从头到尾给你讲明白Android View实现原理

public void setContentView(@LayoutRes int layoutResID) {
        getWindow().setContentView(layoutResID);
        initWindowDecorActionBar();
    }

public Window getWindow() {
        return mWindow;
    }

 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) {
        attachBaseContext(context);
        mFragments.attachHost(null /*parent*/);
        mWindow = new PhoneWindow(this, window);
        mWindow.setWindowControllerCallback(this);
        mWindow.setCallback(this);
        mWindow.setOnWindowDismissedCallback(this);
        mWindow.getLayoutInflater().setPrivateFactory(this);
        ...省略一些代码
        //调用WindowManagerImpl.createLocalWindowManager返回WindowManagerImpl
        mWindow.setWindowManager(
                (WindowManager)context.getSystemService(Context.WINDOW_SERVICE),
                mToken, mComponent.flattenToString(),
                (info.flags & ActivityInfo.FLAG_HARDWARE_ACCELERATED) != 0);
        if (mParent != null) {
            //如果mParent不为空
            mWindow.setContainer(mParent.getWindow());
        }
        mWindowManager = mWindow.getWindowManager();
    }

 @Override
    public void setContentView(int layoutResID) {
        //如果mContentParent==null初始化DecorView
        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);
        }
        mContentParent.requestApplyInsets();
        final Callback cb = getCallback();
        if (cb != null && !isDestroyed()) {
            cb.onContentChanged();
        }
        mContentParentExplicitlySet = true;
    }

private void installDecor() {
        mForceDecorInstall = false;
        if (mDecor == null) {
            //return new DecorView
            mDecor = generateDecor(-1);
            mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
            mDecor.setIsRootNamespace(true);
            if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {
                mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);
            }
        } else {
            mDecor.setWindow(this);
        }
        //如果mContentParent==null 初始化mContentParent
        if (mContentParent == null) {
            mContentParent = generateLayout(mDecor);
            ...省略代码
            }
        }
    }

public void setWindowManager(WindowManager wm, IBinder appToken, String appName,
            boolean hardwareAccelerated) {
        mAppToken = appToken;
        mAppName = appName;
        mHardwareAccelerated = hardwareAccelerated
                || SystemProperties.getBoolean(PROPERTY_HARDWARE_UI, false);
        if (wm == null) {
            wm = (WindowManager)mContext.getSystemService(Context.WINDOW_SERVICE);
        }
        mWindowManager = ((WindowManagerImpl)wm).createLocalWindowManager(this);
    }

public WindowManagerImpl createLocalWindowManager(Window parentWindow) {
        return new WindowManagerImpl(mContext, parentWindow);
    }

public final class WindowManagerImpl implements WindowManager {
    private final WindowManagerGlobal mGlobal = WindowManagerGlobal.getInstance();
    private final Context mContext;
    private final Window mParentWindow;
     public WindowManagerImpl createLocalWindowManager(Window parentWindow) {
        return new WindowManagerImpl(mContext, parentWindow);
    }
    @Override
    public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
        applyDefaultToken(params);
        mGlobal.addView(view, params, mContext.getDisplay(), mParentWindow);
    }
    @Override
    public void updateViewLayout(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
        applyDefaultToken(params);
        mGlobal.updateViewLayout(view, params);
    }
    @Override
    public void removeView(View view) {
        mGlobal.removeView(view, false);
    }
}

