每一個View都需要依賴於視窗來顯示，而View和視窗的關係則是放在View.AttachInfo中,關於View.AttachInfo的文章少，因為這個是View的內部類而且不是公共的，在應用層用的很少，只有在ViewRootImpl等類中才用到了，不過我覺得這個還是有點學習的必要，因此在這篇文章中就從原始碼入手學習下AttachInfo這個類。
    AttachInfo 看到這個類名，我們就知道，他是代表著繫結的資訊，View.AttachInfo 裡面的資訊，就是View和Window之間的資訊。每一個被新增到視窗上的View我們都會看到有一個AttachInfo，比如我們看DecorView和Window的繫結，可以在ViewRootImpl#perfromTraversals方法中看到：

 final View.AttachInfo attachInfo = mAttachInfo;

        final int viewVisibility = getHostVisibility();
        boolean viewVisibilityChanged = mViewVisibility != viewVisibility
                || mNewSurfaceNeeded;

        WindowManager.LayoutParams params = null;
        if (mWindowAttributesChanged) {
            mWindowAttributesChanged = false;
            surfaceChanged = true;
            params = lp;
        }
        CompatibilityInfo compatibilityInfo = mDisplayAdjustments.getCompatibilityInfo();
        if (compatibilityInfo.supportsScreen() == mLastInCompatMode) {
            params = lp;
            mFullRedrawNeeded = true;
            mLayoutRequested = true;
            if (mLastInCompatMode) {
                params.privateFlags &= ~WindowManager.LayoutParams.PRIVATE_FLAG_COMPATIBLE_WINDOW;
                mLastInCompatMode = false;
            } else {
                params.privateFlags |= WindowManager.LayoutParams.PRIVATE_FLAG_COMPATIBLE_WINDOW;
                mLastInCompatMode = true;
            }
        }

        mWindowAttributesChangesFlag = 0;

        Rect frame = mWinFrame;
        if (mFirst) {
            mFullRedrawNeeded = true;
            mLayoutRequested = true;

            if (lp.type == WindowManager.LayoutParams.TYPE_STATUS_BAR_PANEL
                    || lp.type == WindowManager.LayoutParams.TYPE_INPUT_METHOD) {
                // NOTE -- system code, won't try to do compat mode.
                Point size = new Point();
                mDisplay.getRealSize(size);
                desiredWindowWidth = size.x;
                desiredWindowHeight = size.y;
            } else {
                DisplayMetrics packageMetrics =
                    mView.getContext().getResources().getDisplayMetrics();
                desiredWindowWidth = packageMetrics.widthPixels;
                desiredWindowHeight = packageMetrics.heightPixels;
            }

            // For the very first time, tell the view hierarchy that it
            // is attached to the window.  Note that at this point the surface
            // object is not initialized to its backing store, but soon it
            // will be (assuming the window is visible).
            attachInfo.mSurface = mSurface;
            // We used to use the following condition to choose 32 bits drawing caches:
            // PixelFormat.hasAlpha(lp.format) || lp.format == PixelFormat.RGBX_8888
            // However, windows are now always 32 bits by default, so choose 32 bits
            attachInfo.mUse32BitDrawingCache = true;
            attachInfo.mHasWindowFocus = false;
            attachInfo.mWindowVisibility = viewVisibility;
            attachInfo.mRecomputeGlobalAttributes = false;
            viewVisibilityChanged = false;
            mLastConfiguration.setTo(host.getResources().getConfiguration());
            mLastSystemUiVisibility = mAttachInfo.mSystemUiVisibility;
            // Set the layout direction if it has not been set before (inherit is the default)
            if (mViewLayoutDirectionInitial == View.LAYOUT_DIRECTION_INHERIT) {
                host.setLayoutDirection(mLastConfiguration.getLayoutDirection());
            }
            host.dispatchAttachedToWindow(attachInfo, 0);
} 
 

AttachInfo 會通過View的diapatchAttachedTowWindow分發給View。如果是一個ViewGroup 那麼這個這個AttachInfo也會分發給所有子View，以引用的方式。 下面我們可以看下AttachInfo這個類，這個類是View的內部類，不是宣告為public的，所以只有view這個包中的類才用到。

static class AttachInfo {
        interface Callbacks {
            void playSoundEffect(int effectId);
            boolean performHapticFeedback(int effectId, boolean always);
        }

