Android知识总结
一、Activity的onResume流程
在ResumeActivityItem的execute方法执行
public void execute(ClientTransactionHandler client, IBinder token,
PendingTransactionActions pendingActions) {
Trace.traceBegin(TRACE_TAG_ACTIVITY_MANAGER, "activityResume");
client.handleResumeActivity(token, true /* finalStateRequest */, mIsForward,
"RESUME_ACTIVITY");
Trace.traceEnd(TRACE_TAG_ACTIVITY_MANAGER);
}
调用到了ActivityThread#handleResumeActivity方法，ActivityThread实现ClientTransactionHandler抽象类
public void handleResumeActivity(IBinder token, boolean finalStateRequest, boolean isForward,
String reason) {
// If we are getting ready to gc after going to the background, well
// we are back active so skip it.
unscheduleGcIdler();
mSomeActivitiesChanged = true;
// TODO Push resumeArgs into the activity for consideration
final ActivityClientRecord r = performResumeActivity(token, finalStateRequest, reason);
...
}
public ActivityClientRecord performResumeActivity(IBinder token, boolean finalStateRequest,
String reason) {
final ActivityClientRecord r = mActivities.get(token);
if (localLOGV) {
Slog.v(TAG, "Performing resume of " + r + " finished=" + r.activity.mFinished);
}
if (r == null || r.activity.mFinished) {
return null;
}
if (r.getLifecycleState() == ON_RESUME) {
if (!finalStateRequest) {
final RuntimeException e = new IllegalStateException(
"Trying to resume activity which is already resumed");
Slog.e(TAG, e.getMessage(), e);
Slog.e(TAG, r.getStateString());
// one, we don't expect it to happen.
}
return null;
}
if (finalStateRequest) {
r.hideForNow = false;
r.activity.mStartedActivity = false;
}
try {
r.activity.onStateNotSaved();
r.activity.mFragments.noteStateNotSaved();
checkAndBlockForNetworkAccess();
if (r.pendingIntents != null) {
deliverNewIntents(r, r.pendingIntents);
r.pendingIntents = null;
}
if (r.pendingResults != null) {
deliverResults(r, r.pendingResults, reason);
r.pendingResults = null;
}
//调用activity.performResume执行resume流程
r.activity.performResume(r.startsNotResumed, reason);
r.state = null;
r.persistentState = null;
//设置Activity的状态为ON_RESUME
r.setState(ON_RESUME);
reportTopResumedActivityChanged(r, r.isTopResumedActivity, "topWhenResuming");
} catch (Exception e) {
if (!mInstrumentation.onException(r.activity, e)) {
throw new RuntimeException("Unable to resume activity "
+ r.intent.getComponent().toShortString() + ": " + e.toString(), e);
}
}
return r;
}
然后执行Activity的performResume方法
final void performResume(boolean followedByPause, String reason) {
dispatchActivityPreResumed();
//该函数中因为mStopped = false，所以实际没有什么操作
performRestart(true /* start */, reason);
mFragments.execPendingActions();
mLastNonConfigurationInstances = null;
if (mAutoFillResetNeeded) {
//自动填充
mAutoFillIgnoreFirstResumePause = followedByPause;
if (mAutoFillIgnoreFirstResumePause && DEBUG_LIFECYCLE) {
Slog.v(TAG, "autofill will ignore first pause when relaunching " + this);
}
}
mCalled = false;
// 调用Instrumentation.callActivityOnResume执行onResume流程
mInstrumentation.callActivityOnResume(this);
EventLogTags.writeWmOnResumeCalled(mIdent, getComponentName().getClassName(), reason);
if (!mCalled) {
throw new SuperNotCalledException(
"Activity " + mComponent.toShortString() +
" did not call through to super.onResume()");
}
// invisible activities must be finished before onResume() completes
if (!mVisibleFromClient && !mFinished) {
Log.w(TAG, "An activity without a UI must call finish() before onResume() completes");
if (getApplicationInfo().targetSdkVersion
> android.os.Build.VERSION_CODES.LOLLIPOP_MR1) {
throw new IllegalStateException(
"Activity " + mComponent.toShortString() +
" did not call finish() prior to onResume() completing");
}
}
// Now really resume, and install the current status bar and menu.
