代碼基於Android 28（9.0、pie）分析
一、引子
在Activity啓動流程分析一文中，分析了從startActivity()到Activity對象創建的過程，之後分析下Activity對象創建到顯示到屏幕的過程。
二、Activity對象創建到顯示到屏幕
2.1 activity.attach()
這裏從上部分最後的activity.attach()方法講起
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, ActivityConfigCallback activityConfigCallback) {
attachBaseContext(context);
mFragments.attachHost(null /*parent*/);
mWindow = new PhoneWindow(this, window, activityConfigCallback);
mWindow.setWindowControllerCallback(this);
mWindow.setCallback(this);
mWindow.setOnWindowDismissedCallback(this);
mWindow.getLayoutInflater().setPrivateFactory(this);
if (info.softInputMode != WindowManager.LayoutParams.SOFT_INPUT_STATE_UNSPECIFIED) {
mWindow.setSoftInputMode(info.softInputMode);
}
if (info.uiOptions != 0) {
mWindow.setUiOptions(info.uiOptions);
}
mUiThread = Thread.currentThread();
mMainThread = aThread;
mInstrumentation = instr;
...
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());
}
mWindowManager = mWindow.getWindowManager();
mCurrentConfig = config;
mWindow.setColorMode(info.colorMode);
...
}
這裏將Activity中的Window類型變量mWindow初始化爲PhoneWindow，並通過Window的setCallback(Window.Callback)將Activity與PhoneWindow綁定。其中Window.Callback接口包含了一些開發中常用方法，比如dispatchTouchEvent(MotionEvent event)、onWindowFocusChanged(boolean hasFocus)、onAttachedToWindow()、nDetachedFromWindow()等。之後通過Window.setWindowManager()方法初始化了Window中的mWindowManger變量，是WindowMangerImpl類型的對象，最後將該對象從Window中取出，設置給Activity的mWindowManager變量。Window、Activity可以通過它們調用WindowManager服務的方法。需要注意的是WindowManager雖然是通過Context.getSystemService()獲取的變量，但並不是WindowManager服務的IBinder對象。這可以從SystemServiceRegistry中看到
registerService(Context.WINDOW_SERVICE, WindowManager.class,
new CachedServiceFetcher<WindowManager>() {
@Override
public WindowManager createService(ContextImpl ctx) {
return new WindowManagerImpl(ctx);
}});
與之對比的比如WifiManager
registerService(Context.WIFI_SERVICE, WifiManager.class,
new CachedServiceFetcher<WifiManager>() {
@Override
public WifiManager createService(ContextImpl ctx) throws ServiceNotFoundException {
IBinder b = ServiceManager.getServiceOrThrow(Context.WIFI_SERVICE);
IWifiManager service = IWifiManager.Stub.asInterface(b);
return new WifiManager(ctx.getOuterContext(), service,
ConnectivityThread.getInstanceLooper());
}});
2.2 setContentView()
當我們調用Activity的setContentView()方法給Activity設置顯示內容時，實質上調用了
PhoneWindow的相應方法，比如Activity的setContentView(int layoutResId)方法
public void setContentView(@LayoutRes int layoutResID) {
getWindow().setContentView(layoutResID);
initWindowDecorActionBar();
}
public Window getWindow() {
return mWindow;
}
看下，PhoneWindow的setContentView(int layoutResId)方法
@Override
public void setContentView(int layoutResID) {
if (mContentParent == null) {
installDecor();
} else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
mContentParent.removeAllViews();
}
if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
final Scene newScene = Scene.getSceneForLayout(mContentParent, layoutResID,
getContext());
transitionTo(newScene);
} else {
mLayoutInflater.inflate(layoutResID, mContentParent);
}
...
}
PhoneWindow中有個DecorView類型的mDecor變量，installDecor()方法中對其初始化。
private void installDecor() {
if (mDecor == null) {
mDecor = generateDecor(-1);
...
} else {
mDecor.setWindow(this);
}
if (mContentParent == null) {
mContentParent = generateLayout(mDecor);
}
...