        /**
         * InvalidateInfo is used to post invalidate(int, int, int, int) messages
         * to a Handler. This class contains the target (View) to invalidate and
         * the coordinates of the dirty rectangle.
         *
         * For performance purposes, this class also implements a pool of up to
         * POOL_LIMIT objects that get reused. This reduces memory allocations
         * whenever possible.
         */
        static class InvalidateInfo {
            private static final int POOL_LIMIT = 10;

            private static final SynchronizedPool<InvalidateInfo> sPool =
                    new SynchronizedPool<InvalidateInfo>(POOL_LIMIT);

            View target;

            int left;
            int top;
            int right;
            int bottom;

            public static InvalidateInfo obtain() {
                InvalidateInfo instance = sPool.acquire();
                return (instance != null) ? instance : new InvalidateInfo();
            }

            public void recycle() {
                target = null;
                sPool.release(this);
            }
        }

        final IWindowSession mSession;

        final IWindow mWindow;

        final IBinder mWindowToken;

        final Display mDisplay;

        final Callbacks mRootCallbacks;

        HardwareCanvas mHardwareCanvas;

        IWindowId mIWindowId;
        WindowId mWindowId;

        /**
         * The top view of the hierarchy.
         */
        View mRootView;

        IBinder mPanelParentWindowToken;
        Surface mSurface;

        boolean mHardwareAccelerated;
        boolean mHardwareAccelerationRequested;
        HardwareRenderer mHardwareRenderer;

        boolean mScreenOn;

        /**
         * Scale factor used by the compatibility mode
         */
        float mApplicationScale;

        /**
         * Indicates whether the application is in compatibility mode
         */
        boolean mScalingRequired;

        /**
         * If set, ViewRootImpl doesn't use its lame animation for when the window resizes.
         */
        boolean mTurnOffWindowResizeAnim;

        /**
         * Left position of this view's window
         */
        int mWindowLeft;

        /**
         * Top position of this view's window
         */
        int mWindowTop;

        /**
         * Indicates whether views need to use 32-bit drawing caches
         */
        boolean mUse32BitDrawingCache;

        /**
         * For windows that are full-screen but using insets to layout inside
         * of the screen areas, these are the current insets to appear inside
         * the overscan area of the display.
         */
        final Rect mOverscanInsets = new Rect();

        /**
         * For windows that are full-screen but using insets to layout inside
         * of the screen decorations, these are the current insets for the
         * content of the window.
         */
        final Rect mContentInsets = new Rect();

        /**
         * For windows that are full-screen but using insets to layout inside
         * of the screen decorations, these are the current insets for the
         * actual visible parts of the window.
         */
        final Rect mVisibleInsets = new Rect();

        /**
         * The internal insets given by this window.  This value is
         * supplied by the client (through
         * {@link ViewTreeObserver.OnComputeInternalInsetsListener}) and will
         * be given to the window manager when changed to be used in laying
         * out windows behind it.
         */
        final ViewTreeObserver.InternalInsetsInfo mGivenInternalInsets
                = new ViewTreeObserver.InternalInsetsInfo();

        /**
         * Set to true when mGivenInternalInsets is non-empty.
         */
        boolean mHasNonEmptyGivenInternalInsets;

        /**
         * All views in the window's hierarchy that serve as scroll containers,
         * used to determine if the window can be resized or must be panned
         * to adjust for a soft input area.
         */
        final ArrayList<View> mScrollContainers = new ArrayList<View>();

        final KeyEvent.DispatcherState mKeyDispatchState
                = new KeyEvent.DispatcherState();

        /**
         * Indicates whether the view's window currently has the focus.
         */
        boolean mHasWindowFocus;

        /**
         * The current visibility of the window.
         */
        int mWindowVisibility;

        /**
         * Indicates the time at which drawing started to occur.
         */
        long mDrawingTime;

        /**
         * Indicates whether or not ignoring the DIRTY_MASK flags.
         */
        boolean mIgnoreDirtyState;