public final class WindowManagerGlobal {
    private static final String TAG = "WindowManager";
    //WindowManagerGlobal单例对象
    private static WindowManagerGlobal sDefaultWindowManager;
    //WindowManagerService在客户端的远程代理对象
    private static IWindowManager sWindowManagerService;
    //单个App客户端与WindowManagerService对应的一个IWindowSession
    private static IWindowSession sWindowSession;
    private final Object mLock = new Object();
    //App进程中所有Activity的DecorView
    private final ArrayList<View> mViews = new ArrayList<View>();
    //App进程中所有Activity的DecorView对应的ViewRootImpl
    private final ArrayList<ViewRootImpl> mRoots = new ArrayList<ViewRootImpl>();
    private final ArrayList<WindowManager.LayoutParams> mParams =
            new ArrayList<WindowManager.LayoutParams>();
    //要结束生命的Views
    private final ArraySet<View> mDyingViews = new ArraySet<View>();
    private Runnable mSystemPropertyUpdater;
    private WindowManagerGlobal() {
    }
    public static void initialize() {
        getWindowManagerService();
    }
    public static WindowManagerGlobal getInstance() {
        synchronized (WindowManagerGlobal.class) {
            if (sDefaultWindowManager == null) {
                sDefaultWindowManager = new WindowManagerGlobal();
            }
            return sDefaultWindowManager;
        }
    }
    /**获取WindowMangerService在APP进程端的远程对象**/
    public static IWindowManager getWindowManagerService() {
        synchronized (WindowManagerGlobal.class) {
            if (sWindowManagerService == null) {
                sWindowManagerService = IWindowManager.Stub.asInterface(
                        ServiceManager.getService("window"));
                try {
                    sWindowManagerService = getWindowManagerService();
                    ValueAnimator.setDurationScale(sWindowManagerService.getCurrentAnimatorScale());
                } catch (RemoteException e) {
                    throw e.rethrowFromSystemServer();
                }
            }
            return sWindowManagerService;
        }
    }
    /**
    *   1.如果view已经被add了，报错
    *   2.创建ViewRootImpl，调用ViewRootImpl.setView
    **/
    public void addView(View view, ViewGroup.LayoutParams params,
            Display display, Window parentWindow) {
        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 things
        try {
            root.setView(view, wparams, panelParentView);
        } catch (RuntimeException e) {
            // BadTokenException or InvalidDisplayException, clean up.
            synchronized (mLock) {
                final int index = findViewLocked(view, false);
                if (index >= 0) {
                    removeViewLocked(index, true);
                }
            }
            throw e;
        }
    }
    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);
        }
    }
    public void removeView(View view, boolean immediate) {
        if (view == null) {
            throw new IllegalArgumentException("view must not be null");
        }
        synchronized (mLock) {
            int index = findViewLocked(view, true);
            View curView = mRoots.get(index).getView();
            removeViewLocked(index, immediate);
            if (curView == view) {
                return;
            }
            throw new IllegalStateException("Calling with view " + view
                    + " but the ViewAncestor is attached to " + curView);
        }
    }
    private void removeViewLocked(int index, boolean immediate) {
        ViewRootImpl root = mRoots.get(index);
        View view = root.getView();
        if (view != null) {
            InputMethodManager imm = InputMethodManager.getInstance();
            if (imm != null) {
                imm.windowDismissed(mViews.get(index).getWindowToken());
            }
        }
        boolean deferred = root.die(immediate);
        if (view != null) {
            view.assignParent(null);
            if (deferred) {
                mDyingViews.add(view);
            }
        }
    }
    void doRemoveView(ViewRootImpl root) {
        synchronized (mLock) {
            final int index = mRoots.indexOf(root);
            if (index >= 0) {
                mRoots.remove(index);
                mParams.remove(index);
                final View view = mViews.remove(index);
                mDyingViews.remove(view);
            }
        }
        if (ThreadedRenderer.sTrimForeground && ThreadedRenderer.isAvailable()) {
            doTrimForeground();
        }
    }
    private int findViewLocked(View view, boolean required) {
        final int index = mViews.indexOf(view);
        if (required && index < 0) {
            throw new IllegalArgumentException("View=" + view + " not attached to window manager");
        }
        return index;
    }
}