}
其中，generateDecor()中通過DecorView的構造方法創建了DecorView的對象。
protected DecorView generateDecor(int featureId) {
Context context;
if (mUseDecorContext) {
Context applicationContext = getContext().getApplicationContext();
if (applicationContext == null) {
context = getContext();
} else {
context = new DecorContext(applicationContext, getContext());
if (mTheme != -1) {
context.setTheme(mTheme);
}
}
} else {
context = getContext();
}
return new DecorView(context, featureId, this, getAttributes());
}
可以看到，DecorView的構造方法，傳入了Window的引用，DecorView會將其保存到內部的mWindow變量上。
DecorView添加子佈局並不在構造方法中，而是在對mContentParent進行初始化的generateLayout(DecorView)方法中。
protected ViewGroup generateLayout(DecorView decor) {
...
mDecor.startChanging();
mDecor.onResourcesLoaded(mLayoutInflater, layoutResource);
ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
...
mDecor.finishChanging();
return contentParent;
}
其中，DecorVIew的onResourcesLoaded()方法真正對其添加子View操作。
void onResourcesLoaded(LayoutInflater inflater, int layoutResource) {
...
mDecorCaptionView = createDecorCaptionView(inflater);
final View root = inflater.inflate(layoutResource, null);
if (mDecorCaptionView != null) {
if (mDecorCaptionView.getParent() == null) {
addView(mDecorCaptionView,
new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
}
mDecorCaptionView.addView(root,
new ViewGroup.MarginLayoutParams(MATCH_PARENT, MATCH_PARENT));
} else {
// Put it below the color views.
addView(root, 0, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
}
mContentRoot = (ViewGroup) root;
initializeElevation();
}
2.3 界面顯示
經過attach()，Activity和PhoneWindow、WindowManager建立起聯繫；
經過setContentView()，PhoneWindow與DecorView、ContentParent、ContentView建立起聯繫。
但這並不會將界面顯示到屏幕上，那是誰在哪裏通知WindowManager服務顯示界面的呢？又是在什麼時候呢？
由於Activity是在首次onResume()回調後顯示頁面，所以去ActivityThread的handleResumeActivity(IBinder token, boolean finalStateRequest, boolean isForward,
String reason)方法中看看，
@Override
public void handleResumeActivity(IBinder token, boolean finalStateRequest, boolean isForward, String reason) {
...
final ActivityClientRecord r = performResumeActivity(token, finalStateRequest, reason);
if (r == null) {
// We didn't actually resume the activity, so skipping any follow-up actions.
return;
}
final Activity a = r.activity;
...
// If the window hasn't yet been added to the window manager,
// and this guy didn't finish itself or start another activity,
// then go ahead and add the window.
boolean willBeVisible = !a.mStartedActivity;
if (!willBeVisible) {
try {
willBeVisible = ActivityManager.getService().willActivityBeVisible(
a.getActivityToken());
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}
if (r.window == null && !a.mFinished && willBeVisible) {
r.window = r.activity.getWindow();
View decor = r.window.getDecorView();
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 (a.mVisibleFromClient) {
if (!a.mWindowAdded) {
a.mWindowAdded = true;
wm.addView(decor, l);
} else {
a.onWindowAttributesChanged(l);
}
}
// If the window has already been added, but during resume
// we started another activity, then don't yet make the
// window visible.
} else if (!willBeVisible) {
r.hideForNow = true;
}
// The window is now visible if it has been added, we are not
// simply finishing, and we are not starting another activity.
if (!r.activity.mFinished && willBeVisible && r.activity.mDecor != null && !r.hideForNow) {
if (r.newConfig != null) {
performConfigurationChangedForActivity(r, r.newConfig);
r.newConfig = null;
}
...
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);
}
}
r.activity.mVisibleFromServer = true;
mNumVisibleActivities++;
if (r.activity.mVisibleFromClient) {
r.activity.makeVisible(); // 會調用mDecor.setVisibility(View.VISIBLE);
}
}
...