mCalled = false;
mFragments.dispatchResume();
mFragments.execPendingActions();
onPostResume();
if (!mCalled) {
throw new SuperNotCalledException(
"Activity " + mComponent.toShortString() +
" did not call through to super.onPostResume()");
}
dispatchActivityPostResumed();
}
调用Instrumentation中的callActivityOnResume的方法
public void callActivityOnResume(Activity activity) {
activity.mResumed = true;
//调用Activity的onResume函数
activity.onResume();
if (mActivityMonitors != null) {
synchronized (mSync) {
final int N = mActivityMonitors.size();
for (int i=0; i至此，Activity的onResume函数被调用了。
二、View 添到 ViewRootImpl 流程
入口handleResumeActivity@ActivityThread方法
@Override
public void handleResumeActivity(IBinder token, boolean finalStateRequest, boolean isForward, String reason) {
final Activity a = r.activity;
...
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(); //WindowManagerImpl
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;
ViewRootImpl impl = decor.getViewRootImpl();
if (impl != null) {
impl.notifyChildRebuilt();
}
}
if (a.mVisibleFromClient) {
if (!a.mWindowAdded) {
a.mWindowAdded = true;
//添加View到Win，但是这个时候，还是不可见的
wm.addView(decor, l);
} else {
a.onWindowAttributesChanged(l);
}
}
} else if (!willBeVisible) {
if (localLOGV) Slog.v(TAG, "Launch " + r + " mStartedActivity set");
r.hideForNow = true;
}
if (!r.activity.mFinished && willBeVisible && r.activity.mDecor != null && !r.hideForNow) {
if (r.newConfig != null) {
performConfigurationChangedForActivity(r, r.newConfig);
if (DEBUG_CONFIGURATION) {
Slog.v(TAG, "Resuming activity " + r.activityInfo.name + " with newConfig "
+ r.activity.mCurrentConfig);
}
r.newConfig = null;
}
if (localLOGV) Slog.v(TAG, "Resuming " + r + " with isForward=" + isForward);
ViewRootImpl impl = r.window.getDecorView().getViewRootImpl();
WindowManager.LayoutParams l = impl != null
? impl.mWindowAttributes : 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++;
//在这里，执行了重要的操作,使得 DecorView 可见
if (r.activity.mVisibleFromClient) {
r.activity.makeVisible();
}
}
Looper.myQueue().addIdleHandler(new Idler());
}
执行Activity#makeVisible使View处于可见状态
void makeVisible() {
if (!mWindowAdded) {
ViewManager wm = getWindowManager();
wm.addView(mDecor, getWindow().getAttributes());
mWindowAdded = true;
}
//设置DecorView可见
mDecor.setVisibility(View.VISIBLE);
}
执行WindowManagerImpl的addView方法
public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
applyDefaultToken(params);
mGlobal.addView(view, params, mContext.getDisplayNoVerify(), mParentWindow, mContext.getUserId());
}
执行WindowManagerGlobal的addView方法
private final ArrayList mViews = new ArrayList();
@UnsupportedAppUsage
private final ArrayList mRoots = new ArrayList();
@UnsupportedAppUsage
private final ArrayList mParams = new ArrayList();
private final ArraySet mDyingViews = new ArraySet();
public void addView(View view, ViewGroup.LayoutParams params,
Display display, Window parentWindow, int userId) {
if (view == null) {
throw new IllegalArgumentException("view must not be null");
}
final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams) params;
//如果当前窗口需要被添加为另一个窗口的附属窗口（子窗口），则需要让父窗口视自己的情况
//对当前窗口的布局参数(LayoutParams)进行一些修改
if (parentWindow != null) {
parentWindow.adjustLayoutParamsForSubWindow(wparams);
} else {
// If there's no parent, then hardware acceleration for this view is
// set from the application's hardware acceleration setting.
final Context context = view.getContext();
if (context != null
&& (context.getApplicationInfo().flags
& ApplicationInfo.FLAG_HARDWARE_ACCELERATED) != 0) {
wparams.flags |= WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED;
}
}
ViewRootImpl root;
View panelParentView = null;
synchronized (mLock) {
// Start watching for system property changes.
if (mSystemPropertyUpdater == null) {
mSystemPropertyUpdater = new Runnable() {
@Override public void run() {
synchronized (mLock) {
for (int i = mRoots.size() - 1; i >= 0; --i) {
mRoots.get(i).loadSystemProperties();
}
}
}
};
SystemProperties.addChangeCallback(mSystemPropertyUpdater);
}
//WindowManager不允许同一个View被添加两次
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.
