android6.0 Activity（二） View创建过程

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每一个Activity组件都有一个关联的Window对象，用来描述一个应用程序窗口。每一个应用程序窗口内部又包含有一个View对象，用来描述应用程序窗口的视图。应用程序窗口视图是真正用来实现UI内容和布局的，也就是说，每一个Activity组件的UI内容和布局都是通过与其所关联的一个Window对象的内部的一个View对象来实现的。在本文中，我们就详细分析应用程序窗口视图的创建过程。

应用程序窗口内部所包含的视图对象的实际类型为DecorView。DecorView类继承了View类，是作为容器（ViewGroup）来使用的，它的实现如图

每一个Activity对象都有一个关联的ViewRootImpl对象，相当于是MVC模型中的Controller，它有以下职责：

1. 负责为应用程序窗口视图创建Surface。

2. 配合WindowManagerService来管理系统的应用程序窗口。

3. 负责管理、布局和渲染应用程序窗口视图的UI。

从前面Android应用程序启动过程源代码分析一文可以知道，Activity组件在启动的过程中，会调用ActivityThread类的成员函数handleLaunchActivity，用来创建以及首次激活Activity组件，因此，接下来我们就从这个函数开始，具体分析应用程序窗口的视图对象及其所关联的ViewRootImpl对象的创建过程,如图所示

setContentView中创建DecorView对象

一般在Activity的子类的onCreate方法中都会实现setContentView函数，我们来看Activity的这个函数：

    public void setContentView(View view) {        getWindow().setContentView(view);        initWindowDecorActionBar();    }

调用了PhoneWindow的setContentView函数，而在这个函数中调用了installDecor函数来创建DecorView对象

    @Override    public void setContentView(View view, ViewGroup.LayoutParams params) {        // Note: FEATURE_CONTENT_TRANSITIONS may be set in the process of installing the window        // decor, when theme attributes and the like are crystalized. Do not check the feature        // before this happens.        if (mContentParent == null) {            installDecor();        } else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) {            mContentParent.removeAllViews();        }        if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {            view.setLayoutParams(params);            final Scene newScene = new Scene(mContentParent, view);            transitionTo(newScene);        } else {            mContentParent.addView(view, params);        }        mContentParent.requestApplyInsets();        final Callback cb = getCallback();        if (cb != null && !isDestroyed()) {            cb.onContentChanged();        }    }

在installDecor函数中调用了generateDecor函数来创建DecorView

    private void installDecor() {        if (mDecor == null) {            mDecor = generateDecor();......

    protected DecorView generateDecor() {        return new DecorView(getContext(), -1);    }

创建ViewRootImpl对象

下面我们再从ActivityThread的handleResumeActivity函数看，先调用了performResumeActivity函数来查找这个Activity，后面主要调用了WindowManager的addView函数。

    final void handleResumeActivity(IBinder token,            boolean clearHide, boolean isForward, boolean reallyResume) {        // 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        ActivityClientRecord r = performResumeActivity(token, clearHide);        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;            if (!willBeVisible) {                try {                    willBeVisible = ActivityManagerNative.getDefault().willActivityBeVisible(                            a.getActivityToken());                } catch (RemoteException e) {                }            }            if (r.window == null && !a.mFinished && willBeVisible) {                r.window = r.activity.getWindow();                View decor = r.window.getDecorView();                decor.setVisibility(View.INVISIBLE);                ViewManager wm = a.getWindowManager();                WindowManager.LayoutParams l = r.window.getAttributes();                a.mDecor = decor;                l.type = WindowManager.LayoutParams.TYPE_BASE_APPLICATION;                l.softInputMode |= forwardBit;                if (a.mVisibleFromClient) {                    a.mWindowAdded = true;                    wm.addView(decor, l);                }

我们先来看performResumeActivity函数，这个函数主要是根据token来寻找ActivityClientRecord，然后调用了Activity的performResume方法。

    public final ActivityClientRecord performResumeActivity(IBinder token,            boolean clearHide) {        ActivityClientRecord r = mActivities.get(token);        if (localLOGV) Slog.v(TAG, "Performing resume of " + r                + " finished=" + r.activity.mFinished);        if (r != null && !r.activity.mFinished) {            if (clearHide) {                r.hideForNow = false;                r.activity.mStartedActivity = false;            }            try {                r.activity.onStateNotSaved();                r.activity.mFragments.noteStateNotSaved();                if (r.pendingIntents != null) {                    deliverNewIntents(r, r.pendingIntents);                    r.pendingIntents = null;                }                if (r.pendingResults != null) {                    deliverResults(r, r.pendingResults);                    r.pendingResults = null;                }                r.activity.performResume();                EventLog.writeEvent(LOG_AM_ON_RESUME_CALLED,                        UserHandle.myUserId(), r.activity.getComponentName().getClassName());                r.paused = false;                r.stopped = false;                r.state = null;                r.persistentState = null;            } 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;    }

后面有调用了Activity的getWindowManager方法获取WindowManager，之前的博客有分析过，这个WindowManager就是WindowManagerImpl对象。下面也就是调用了WindowManagerImpl的addView函数。

我们来看WindowManagerImpl的addView函数，其实就是调用了WindowManagerGlobal的addView函数

    @Override    public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {        applyDefaultToken(params);        mGlobal.addView(view, params, mDisplay, mParentWindow);    }

之前也分析过WindowManagerGlobal，它有3个重要的成员变量：

    private final ArrayList<View> mViews = new ArrayList<View>();//所有的DecorView对象    private final ArrayList<ViewRootImpl> mRoots = new ArrayList<ViewRootImpl>();//所有的ViewRootImpl对象    private final ArrayList<WindowManager.LayoutParams> mParams =//所有顶层View的layout参数            new ArrayList<WindowManager.LayoutParams>();