}
關注下wm.addView(decor, l); 跨進程（WindowManager服務進程）調用了WindowMangerImpl的addView方法
@Override
public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
applyDefaultToken(params);
mGlobal.addView(view, params, mContext.getDisplay(), mParentWindow);
}
其實調用了WindowManagerGlobal類的addView()方法
public void addView(View view, ViewGroup.LayoutParams params,
Display display, Window parentWindow) {
...
final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams) params;
....
ViewRootImpl root;
View panelParentView = null;
synchronized (mLock) {
...
int index = findViewLocked(view, false);
if (index >= 0) {
if (mDyingViews.contains(view)) {
// Don't wait for MSG_DIE to make it's way through root's queue.
mRoots.get(index).doDie();
} else {
throw new IllegalStateException("View " + view
+ " has already been added to the window manager.");
}
// The previous removeView() had not completed executing. Now it has.
}
...
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);
} catch (RuntimeException e) {
// BadTokenException or InvalidDisplayException, clean up.
if (index >= 0) {
removeViewLocked(index, true);
}
throw e;
}
}
}
重點關注下root.setView()方法，調用了ViewRootImpl的setView()方法。
public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
synchronized (this) {
if (mView == null) {
mView = view;
...
try {
mOrigWindowType = mWindowAttributes.type;
mAttachInfo.mRecomputeGlobalAttributes = true;
collectViewAttributes();
res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
getHostVisibility(), mDisplay.getDisplayId(), mWinFrame,
mAttachInfo.mContentInsets, mAttachInfo.mStableInsets,
mAttachInfo.mOutsets, mAttachInfo.mDisplayCutout, 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();
}
}
...
if (DEBUG_LAYOUT) Log.v(mTag, "Added window " + mWindow);
if (res < WindowManagerGlobal.ADD_OKAY) {
mAttachInfo.mRootView = null;
mAdded = false;
mFallbackEventHandler.setView(null);
unscheduleTraversals();
setAccessibilityFocus(null, null);
switch (res) {
case WindowManagerGlobal.ADD_BAD_APP_TOKEN:
case WindowManagerGlobal.ADD_BAD_SUBWINDOW_TOKEN:
throw new WindowManager.BadTokenException(
"Unable to add window -- token " + attrs.token
+ " is not valid; is your activity running?");
case WindowManagerGlobal.ADD_NOT_APP_TOKEN:
throw new WindowManager.BadTokenException(
"Unable to add window -- token " + attrs.token
+ " is not for an application");
case WindowManagerGlobal.ADD_APP_EXITING:
throw new WindowManager.BadTokenException(
"Unable to add window -- app for token " + attrs.token
+ " is exiting");
case WindowManagerGlobal.ADD_DUPLICATE_ADD:
throw new WindowManager.BadTokenException(
"Unable to add window -- window " + mWindow
+ " has already been added");
case WindowManagerGlobal.ADD_STARTING_NOT_NEEDED:
// Silently ignore -- we would have just removed it
// right away, anyway.
return;
case WindowManagerGlobal.ADD_MULTIPLE_SINGLETON:
throw new WindowManager.BadTokenException("Unable to add window "
+ mWindow + " -- another window of type "
+ mWindowAttributes.type + " already exists");
case WindowManagerGlobal.ADD_PERMISSION_DENIED:
throw new WindowManager.BadTokenException("Unable to add window "
+ mWindow + " -- permission denied for window type "
+ mWindowAttributes.type);
case WindowManagerGlobal.ADD_INVALID_DISPLAY:
throw new WindowManager.InvalidDisplayException("Unable to add window "
+ mWindow + " -- the specified display can not be found");
case WindowManagerGlobal.ADD_INVALID_TYPE:
throw new WindowManager.InvalidDisplayException("Unable to add window "
+ mWindow + " -- the specified window type "
+ mWindowAttributes.type + " is not valid");
}
throw new RuntimeException(
"Unable to add window -- unknown error code " + res);
}
...