        /**
         * This flag tracks when the mIgnoreDirtyState flag is set during draw(),
         * to avoid clearing that flag prematurely.
         */
        boolean mSetIgnoreDirtyState = false;

        /**
         * Indicates whether the view's window is currently in touch mode.
         */
        boolean mInTouchMode;

        /**
         * Indicates that ViewAncestor should trigger a global layout change
         * the next time it performs a traversal
         */
        boolean mRecomputeGlobalAttributes;

        /**
         * Always report new attributes at next traversal.
         */
        boolean mForceReportNewAttributes;

        /**
         * Set during a traveral if any views want to keep the screen on.
         */
        boolean mKeepScreenOn;

        /**
         * Bitwise-or of all of the values that views have passed to setSystemUiVisibility().
         */
        int mSystemUiVisibility;

        /**
         * Hack to force certain system UI visibility flags to be cleared.
         */
        int mDisabledSystemUiVisibility;

        /**
         * Last global system UI visibility reported by the window manager.
         */
        int mGlobalSystemUiVisibility;

        /**
         * True if a view in this hierarchy has an OnSystemUiVisibilityChangeListener
         * attached.
         */
        boolean mHasSystemUiListeners;

        /**
         * Set if the window has requested to extend into the overscan region
         * via WindowManager.LayoutParams.FLAG_LAYOUT_IN_OVERSCAN.
         */
        boolean mOverscanRequested;

        /**
         * Set if the visibility of any views has changed.
         */
        boolean mViewVisibilityChanged;

        /**
         * Set to true if a view has been scrolled.
         */
        boolean mViewScrollChanged;

        /**
         * Global to the view hierarchy used as a temporary for dealing with
         * x/y points in the transparent region computations.
         */
        final int[] mTransparentLocation = new int[2];

        /**
         * Global to the view hierarchy used as a temporary for dealing with
         * x/y points in the ViewGroup.invalidateChild implementation.
         */
        final int[] mInvalidateChildLocation = new int[2];


        /**
         * Global to the view hierarchy used as a temporary for dealing with
         * x/y location when view is transformed.
         */
        final float[] mTmpTransformLocation = new float[2];

        /**
         * The view tree observer used to dispatch global events like
         * layout, pre-draw, touch mode change, etc.
         */
        final ViewTreeObserver mTreeObserver = new ViewTreeObserver();

        /**
         * A Canvas used by the view hierarchy to perform bitmap caching.
         */
        Canvas mCanvas;

        /**
         * The view root impl.
         */
        final ViewRootImpl mViewRootImpl;

        /**
         * A Handler supplied by a view's {@link android.view.ViewRootImpl}. This
         * handler can be used to pump events in the UI events queue.
         */
        final Handler mHandler;

        /**
         * Temporary for use in computing invalidate rectangles while
         * calling up the hierarchy.
         */
        final Rect mTmpInvalRect = new Rect();

        /**
         * Temporary for use in computing hit areas with transformed views
         */
        final RectF mTmpTransformRect = new RectF();

        /**
         * Temporary for use in transforming invalidation rect
         */
        final Matrix mTmpMatrix = new Matrix();

        /**
         * Temporary for use in transforming invalidation rect
         */
        final Transformation mTmpTransformation = new Transformation();

        /**
         * Temporary list for use in collecting focusable descendents of a view.
         */
        final ArrayList<View> mTempArrayList = new ArrayList<View>(24);

        /**
         * The id of the window for accessibility purposes.
         */
        int mAccessibilityWindowId = View.NO_ID;

        /**
         * Flags related to accessibility processing.
         *
         * @see AccessibilityNodeInfo#FLAG_INCLUDE_NOT_IMPORTANT_VIEWS
         * @see AccessibilityNodeInfo#FLAG_REPORT_VIEW_IDS
         */
        int mAccessibilityFetchFlags;

        /**
         * The drawable for highlighting accessibility focus.
         */
        Drawable mAccessibilityFocusDrawable;

        /**
         * Show where the margins, bounds and layout bounds are for each view.
         */
        boolean mDebugLayout = SystemProperties.getBoolean(DEBUG_LAYOUT_PROPERTY, false);

        /**
         * Point used to compute visible regions.
         */
        final Point mPoint = new Point();

