Android9.0 View的绘制源码解析(一）

一.开始

在Activity的onCreate方法中setContenView后，创建了mDecorView，那么它是怎么执行onMeause，onLayout，onDraw方法的呢?我们从源码分析开始。

二.源码解析

Activity的入口是在ActivityThread执行的，我们看下ActivityThread中有handleMessage方法中RELAUNCH_ACTIVITY，执行handleRelaunchActivityLocally方法

 public void handleMessage(Message msg) {if (DEBUG_MESSAGES) Slog.v(TAG, ">>> handling: " + codeToString(msg.what));switch (msg.what) {...case RELAUNCH_ACTIVITY:handleRelaunchActivityLocally((IBinder) msg.obj);break;
}
}

该方法最后，执行了handleLaunchActivity方法，看下其方法

 public Activity handleLaunchActivity(ActivityClientRecord r,PendingTransactionActions pendingActions, Intent customIntent) {// If we are getting ready to gc after going to the background, well// we are back active so skip it.unscheduleGcIdler();mSomeActivitiesChanged = true;if (r.profilerInfo != null) {mProfiler.setProfiler(r.profilerInfo);mProfiler.startProfiling();}if (r.mPendingFixedRotationAdjustments != null) {// The rotation adjustments must be applied before handling configuration, so process// level display metrics can be adjusted.overrideApplicationDisplayAdjustments(r.token, adjustments ->adjustments.setFixedRotationAdjustments(r.mPendingFixedRotationAdjustments));}// Make sure we are running with the most recent config.handleConfigurationChanged(null, null);if (localLOGV) Slog.v(TAG, "Handling launch of " + r);// Initialize before creating the activityif (!ThreadedRenderer.sRendererDisabled&& (r.activityInfo.flags & ActivityInfo.FLAG_HARDWARE_ACCELERATED) != 0) {HardwareRenderer.preload();}WindowManagerGlobal.initialize();// Hint the GraphicsEnvironment that an activity is launching on the process.GraphicsEnvironment.hintActivityLaunch();final Activity a = performLaunchActivity(r, customIntent);if (a != null) {r.createdConfig = new Configuration(mConfiguration);reportSizeConfigurations(r);if (!r.activity.mFinished && pendingActions != null) {pendingActions.setOldState(r.state);pendingActions.setRestoreInstanceState(true);pendingActions.setCallOnPostCreate(true);}} else {// If there was an error, for any reason, tell the activity manager to stop us.try {ActivityTaskManager.getService().finishActivity(r.token, Activity.RESULT_CANCELED, null,Activity.DONT_FINISH_TASK_WITH_ACTIVITY);} catch (RemoteException ex) {throw ex.rethrowFromSystemServer();}}return a;}

其中final Activity a = performLaunchActivity(r, customIntent)，执行performLaunchActivity方法，看其详情