final void handleResumeActivity(IBinder token,
            boolean clearHide, boolean isForward, boolean reallyResume, int seq, String reason) {
        ActivityClientRecord r = mActivities.get(token);
        if (!checkAndUpdateLifecycleSeq(seq, r, "resumeActivity")) {
            return;
        }
        // If we are getting ready to gc after going to the background, well
        // we are back active so skip it.
        unscheduleGcIdler();
        mSomeActivitiesChanged = true;
        //调用Activity的onResume方法
        r = performResumeActivity(token, clearHide, reason);
        if (r != null) {
            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;
            //如果不可见说明在启动另一个Activity
            if (!willBeVisible) {
                try {
                    willBeVisible = ActivityManagerNative.getDefault().willActivityBeVisible(
                            a.getActivityToken());
                } catch (RemoteException e) {
                    throw e.rethrowFromSystemServer();
                }
            }
            if (r.window == null && !a.mFinished && willBeVisible) {
                //PhoneWindow 在Activity的attach中初始化的
                r.window = r.activity.getWindow();
                View decor = r.window.getDecorView();
                //刚开始的时候 设置成不可见
                decor.setVisibility(View.INVISIBLE);
                //返回的是WindowManagerImpl
                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();
                    // 第一次应该是为null
                    if (impl != null) {
                        impl.notifyChildRebuilt();
                    }
                }
                if (a.mVisibleFromClient && !a.mWindowAdded) {
                    a.mWindowAdded = true;
                    //这里会把decor加载到WindowManagerImpl中
                    wm.addView(decor, 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, REPORT_TO_ACTIVITY);
                    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);
                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();
                }
            }
            if (!r.onlyLocalRequest) {
                r.nextIdle = mNewActivities;
                mNewActivities = r;
                if (localLOGV) Slog.v(
                    TAG, "Scheduling idle handler for " + r);
                Looper.myQueue().addIdleHandler(new Idler());
            }
            r.onlyLocalRequest = false;
            // Tell the activity manager we have resumed.
            if (reallyResume) {
                try {
                    ActivityManagerNative.getDefault().activityResumed(token);
                } catch (RemoteException ex) {
                    throw ex.rethrowFromSystemServer();
                }
            }
        } else {
            // If an exception was thrown when trying to resume, then
            // just end this activity.
            try {
                ActivityManagerNative.getDefault()
                    .finishActivity(token, Activity.RESULT_CANCELED, null,
                            Activity.DONT_FINISH_TASK_WITH_ACTIVITY);
            } catch (RemoteException ex) {
                throw ex.rethrowFromSystemServer();
            }
        }
    }

public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
        synchronized (this) {
            //如果mView==null 表示是新增加的
            if (mView == null) {
                mView = view;
                ...省略
                requestLayout();
                try {
                    mOrigWindowType = mWindowAttributes.type;
                    mAttachInfo.mRecomputeGlobalAttributes = true;
                    collectViewAttributes();
                    res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
                            getHostVisibility(), mDisplay.getDisplayId(),
                            mAttachInfo.mContentInsets, mAttachInfo.mStableInsets,
                            mAttachInfo.mOutsets, 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 (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);
                }
            }
        }
    }

 @Override
    public void requestLayout() {
        if (!mHandlingLayoutInLayoutRequest) {
            checkThread();
            //注意这个变量
            mLayoutRequested = true;
            scheduleTraversals();
        }
    }