}
// If this is a panel window, then find the window it is being
// attached to for future reference.
if (wparams.type >= WindowManager.LayoutParams.FIRST_SUB_WINDOW &&
wparams.type <= WindowManager.LayoutParams.LAST_SUB_WINDOW) {
final int count = mViews.size();
for (int i = 0; i < count; i++) {
if (mRoots.get(i).mWindow.asBinder() == wparams.token) {
panelParentView = mViews.get(i);
}
}
}
//创建一个ViewRootImpl对象并保存在root变量中
root = new ViewRootImpl(view.getContext(), display);
view.setLayoutParams(wparams);
//将作为窗口的控件、布局参数以及新建的ViewRootImpl以相同的索引值保存在三个数组中
mViews.add(view); //DecorView
mRoots.add(root); //ViewRootImpl
mParams.add(wparams); //WindowManager.LayoutParams
// do this last because it fires off messages to start doing things
try {
//将作为窗口的控件设置给ViewRootImpl
//这个动作将导致ViewRootImpl向WMS添加新的窗口、申请Surface以及托管控件在Surface上的重绘动作。
//这才是真正意义上完成了窗口的添加操作
root.setView(view, wparams, panelParentView, userId);
} catch (RuntimeException e) {
// BadTokenException or InvalidDisplayException, clean up.
if (index >= 0) {
removeViewLocked(index, true);
}
throw e;
}
}
}
ViewRootImpl实现了一个控件树的根。它负责与WMS进行直接的通讯，负责管理Surface，负责触发控件的测量与布局，负责触发控件的绘制，同时也是输入事件的中转站。总之，ViewRootImpl是整个控件系统正常运转的动力所在，无疑是本章最关键的一个组件。
另外，mViews、mParams以及mRoots这三个数组的容量是随着当前进程中的窗口数量的变化而变化的。因此在addView()以及随后的removeView()中都伴随着数组的新建、拷贝等操作。鉴于一个进程所添加的窗口数量不会太多，而且也不会很频繁，所以这些时间开销是可以接受的。
调用ViewRootImpl.setView()函数，将控件交给ViewRootImpl进行托管。这个动作将使得ViewRootImpl向WMS添加窗口、获取Surface以及重绘等一系列的操作。这一步是控件能够作为一个窗口显示在屏幕上的根本原因！
总体来说，WindowManagerGlobal在通过父窗口调整了布局参数之后，将新建的ViewRootImpl、控件以及布局参数保存在自己的三个数组中，然后将控件交由新建的ViewRootImpl进行托管，从而完成了窗口的添加。
WindowManagerGlobal的窗口管理
三个类关系图
WindowManagerImpl、WindowManagerGlobal、ViewRootImpl
WindowManagerImpl：确定 View 属于哪个屏幕，哪个父窗口WindowManagerGlobal：管理整个进程，所有的窗口信息ViewRootImpl：WindowManagerGlobal 实际操作者，操作自己的窗口和WMS进行交互
三ViewRootImpl
ViewRootImpl的构造方法
public ViewRootImpl(Context context, Display display, IWindowSession session,
boolean useSfChoreographer) {
mContext = context;
mWindowSession = session;
mDisplay = display;
mBasePackageName = context.getBasePackageName();
// 拿到创建它的线程，MainThread --- 默认
mThread = Thread.currentThread();
mLocation = new WindowLeaked(null);
mLocation.fillInStackTrace();
mWidth = -1;
mHeight = -1;
// 脏区域，就是需要绘制的区域
mDirty = new Rect();
mTempRect = new Rect();
mVisRect = new Rect();
mWinFrame = new Rect();
mWindow = new W(this);
mLeashToken = new Binder();
mTargetSdkVersion = context.getApplicationInfo().targetSdkVersion;
mViewVisibility = View.GONE;
mTransparentRegion = new Region();
mPreviousTransparentRegion = new Region();
mFirst = true; // true for the first time the view is added
mPerformContentCapture = true; // also true for the first time the view is added
mAdded = false;
// 保存当前窗口的一些信息
mAttachInfo = new View.AttachInfo(mWindowSession, mWindow, display, this, mHandler, this,
context);
....