private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {ActivityInfo aInfo = r.activityInfo;if (r.packageInfo == null) {r.packageInfo = getPackageInfo(aInfo.applicationInfo, r.compatInfo,Context.CONTEXT_INCLUDE_CODE);}ComponentName component = r.intent.getComponent();if (component == null) {component = r.intent.resolveActivity(mInitialApplication.getPackageManager());r.intent.setComponent(component);}if (r.activityInfo.targetActivity != null) {component = new ComponentName(r.activityInfo.packageName,r.activityInfo.targetActivity);}ContextImpl appContext = createBaseContextForActivity(r);Activity activity = null;try {java.lang.ClassLoader cl = appContext.getClassLoader();activity = mInstrumentation.newActivity(cl, component.getClassName(), r.intent);StrictMode.incrementExpectedActivityCount(activity.getClass());r.intent.setExtrasClassLoader(cl);r.intent.prepareToEnterProcess();if (r.state != null) {r.state.setClassLoader(cl);}} catch (Exception e) {if (!mInstrumentation.onException(activity, e)) {throw new RuntimeException("Unable to instantiate activity " + component+ ": " + e.toString(), e);}}try {Application app = r.packageInfo.makeApplication(false, mInstrumentation);if (localLOGV) Slog.v(TAG, "Performing launch of " + r);if (localLOGV) Slog.v(TAG, r + ": app=" + app+ ", appName=" + app.getPackageName()+ ", pkg=" + r.packageInfo.getPackageName()+ ", comp=" + r.intent.getComponent().toShortString()+ ", dir=" + r.packageInfo.getAppDir());if (activity != null) {CharSequence title = r.activityInfo.loadLabel(appContext.getPackageManager());Configuration config = new Configuration(mCompatConfiguration);if (r.overrideConfig != null) {config.updateFrom(r.overrideConfig);}if (DEBUG_CONFIGURATION) Slog.v(TAG, "Launching activity "+ r.activityInfo.name + " with config " + config);Window window = null;if (r.mPendingRemoveWindow != null && r.mPreserveWindow) {window = r.mPendingRemoveWindow;r.mPendingRemoveWindow = null;r.mPendingRemoveWindowManager = null;}// Activity resources must be initialized with the same loaders as the// application context.appContext.getResources().addLoaders(app.getResources().getLoaders().toArray(new ResourcesLoader[0]));appContext.setOuterContext(activity);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, r.configCallback,r.assistToken);if (customIntent != null) {activity.mIntent = customIntent;}r.lastNonConfigurationInstances = null;checkAndBlockForNetworkAccess();activity.mStartedActivity = false;int theme = r.activityInfo.getThemeResource();if (theme != 0) {activity.setTheme(theme);}activity.mCalled = false;if (r.isPersistable()) {mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);} else {mInstrumentation.callActivityOnCreate(activity, r.state);}if (!activity.mCalled) {throw new SuperNotCalledException("Activity " + r.intent.getComponent().toShortString() +" did not call through to super.onCreate()");}r.activity = activity;mLastReportedWindowingMode.put(activity.getActivityToken(),config.windowConfiguration.getWindowingMode());}r.setState(ON_CREATE);// updatePendingActivityConfiguration() reads from mActivities to update// ActivityClientRecord which runs in a different thread. Protect modifications to// mActivities to avoid race.synchronized (mResourcesManager) {mActivities.put(r.token, r);}} catch (SuperNotCalledException e) {throw e;} catch (Exception e) {if (!mInstrumentation.onException(activity, e)) {throw new RuntimeException("Unable to start activity " + component+ ": " + e.toString(), e);}}return activity;}

 activity = mInstrumentation.newActivity( cl, component.getClassName(), r.intent);Instrumentation类执行类newActivity方法，我们看下Instrumentation中方法的实现

  public Activity newActivity(ClassLoader cl, String className,Intent intent)throws InstantiationException, IllegalAccessException,ClassNotFoundException {String pkg = intent != null && intent.getComponent() != null? intent.getComponent().getPackageName() : null;return getFactory(pkg).instantiateActivity(cl, className, intent);}

getFactory为AppComponentFactory，我们进入其方法中看

  public @NonNull Activity instantiateActivity(@NonNull ClassLoader cl, @NonNull String className,@Nullable Intent intent)throws InstantiationException, IllegalAccessException, ClassNotFoundException {return (Activity) cl.loadClass(className).newInstance();}

可见Activity是在这里建立的。既然Activity建立了，我们回到performLaunchActivity方法中，会看到

 private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {...appContext.setOuterContext(activity);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, r.configCallback,r.assistToken);
...if (r.isPersistable()) {mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);} else {mInstrumentation.callActivityOnCreate(activity, r.state);}...return activity;}

Activity建立后，执行其attach方法，后面又通过Instrumentation执行callActivityOnCreate方法，看其实现

  public void callActivityOnCreate(Activity activity, Bundle icicle) {prePerformCreate(activity);activity.performCreate(icicle);postPerformCreate(activity);}

再看Activity的performCreate方法

  final void performCreate(Bundle icicle, PersistableBundle persistentState) {dispatchActivityPreCreated(icicle);...     if (persistentState != null) {onCreate(icicle, persistentState);} else {onCreate(icicle);}}

可以看到其调用了我们熟悉的onCreate方法，这里建立了Activity和调用了attach和onCreate方法，在onCreate方法中会生成mDecorView，还未产生绘制流程，通过源码看，其绘制流程是在handleResumeActivity开始执行的，我们看下源码

