View 绘制流程(一)

Android知识总结

一、Activity的onResume流程

ResumeActivityItemexecute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ActivityperformResume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WindowManagerImpladdView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WindowManagerGlobaladdView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,onResumeaddView(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。

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