}
}
}
這個方法主要做了兩件事，第一件事是調用了mWindowSession的addToDisplay()方法，
res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
getHostVisibility(), mDisplay.getDisplayId(), mWinFrame, mAttachInfo.mContentInsets, mAttachInfo.mStableInsets, mAttachInfo.mOutsets, mAttachInfo.mDisplayCutout, mInputChannel);
第二件事是處理上面方法的返回值，對異常情況進行處理。主要關注第一件事。
首先mWindowSession是IWindowSession類型的變量，它被初始化爲
public ViewRootImpl(Context context, Display display) {
mContext = context;
mWindowSession = WindowManagerGlobal.getWindowSession();
...
}
看下WindowManagerGlobal的getWindowSession()方法。
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;
}
}
public static IWindowManager getWindowManagerService() {
synchronized (WindowManagerGlobal.class) {
if (sWindowManagerService == null) {
sWindowManagerService = IWindowManager.Stub.asInterface(
ServiceManager.getService("window"));
...
}
return sWindowManagerService;
}
}
可以看到終於找到了Window服務，直接找WindowManagerService的openSession()方法，注意這是個ipc調用。
@Override
public IWindowSession openSession(IWindowSessionCallback callback, IInputMethodClient client,
IInputContext inputContext) {
...
Session session = new Session(this, callback, client, inputContext);
return session;
}
返回的是Session對象，看下它的addToDisplay()方法。
@Override
public int addToDisplay(IWindow window, int seq, WindowManager.LayoutParams attrs,
int viewVisibility, int displayId, Rect outFrame, Rect outContentInsets,
Rect outStableInsets, Rect outOutsets,
DisplayCutout.ParcelableWrapper outDisplayCutout, InputChannel outInputChannel) {
return mService.addWindow(this, window, seq, attrs, viewVisibility, displayId, outFrame,
outContentInsets, outStableInsets, outOutsets, outDisplayCutout, outInputChannel);
}
跨進程調用了WindowMangerService類的addWindow()方法，這個方法實現了Window的添加。
2.4 界面刷新
ViewRootImpl中
scheduleTraversals()
mChoreographer.postCallback(
Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);
->TraversalRunnable
final class TraversalRunnable implements Runnable {
@Override
public void run() {
doTraversal();
}
}
final TraversalRunnable mTraversalRunnable = new TraversalRunnable();
doTraversal()->
performTraversals()->
performDraw()->
draw(boolean fullRedrawNeeded)->
drawSoftware(Surface surface, AttachInfo attachInfo, int xoff, int yoff,
boolean scalingRequired, Rect dirty, Rect surfaceInsets)->
View.draw(Canvas canvas)
2.5 界面銷燬
ActivityThread中handleDestroyActivity(IBinder token, boolean finishing, int configChanges,
boolean getNonConfigInstance, String reason)
ActivityClientRecord r = performDestroyActivity(token, finishing,
configChanges, getNonConfigInstance, reason);
if (r != null) {
cleanUpPendingRemoveWindows(r, finishing);
WindowManager wm = r.activity.getWindowManager();
View v = r.activity.mDecor;
if (v != null) {
if (r.activity.mVisibleFromServer) {
mNumVisibleActivities--;
}
IBinder wtoken = v.getWindowToken();
if (r.activity.mWindowAdded) {
if (r.mPreserveWindow) {
// Hold off on removing this until the new activity's
// window is being added.
r.mPendingRemoveWindow = r.window;
r.mPendingRemoveWindowManager = wm;
// We can only keep the part of the view hierarchy that we control,
// everything else must be removed, because it might not be able to
// behave properly when activity is relaunching.
r.window.clearContentView();
} else {
wm.removeViewImmediate(v);
}
}
...
}
三、總結
主要講了PhoneWindow被添加到WindowManagerService和界面刷新銷燬的流程。
另外簡單提兩個問題，並給出提示
1.View的onAttachedToWindow()、onDetachedToWindow(）何時回調
提示：ViewRootImpl
2.頁面打開時，EditText hasFocus()時爲何會彈出輸入法
提示：View的onAttachedToWindow()方法
@CallSuper
protected void onAttachedToWindow() {
...
if (isFocused()) {
InputMethodManager imm = InputMethodManager.peekInstance();
if (imm != null) {
imm.focusIn(this);
}
}
}