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 considerationfinal ActivityClientRecord r = performResumeActivity(token, finalStateRequest, reason);if (r == null) {// We didn't actually resume the activity, so skipping any follow-up actions.return;}if (mActivitiesToBeDestroyed.containsKey(token)) {// Although the activity is resumed, it is going to be destroyed. So the following// UI operations are unnecessary and also prevents exception because its token may// be gone that window manager cannot recognize it. All necessary cleanup actions// performed below will be done while handling destruction.return;}final Activity a = r.activity;if (localLOGV) {Slog.v(TAG, "Resume " + r + " started activity: " + a.mStartedActivity+ ", hideForNow: " + r.hideForNow + ", finished: " + a.mFinished);}final int forwardBit = isForward? WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION : 0;// 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 = ActivityTaskManager.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 (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) {if (!a.mWindowAdded) {a.mWindowAdded = true;wm.addView(decor, l);} else {// The activity will get a callback for this {@link LayoutParams} change// earlier. However, at that time the decor will not be set (this is set// in this method), so no action will be taken. This call ensures the// callback occurs with the decor set.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) {if (localLOGV) Slog.v(TAG, "Launch " + r + " mStartedActivity set");r.hideForNow = true;}// Get rid of anything left hanging around.cleanUpPendingRemoveWindows(r, false /* force */);// 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);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++;if (r.activity.mVisibleFromClient) {r.activity.makeVisible();}}r.nextIdle = mNewActivities;mNewActivities = r;if (localLOGV) Slog.v(TAG, "Scheduling idle handler for " + r);Looper.myQueue().addIdleHandler(new Idler());}

其中final ActivityClientRecord r = performResumeActivity(token, finalStateRequest, reason)，我们看下performResumeActivity实现，

 public ActivityClientRecord performResumeActivity(IBinder token, boolean finalStateRequest,String reason) {...r.activity.performResume(r.startsNotResumed, reason);return r;}

再看Activity的performResume

final void performResume(boolean followedByPause, String reason) {dispatchActivityPreResumed();performRestart(true /* start */, reason);...// mResumed is set by the instrumentationmInstrumentation.callActivityOnResume(this);}

其调用了Instrumentation的callActivityOnResume方法，我们再看其实现

  public void callActivityOnResume(Activity activity) {activity.mResumed = true;activity.onResume();if (mActivityMonitors != null) {synchronized (mSync) {final int N = mActivityMonitors.size();for (int i=0; i

   @Overridepublic void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {applyDefaultToken(params);mGlobal.addView(view, params, mContext.getDisplayNoVerify(), mParentWindow,mContext.getUserId());}

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");}if (display == null) {throw new IllegalArgumentException("display must not be null");}if (!(params instanceof WindowManager.LayoutParams)) {throw new IllegalArgumentException("Params must be WindowManager.LayoutParams");}final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams) params;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);}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);}}}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 thingstry {root.setView(view, wparams, panelParentView, userId);} catch (RuntimeException e) {// BadTokenException or InvalidDisplayException, clean up.if (index >= 0) {removeViewLocked(index, true);}throw e;}}}

    public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView,int userId) {synchronized (this) {if (mView == null) {mView = view;requestLayout();...view.assignParent(this);...}}}

 @Overridepublic void requestLayout() {if (!mHandlingLayoutInLayoutRequest) {checkThread();mLayoutRequested = true;scheduleTraversals();}}

 void scheduleTraversals() {if (!mTraversalScheduled) {mTraversalScheduled = true;mTraversalBarrier = mHandler.getLooper().getQueue().postSyncBarrier();mChoreographer.postCallback(Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);notifyRendererOfFramePending();pokeDrawLockIfNeeded();}}

 final class TraversalRunnable implements Runnable {@Overridepublic void run() {doTraversal();}}

void doTraversal() {if (mTraversalScheduled) {mTraversalScheduled = false;mHandler.getLooper().getQueue().removeSyncBarrier(mTraversalBarrier);if (mProfile) {Debug.startMethodTracing("ViewAncestor");}performTraversals();if (mProfile) {Debug.stopMethodTracing();mProfile = false;}}}

private void performTraversals() {if (!mStopped || mReportNextDraw) {boolean focusChangedDueToTouchMode = ensureTouchModeLocally((relayoutResult & WindowManagerGlobal.RELAYOUT_RES_IN_TOUCH_MODE) != 0);if (focusChangedDueToTouchMode || mWidth != host.getMeasuredWidth()|| mHeight != host.getMeasuredHeight() || dispatchApplyInsets ||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()+ " dispatchApplyInsets=" + dispatchApplyInsets);// Ask host how big it wants to beperformMeasure(childWidthMeasureSpec, childHeightMeasureSpec);// Implementation of weights from WindowManager.LayoutParams// We just grow the dimensions as needed and re-measure if// needs beint width = host.getMeasuredWidth();int height = host.getMeasuredHeight();...performLayout(lp, mWidth, mHeight);...performDraw();}}}

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