}
调用ViewRootImpl#setView方法
public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView,
int userId) {
synchronized (this) {
if (mView == null) {
mView = view;
mAttachInfo.mDisplayState = mDisplay.getState();
mDisplayManager.registerDisplayListener(mDisplayListener, mHandler);
mViewLayoutDirectionInitial = mView.getRawLayoutDirection();
mFallbackEventHandler.setView(view);
mWindowAttributes.copyFrom(attrs);
if (mWindowAttributes.packageName == null) {
mWindowAttributes.packageName = mBasePackageName;
}
mWindowAttributes.privateFlags |=
WindowManager.LayoutParams.PRIVATE_FLAG_USE_BLAST;
attrs = mWindowAttributes;
setTag();
// Keep track of the actual window flags supplied by the client.
mClientWindowLayoutFlags = attrs.flags;
setAccessibilityFocus(null, null);
if (view instanceof RootViewSurfaceTaker) {
mSurfaceHolderCallback =
((RootViewSurfaceTaker)view).willYouTakeTheSurface();
if (mSurfaceHolderCallback != null) {
mSurfaceHolder = new TakenSurfaceHolder();
mSurfaceHolder.setFormat(PixelFormat.UNKNOWN);
mSurfaceHolder.addCallback(mSurfaceHolderCallback);
}
}
// Compute surface insets required to draw at specified Z value.
// TODO: Use real shadow insets for a constant max Z.
if (!attrs.hasManualSurfaceInsets) {
attrs.setSurfaceInsets(view, false /*manual*/, true /*preservePrevious*/);
}
CompatibilityInfo compatibilityInfo =
mDisplay.getDisplayAdjustments().getCompatibilityInfo();
mTranslator = compatibilityInfo.getTranslator();
// If the application owns the surface, don't enable hardware acceleration
if (mSurfaceHolder == null) {
// While this is supposed to enable only, it can effectively disable
// the acceleration too.
enableHardwareAcceleration(attrs);
final boolean useMTRenderer = MT_RENDERER_AVAILABLE
&& mAttachInfo.mThreadedRenderer != null;
if (mUseMTRenderer != useMTRenderer) {
// Shouldn't be resizing, as it's done only in window setup,
// but end just in case.
endDragResizing();
mUseMTRenderer = useMTRenderer;
}
}
boolean restore = false;
if (mTranslator != null) {
mSurface.setCompatibilityTranslator(mTranslator);
restore = true;
attrs.backup();
mTranslator.translateWindowLayout(attrs);
}
if (DEBUG_LAYOUT) Log.d(mTag, "WindowLayout in setView:" + attrs);
if (!compatibilityInfo.supportsScreen()) {
attrs.privateFlags |= WindowManager.LayoutParams.PRIVATE_FLAG_COMPATIBLE_WINDOW;
mLastInCompatMode = true;
}
mSoftInputMode = attrs.softInputMode;
mWindowAttributesChanged = true;
mAttachInfo.mRootView = view;
mAttachInfo.mScalingRequired = mTranslator != null;
mAttachInfo.mApplicationScale =
mTranslator == null ? 1.0f : mTranslator.applicationScale;
if (panelParentView != null) {
mAttachInfo.mPanelParentWindowToken
= panelParentView.getApplicationWindowToken();
}
mAdded = true;
int res; /* = WindowManagerImpl.ADD_OKAY; */
//请求遍历
requestLayout();
//输入事件的渠道
InputChannel inputChannel = null;
if ((mWindowAttributes.inputFeatures
