator);//这里会将真正surface指向的FrameBuffer赋值给outSurface
} catch (Exception e) {
...
}
....
return result;
}
WMS向SurfaceFlinger申请一块FrameBuffer，然后通过远程调用，将指向这个FrameBuffer的指针赋值给ViewRootImpl的Surface，于是就可以通过Surface的canvas对这一块的数据区域进行各种操作了。也就是绘制三部曲中的第三步的performDraw中的canvas。后面的三步在附录的Activity启动流程(2)中有说明，不做介绍。
五、事件如何分发到Activity中
linux层通过EventHub读取输入事件，WMS通过InputManager提供的接口，开启一个线程不断的从EventHub中读取事件，然后通过InputDispatcher分发到客户端ViewRootImpl的WindowInputEventReceiver中来处理。刚才代码中调用ViewRootImpl调用setView方法会调用
mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
getHostVisibility(), mDisplay.getDisplayId(),
mAttachInfo.mContentInsets, mAttachInfo.mStableInsets,
mAttachInfo.mOutsets, mInputChannel);//通过管道，实现全双工方式的事件分发
它会调用到WMS的addWindow方法
public int addWindow(Session session, IWindow client, int seq,
WindowManager.LayoutParams attrs, int viewVisibility, int displayId,
Rect outContentInsets, Rect outStableInsets, Rect outOutsets,
InputChannel outInputChannel) {
...
WindowState win = new WindowState(this, session, client, token,
attachedWindow, appOp[0], seq, attrs, viewVisibility, displayContent);
...
final boolean openInputChannels = (outInputChannel != null
&& (attrs.inputFeatures & INPUT_FEATURE_NO_INPUT_CHANNEL) == 0);
if (openInputChannels) {
win.openInputChannel(outInputChannel);
}
...
return res;
}
然后调用了WindowState的openInputChannel方法，把它注册到InputManager中
void openInputChannel(InputChannel outInputChannel) {
if (mInputChannel != null) {
throw new IllegalStateException("Window already has an input channel.");
}
String name = makeInputChannelName();
InputChannel[] inputChannels = InputChannel.openInputChannelPair(name);//全双工方式
mInputChannel = inputChannels[0];
mClientChannel = inputChannels[1];
mInputWindowHandle.inputChannel = inputChannels[0];
if (outInputChannel != null) {
mClientChannel.transferTo(outInputChannel);
mClientChannel.dispose();
mClientChannel = null;
} else {
// If the window died visible, we setup a dummy input channel, so that taps
// can still detected by input monitor channel, and we can relaunch the app.
// Create dummy event receiver that simply reports all events as handled.
mDeadWindowEventReceiver = new DeadWindowEventReceiver(mClientChannel);
}
mService.mInputManager.registerInputChannel(mInputChannel, mInputWindowHandle);//注册到InputManager中
}
然后当有事件时，通过管道跨进程发送给ViewRootImpl的WindowInputEventReceiver，然后调用onInputEvent->enqueueInputEvent->doProcessInputEvents->deliverInputEvent->ViewPostImeInputStage.deliver->ViewPostImeInputStage.apply->ViewPostImeInputStage.onProcess。根据不同事件类型，分别对应不同的处理。
protected int onProcess(QueuedInputEvent q) {
if (q.mEvent instanceof KeyEvent) {
return processKeyEvent(q);
} else {
final int source = q.mEvent.getSource();
if ((source & InputDevice.SOURCE_CLASS_POINTER) != 0) {
return processPointerEvent(q);
} else if ((source & InputDevice.SOURCE_CLASS_TRACKBALL) != 0) {
return processTrackballEvent(q);
} else {
return processGenericMotionEvent(q);
}
}
}
这里的事件分发可以看附录里面的Android Touch事件解析，后面的从dispatchTouchEvent开始的，附录的Activity的启动流程(3)中有详细介绍，不做分析。
附录：
：首先介绍了进程的启动流程中nativeZygoteInit后面的流程
Activity的启动流程(1)：
http://blog.youkuaiyun.com/newhope1106/article/details/53355189
：介绍了Activity在java层的启动流程
Activity的启动流程(2)：
http://blog.youkuaiyun.com/newhope1106/article/details/53363062
：介绍了Activity的绘制流程
Activity的启动流程(3)：
http://blog.youkuaiyun.com/newhope1106/article/details/53363208
：介绍了Activity的事件分发流程
：介绍了内核层binder驱动和native层的service manager的初始化
：介绍了AMS的注册过程
：介绍了Activity的启动的接口调用过程
android进程的启动流程(基于android6.0)：
http://blog.youkuaiyun.com/newhope1106/article/details/54932800
：介绍了进程的创建流程
Android Touch事件解析：
http://blog.youkuaiyun.com/xuezhe__/article/details/50977747
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