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

final class TraversalRunnable implements Runnable {
        @Override
        public 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() {
        // cache mView since it is used so much below...
        final View host = mView;
        if (DBG) {
            System.out.println("======================================");
            System.out.println("performTraversals");
            host.debug();
        }
        if (host == null || !mAdded)
            return;
        //正在遍历
        mIsInTraversal = true;
        //马上要画
        mWillDrawSoon = true;
        //windowSize是否改变
        boolean windowSizeMayChange = false;
        boolean newSurface = false;
        boolean surfaceChanged = false;
        WindowManager.LayoutParams lp = mWindowAttributes;
        //预期的window的宽度
        int desiredWindowWidth;
        int desiredWindowHeight;
        //当前View是否可见
        final int viewVisibility = getHostVisibility();
        //view的可见性是否改变(1.不是第一次而且和上次的可见性不一样)
        final boolean viewVisibilityChanged = !mFirst
                && (mViewVisibility != viewVisibility || mNewSurfaceNeeded);
        //用户肉眼看到的View的可见性是否改变
        final boolean viewUserVisibilityChanged = !mFirst &&
                ((mViewVisibility == View.VISIBLE) != (viewVisibility == View.VISIBLE));
        ...省略代码
        Rect frame = mWinFrame;
        if (mFirst) {
            //如果是第一次
            mFullRedrawNeeded = true;
            //需要请求layout
            mLayoutRequested = true;
            //如果是状态栏或者输入法 需要使用真实的size
            if (shouldUseDisplaySize(lp)) {
                // NOTE -- system code, won't try to do compat mode.
                Point size = new Point();
                mDisplay.getRealSize(size);
                desiredWindowWidth = size.x;
                desiredWindowHeight = size.y;
            } else {
                Configuration config = mContext.getResources().getConfiguration();
                desiredWindowWidth = dipToPx(config.screenWidthDp);
                desiredWindowHeight = dipToPx(config.screenHeightDp);
            }
            ...省略代码
            //如果是第一次 会调用View的onAttachedToWindow
            host.dispatchAttachedToWindow(mAttachInfo, 0);
            mAttachInfo.mTreeObserver.dispatchOnWindowAttachedChange(true);
            dispatchApplyInsets(host);
            //Log.i(mTag, "Screen on initialized: " + attachInfo.mKeepScreenOn);
        } else {
            desiredWindowWidth = frame.width();
            desiredWindowHeight = frame.height();
            if (desiredWindowWidth != mWidth || desiredWindowHeight != mHeight) {
                if (DEBUG_ORIENTATION) Log.v(mTag, "View " + host + " resized to: " + frame);
                mFullRedrawNeeded = true;
                mLayoutRequested = true;
                windowSizeMayChange = true;
            }
        }
        if (viewVisibilityChanged) {//如果hostView的可见性变了 说明window的可见性变了
            mAttachInfo.mWindowVisibility = viewVisibility;
            host.dispatchWindowVisibilityChanged(viewVisibility);
            if (viewUserVisibilityChanged) {//如果肉眼可见性变了
                host.dispatchVisibilityAggregated(viewVisibility == View.VISIBLE);
            }
            if (viewVisibility != View.VISIBLE || mNewSurfaceNeeded) {
                endDragResizing();
                destroyHardwareResources();
            }
            if (viewVisibility == View.GONE) {
                // After making a window gone, we will count it as being
                // shown for the first time the next time it gets focus.
                mHasHadWindowFocus = false;
            }
        }
        // Non-visible windows can't hold accessibility focus.
        if (mAttachInfo.mWindowVisibility != View.VISIBLE) {
            //如果window不可见把Accessibility clear掉
            host.clearAccessibilityFocus();
        }
        // Execute enqueued actions on every traversal in case a detached view enqueued an action
        getRunQueue().executeActions(mAttachInfo.mHandler);
        boolean insetsChanged = false;
        boolean layoutRequested = mLayoutRequested && (!mStopped || mReportNextDraw);
        //如果是requestLayout
        if (layoutRequested) {
            final Resources res = mView.getContext().getResources();
            if (mFirst) {
                // make sure touch mode code executes by setting cached value
                // to opposite of the added touch mode.
                mAttachInfo.mInTouchMode = !mAddedTouchMode;
                ensureTouchModeLocally(mAddedTouchMode);
            } else {
                if (!mPendingOverscanInsets.equals(mAttachInfo.mOverscanInsets)) {
                    insetsChanged = true;
                }
                if (!mPendingContentInsets.equals(mAttachInfo.mContentInsets)) {
                    insetsChanged = true;
                }
                if (!mPendingStableInsets.equals(mAttachInfo.mStableInsets)) {
                    insetsChanged = true;
                }
                if (!mPendingVisibleInsets.equals(mAttachInfo.mVisibleInsets)) {
                    mAttachInfo.mVisibleInsets.set(mPendingVisibleInsets);
                    if (DEBUG_LAYOUT) Log.v(mTag, "Visible insets changing to: "
                            + mAttachInfo.mVisibleInsets);
                }
                if (!mPendingOutsets.equals(mAttachInfo.mOutsets)) {
                    insetsChanged = true;
                }
                if (mPendingAlwaysConsumeNavBar != mAttachInfo.mAlwaysConsumeNavBar) {
                    insetsChanged = true;
                }
                if (lp.width == ViewGroup.LayoutParams.WRAP_CONTENT
                        || lp.height == ViewGroup.LayoutParams.WRAP_CONTENT) {
                    windowSizeMayChange = true;
                    if (shouldUseDisplaySize(lp)) {
                        // NOTE -- system code, won't try to do compat mode.
                        Point size = new Point();
                        mDisplay.getRealSize(size);
                        desiredWindowWidth = size.x;
                        desiredWindowHeight = size.y;
                    } else {
                        Configuration config = res.getConfiguration();
                        desiredWindowWidth = dipToPx(config.screenWidthDp);
                        desiredWindowHeight = dipToPx(config.screenHeightDp);
                    }
                }
            }
            //1.开始测量
            windowSizeMayChange |= measureHierarchy(host, lp, res,
                    desiredWindowWidth, desiredWindowHeight);
        }
        ...省略代码
        final boolean didLayout = layoutRequested && (!mStopped || mReportNextDraw);
        boolean triggerGlobalLayoutListener = didLayout
                || mAttachInfo.mRecomputeGlobalAttributes;
        if (didLayout) {
            //2 开始layout
            performLayout(lp, mWidth, mHeight);
            ... 省略代码
        }
        ... 省略代码
        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();
            }
        //3. 开始draw
            performDraw();
        } 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;
    }