& WindowManager.LayoutParams.INPUT_FEATURE_NO_INPUT_CHANNEL) == 0) {
inputChannel = new InputChannel();
}
mForceDecorViewVisibility = (mWindowAttributes.privateFlags
& PRIVATE_FLAG_FORCE_DECOR_VIEW_VISIBILITY) != 0;
try {
mOrigWindowType = mWindowAttributes.type;
mAttachInfo.mRecomputeGlobalAttributes = true;
collectViewAttributes();
adjustLayoutParamsForCompatibility(mWindowAttributes);
//将窗口添加到WMS上面 WindowManagerService
res = mWindowSession.addToDisplayAsUser(mWindow, mSeq, mWindowAttributes,
getHostVisibility(), mDisplay.getDisplayId(), userId, mTmpFrame,
mAttachInfo.mContentInsets, mAttachInfo.mStableInsets,
mAttachInfo.mDisplayCutout, inputChannel,
mTempInsets, mTempControls);
setFrame(mTmpFrame);
} catch (RemoteException e) {
mAdded = false;
mView = null;
mAttachInfo.mRootView = null;
inputChannel = null;
mFallbackEventHandler.setView(null);
unscheduleTraversals();
setAccessibilityFocus(null, null);
throw new RuntimeException("Adding window failed", e);
} finally {
if (restore) {
attrs.restore();
}
}
if (mTranslator != null) {
mTranslator.translateRectInScreenToAppWindow(mAttachInfo.mContentInsets);
}
mPendingDisplayCutout.set(mAttachInfo.mDisplayCutout);
mAttachInfo.mAlwaysConsumeSystemBars =
(res & WindowManagerGlobal.ADD_FLAG_ALWAYS_CONSUME_SYSTEM_BARS) != 0;
mPendingAlwaysConsumeSystemBars = mAttachInfo.mAlwaysConsumeSystemBars;
mInsetsController.onStateChanged(mTempInsets);
mInsetsController.onControlsChanged(mTempControls);
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");
case WindowManagerGlobal.ADD_INVALID_USER:
throw new WindowManager.BadTokenException("Unable to add Window "
+ mWindow + " -- requested userId is not valid");
}
throw new RuntimeException(
"Unable to add window -- unknown error code " + res);
}
if ((res & WindowManagerGlobal.ADD_FLAG_USE_BLAST) != 0) {
mUseBLASTAdapter = true;
}
if ((res & WindowManagerGlobal.ADD_FLAG_USE_TRIPLE_BUFFERING) != 0) {
mEnableTripleBuffering = true;
}
if (view instanceof RootViewSurfaceTaker) {
mInputQueueCallback =
((RootViewSurfaceTaker)view).willYouTakeTheInputQueue();
}
if (inputChannel != null) {
if (mInputQueueCallback != null) {
mInputQueue = new InputQueue();
mInputQueueCallback.onInputQueueCreated(mInputQueue);
}
//创建接收事件(click)
mInputEventReceiver = new WindowInputEventReceiver(inputChannel,
Looper.myLooper());
}
//给View设置父容器(ViewRootImpl)，getParent 获取最顶层父容器为 ViewRootImpl
view.assignParent(this);
mAddedTouchMode = (res & WindowManagerGlobal.ADD_FLAG_IN_TOUCH_MODE) != 0;
mAppVisible = (res & WindowManagerGlobal.ADD_FLAG_APP_VISIBLE) != 0;
if (mAccessibilityManager.isEnabled()) {
mAccessibilityInteractionConnectionManager.ensureConnection();
}
if (view.getImportantForAccessibility() == View.IMPORTANT_FOR_ACCESSIBILITY_AUTO) {
view.setImportantForAccessibility(View.IMPORTANT_FOR_ACCESSIBILITY_YES);
}
// Set up the input pipeline.