我们再来看WindowManagerGlobal的addView函数，这个函数先是查找是否已经在WindowManagerGlobal中已经有这个view，如果有的话就调用其ViewRootImpl的doDie函数中主要是调用WindowManagerGlobal函数去除这个ViewRootImpl对象，在这个主要是创建了ViewRootImpl，并且把DecorView，RootViewRootImpl，layout参数都保存起来了。然后调用了ViewRootImpl的setView函数。

    public void addView(View view, ViewGroup.LayoutParams params,            Display display, Window parentWindow) {        ......        int index = findViewLocked(view, false);//查找是否有该view，获取其index            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();//调用ViewRootImpl的doDie函数                } else {                    throw new IllegalStateException("View " + view                            + " has already been added to the window manager.");                }                // The previous removeView() had not completed executing. Now it has.            }        ......            root = new ViewRootImpl(view.getContext(), display);//新建ViewRootImpl对象            view.setLayoutParams(wparams);            mViews.add(view);//成员变量增加            mRoots.add(root);            mParams.add(wparams);        }        // do this last because it fires off messages to start doing things        try {            root.setView(view, wparams, panelParentView);//调用ViewRootImpl的setView函数        } catch (RuntimeException e) {            // BadTokenException or InvalidDisplayException, clean up.            synchronized (mLock) {                final int index = findViewLocked(view, false);                if (index >= 0) {                    removeViewLocked(index, true);                }            }            throw e;        }    }

我们再来看下ViewRootImpl的doDie函数中最后有下面一行代码：

WindowManagerGlobal.getInstance().doRemoveView(this);

而在WindowManagerGlobal中就是去除相关所有的保存。

    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 (HardwareRenderer.sTrimForeground && HardwareRenderer.isAvailable()) {            doTrimForeground();        }    }

ViewRootImpl的setView函数

下面我们再来看看ViewRootImpl的setView函数：

    public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {        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;                }                attrs = mWindowAttributes;                // 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);                    }                }                // Compute surface insets required to draw at specified Z value.                // TODO: Use real shadow insets for a constant max Z.                if (!attrs.hasManualSurfaceInsets) {                    final int surfaceInset = (int) Math.ceil(view.getZ() * 2);                    attrs.surfaceInsets.set(surfaceInset, surfaceInset, surfaceInset, surfaceInset);                }                CompatibilityInfo compatibilityInfo = mDisplayAdjustments.getCompatibilityInfo();                mTranslator = compatibilityInfo.getTranslator();                // If the application owns the surface, don't enable hardware acceleration                if (mSurfaceHolder == null) {                    enableHardwareAcceleration(attrs);                }                boolean restore = false;                if (mTranslator != null) {                    mSurface.setCompatibilityTranslator(mTranslator);                    restore = true;                    attrs.backup();                    mTranslator.translateWindowLayout(attrs);                }                if (DEBUG_LAYOUT) Log.d(TAG, "WindowLayout in setView:" + attrs);                if (!compatibilityInfo.supportsScreen()) {                    attrs.privateFlags |= WindowManager.LayoutParams.PRIVATE_FLAG_COMPATIBLE_WINDOW;                    mLastInCompatMode = true;                }                mSoftInputMode = attrs.softInputMode;                mWindowAttributesChanged = true;                mWindowAttributesChangesFlag = WindowManager.LayoutParams.EVERYTHING_CHANGED;                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; */                // Schedule the first layout -before- adding to the window                // manager, to make sure we do the relayout before receiving                // any other events from the system.                requestLayout();//绘制UI布局                if ((mWindowAttributes.inputFeatures                        & WindowManager.LayoutParams.INPUT_FEATURE_NO_INPUT_CHANNEL) == 0) {                    mInputChannel = new InputChannel();//创建按键通道                }                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 (mTranslator != null) {                    mTranslator.translateRectInScreenToAppWindow(mAttachInfo.mContentInsets);                }                mPendingOverscanInsets.set(0, 0, 0, 0);                mPendingContentInsets.set(mAttachInfo.mContentInsets);                mPendingStableInsets.set(mAttachInfo.mStableInsets);                mPendingVisibleInsets.set(0, 0, 0, 0);                if (DEBUG_LAYOUT) Log.v(TAG, "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 this type already exists");                        case WindowManagerGlobal.ADD_PERMISSION_DENIED:                            throw new WindowManager.BadTokenException(                                    "Unable to add window " + mWindow +                                    " -- permission denied for this window 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 is not valid");                    }                    throw new RuntimeException(                            "Unable to add window -- unknown error code " + res);                }                if (view instanceof RootViewSurfaceTaker) {                    mInputQueueCallback =                        ((RootViewSurfaceTaker)view).willYouTakeTheInputQueue();                }                if (mInputChannel != null) {                    if (mInputQueueCallback != null) {                        mInputQueue = new InputQueue();                        mInputQueueCallback.onInputQueueCreated(mInputQueue);                    }                    mInputEventReceiver = new WindowInputEventReceiver(mInputChannel,//创建按键应用层接受对象                            Looper.myLooper());                }                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();                mSyntheticInputStage = new SyntheticInputStage();//按键的一些流程类                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;            }        }    }

这个函数主要是调用了requestLayout函数来对应用窗口的UI布局，然后创建了InputChannel。调用ViewRoot类的静态成员变量sWindowSession所描述的一个类型为Session的Binder代理对象的成员函数add来请求WindowManagerService增加一个WindowState对象，以便可以用来描述当前正在处理的一个ViewRootImpl所关联的一个应用程序窗口。

最后创建了WindowInputEventReceiver应用层的按键接受，以及一些按键在应用层的流程的相关类。

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