 private void performMeasure(int childWidthMeasureSpec, int childHeightMeasureSpec) {
        Trace.traceBegin(Trace.TRACE_TAG_VIEW, "measure");
        try {
            mView.measure(childWidthMeasureSpec, childHeightMeasureSpec);
        } finally {
            Trace.traceEnd(Trace.TRACE_TAG_VIEW);
        }
    }
    private void performLayout(WindowManager.LayoutParams lp, int desiredWindowWidth,
            int desiredWindowHeight) {
       ...省略代码
            host.layout(0, 0, host.getMeasuredWidth(), host.getMeasuredHeight());
         ...省略代码
        mInLayout = false;
    }

protected void measureChildWithMargins(View child,
            int parentWidthMeasureSpec, int widthUsed,
            int parentHeightMeasureSpec, int heightUsed) {
        final MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();
        final int childWidthMeasureSpec = getChildMeasureSpec(parentWidthMeasureSpec,
                mPaddingLeft + mPaddingRight + lp.leftMargin + lp.rightMargin
                        + widthUsed, lp.width);
        final int childHeightMeasureSpec = getChildMeasureSpec(parentHeightMeasureSpec,
                mPaddingTop + mPaddingBottom + lp.topMargin + lp.bottomMargin
                        + heightUsed, lp.height);
        child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
    }

public static int getChildMeasureSpec(int spec, int padding, int childDimension) {
        int specMode = MeasureSpec.getMode(spec);
        int specSize = MeasureSpec.getSize(spec);
        int size = Math.max(0, specSize - padding);
        int resultSize = 0;
        int resultMode = 0;
        switch (specMode) {
        // Parent has imposed an exact size on us
        case MeasureSpec.EXACTLY:
            if (childDimension >= 0) {
                resultSize = childDimension;
                resultMode = MeasureSpec.EXACTLY;
            } else if (childDimension == LayoutParams.MATCH_PARENT) {
                // Child wants to be our size. So be it.
                resultSize = size;
                resultMode = MeasureSpec.EXACTLY;
            } else if (childDimension == LayoutParams.WRAP_CONTENT) {
                // Child wants to determine its own size. It can't be
                // bigger than us.
                resultSize = size;
                resultMode = MeasureSpec.AT_MOST;
            }
            break;
        // Parent has imposed a maximum size on us
        case MeasureSpec.AT_MOST:
            if (childDimension >= 0) {
                // Child wants a specific size... so be it
                resultSize = childDimension;
                resultMode = MeasureSpec.EXACTLY;
            } else if (childDimension == LayoutParams.MATCH_PARENT) {
                // Child wants to be our size, but our size is not fixed.
                // Constrain child to not be bigger than us.
                resultSize = size;
                resultMode = MeasureSpec.AT_MOST;
            } else if (childDimension == LayoutParams.WRAP_CONTENT) {
                // Child wants to determine its own size. It can't be
                // bigger than us.
                resultSize = size;
                resultMode = MeasureSpec.AT_MOST;
            }
            break;
        // Parent asked to see how big we want to be
        case MeasureSpec.UNSPECIFIED:
            if (childDimension >= 0) {
                // Child wants a specific size... let him have it
                resultSize = childDimension;
                resultMode = MeasureSpec.EXACTLY;
            } else if (childDimension == LayoutParams.MATCH_PARENT) {
                // Child wants to be our size... find out how big it should
                // be
                resultSize = View.sUseZeroUnspecifiedMeasureSpec ? 0 : size;
                resultMode = MeasureSpec.UNSPECIFIED;
            } else if (childDimension == LayoutParams.WRAP_CONTENT) {
                // Child wants to determine its own size.... find out how
                // big it should be
                resultSize = View.sUseZeroUnspecifiedMeasureSpec ? 0 : size;
                resultMode = MeasureSpec.UNSPECIFIED;
            }
            break;
        }
        //noinspection ResourceType
        return MeasureSpec.makeMeasureSpec(resultSize, resultMode);
    }