CharSequence counterSuffix = attrs.getTitle();
//事件处理
mSyntheticInputStage = new SyntheticInputStage();
InputStage viewPostImeStage = new ViewPostImeInputStage(mSyntheticInputStage);
InputStage nativePostImeStage = new NativePostImeInputStage(viewPostImeStage,
"aq:native-post-ime:" + counterSuffix);
InputStage earlyPostImeStage = new EarlyPostImeInputStage(nativePostImeStage);
InputStage imeStage = new ImeInputStage(earlyPostImeStage,
"aq:ime:" + counterSuffix);
InputStage viewPreImeStage = new ViewPreImeInputStage(imeStage);
InputStage nativePreImeStage = new NativePreImeInputStage(viewPreImeStage,
"aq:native-pre-ime:" + counterSuffix);
mFirstInputStage = nativePreImeStage;
mFirstPostImeInputStage = earlyPostImeStage;
mPendingInputEventQueueLengthCounterName = "aq:pending:" + counterSuffix;
if (mView instanceof RootViewSurfaceTaker) {
PendingInsetsController pendingInsetsController =
((RootViewSurfaceTaker) mView).providePendingInsetsController();
if (pendingInsetsController != null) {
pendingInsetsController.replayAndAttach(mInsetsController);
}
}
}
}
}
setView 重点总结
- 1、requestLayout ：遍历绘制 View
- 2、mWindowSession.addToDisplayAsUser ：把当前窗口添加到WMS上
- 3、事件处理
- 4、view.assignParent(this) ：设置View的父容器为 ViewRootImpl
执行ViewRootImpl#requestLayout请求遍历
public void requestLayout() {
if (!mHandlingLayoutInLayoutRequest) {
checkThread();
mLayoutRequested = true;
scheduleTraversals();
}
}
void scheduleTraversals() {
//设置一个成员变量，标明是否正在执行
if (!mTraversalScheduled) {
//标记位设置为true，避免重复执行
mTraversalScheduled = true;
//添加同步屏障，目的是屏蔽同步消息
mTraversalBarrier = mHandler.getLooper().getQueue().postSyncBarrier();
mChoreographer.postCallback(
Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);
notifyRendererOfFramePending();
pokeDrawLockIfNeeded();
}
}
执行Choreographer里面postCallback方法发送消息
public void postCallback(int callbackType, Runnable action, Object token) {
postCallbackDelayed(callbackType, action, token, 0);
}
public void postCallbackDelayed(int callbackType,
Runnable action, Object token, long delayMillis) {
if (action == null) {
throw new IllegalArgumentException("action must not be null");
}
if (callbackType < 0 || callbackType > CALLBACK_LAST) {
throw new IllegalArgumentException("callbackType is invalid");
}
postCallbackDelayedInternal(callbackType, action, token, delayMillis);
}
private void postCallbackDelayedInternal(int callbackType,
Object action, Object token, long delayMillis) {
if (DEBUG_FRAMES) {
Log.d(TAG, "PostCallback: type=" + callbackType
+ ", action=" + action + ", token=" + token
+ ", delayMillis=" + delayMillis);
}
synchronized (mLock) {
final long now = SystemClock.uptimeMillis();
final long dueTime = now + delayMillis;
mCallbackQueues[callbackType].addCallbackLocked(dueTime, action, token);
if (dueTime <= now) {
scheduleFrameLocked(now);
} else {
Message msg = mHandler.obtainMessage(MSG_DO_SCHEDULE_CALLBACK, action);
msg.arg1 = callbackType;
//设置异步消息
msg.setAsynchronous(true);
mHandler.sendMessageAtTime(msg, dueTime);
}
}
}
最后会回调到ViewRootImpl中的内部类TraversalRunnable中，TraversalRunnable实现了 Runnable事务
final class TraversalRunnable implements Runnable {
@Override
public void run() {
doTraversal();
}
}
然后执行ViewRootImpl#doTraversal方法
void doTraversal() {
if (mTraversalScheduled) {
//将在上面scheduleTraversals()方法中设置的标记为置为false
mTraversalScheduled = false;
//移除同步屏障（使用添加同步屏障的时候返回的mTraversalBarrier变量）
mHandler.getLooper().getQueue().removeSyncBarrier(mTraversalBarrier);
if (mProfile) {
Debug.startMethodTracing("ViewAncestor");
}
// 开始绘制View
performTraversals();
if (mProfile) {
Debug.stopMethodTracing();
mProfile = false;
}
}
}
下面的流程建下章：View 绘制流程(二)
总结：有handleResumeActivity@ActivityThread方法可得，onResume 在 addView（View 的添加）之前执行，所以第一次执行 onResume 时在里面度量View的宽高是无效的。