        /**
         * Used to track which View originated a requestLayout() call, used when
         * requestLayout() is called during layout.
         */
        View mViewRequestingLayout;

        /**
         * Creates a new set of attachment information with the specified
         * events handler and thread.
         *
         * @param handler the events handler the view must use
         */
        AttachInfo(IWindowSession session, IWindow window, Display display,
                ViewRootImpl viewRootImpl, Handler handler, Callbacks effectPlayer) {
            mSession = session;
            mWindow = window;
            mWindowToken = window.asBinder();
            mDisplay = display;
            mViewRootImpl = viewRootImpl;
            mHandler = handler;
            mRootCallbacks = effectPlayer;
        }
    }
 

首先是聲明瞭回撥介面類：callBacks 這個類第一個是playSoundEffect ,這個用於播放按鍵聲音，引數是這個點選事件的型別，可以看SoundEffectConstants中的宣告，一般是SoundEffectConstants中幾個常量中的一個，在AttachInfo有一個CallBack物件 ：mRootCallBacks 這個的實現可以看ViewRootImpl類，ViewRootImpl中，我們可以看到：

  public void playSoundEffect(int effectId) {
        checkThread();

        if (mMediaDisabled) {
            return;
        }

        try {
            final AudioManager audioManager = getAudioManager();

            switch (effectId) {
                case SoundEffectConstants.CLICK:
                    audioManager.playSoundEffect(AudioManager.FX_KEY_CLICK);
                    return;
                case SoundEffectConstants.NAVIGATION_DOWN:
                    audioManager.playSoundEffect(AudioManager.FX_FOCUS_NAVIGATION_DOWN);
                    return;
                case SoundEffectConstants.NAVIGATION_LEFT:
                    audioManager.playSoundEffect(AudioManager.FX_FOCUS_NAVIGATION_LEFT);
                    return;
                case SoundEffectConstants.NAVIGATION_RIGHT:
                    audioManager.playSoundEffect(AudioManager.FX_FOCUS_NAVIGATION_RIGHT);
                    return;
                case SoundEffectConstants.NAVIGATION_UP:
                    audioManager.playSoundEffect(AudioManager.FX_FOCUS_NAVIGATION_UP);
                    return;
                default:
                    throw new IllegalArgumentException("unknown effect id " + effectId +
                            " not defined in " + SoundEffectConstants.class.getCanonicalName());
            }
        } catch (IllegalStateException e) {
            // Exception thrown by getAudioManager() when mView is null
            Log.e(TAG, "FATAL EXCEPTION when attempting to play sound effect: " + e);
            e.printStackTrace();
        }
    }

是的，這個就是控制AudioManager來播放我們系統的點選聲音，如果我們需要修改按鈕的點選聲音，就有如下幾個方法， 如果是修改Framework 那麼我們可以修改AudioManager的這個playSoundEffect方法，修改對應型別，也可以直接修改ViewRootImpl中這個方法（不建議），不過最後一個改動 基本上就是改動全域性，如果我們自定義控制元件想要觸發點選聲音不同呢？ 那麼我們在自定義的View上，重寫playSoundEffect方法就可以了。每一個View都有playSoundEffect方法，我們可以改動這個方法。 CallBack中還有一個方法： performHapticFeedback這個意思就是觸感反饋，引數可以看HapticFeedBack這個類，當用戶在系統開啟觸感反饋選項，我們View的 performHapticFeedback(int feedBackContants )這個方法，當然，如果我們呼叫 performHapticFeedback(int feedbackConstant, int flags) 的時候，把引數FLAG_IGNORE_GLOBAL_SETTING 就可以忽略全域性設定，而如果我們HapticFeedbackConstants.FLAG_IGNORE_VIEW_SETTING 就可以忽略我們在View裡面設定的android:hapticFeedbackEnabled  關於CallBack就講到這裡，接下來我們繼續往下看InvalidateInfo。 InvalidateInfo用於重新整理UI，當我們重新整理UI的時候，會生成一個新的 InvalidateInfo物件，然後根據這個來重新整理UI。這個比較簡單，就不詳細說了。 在AttachInfo中，還有其他的資訊，在這邊，我們可以拿到和Window相關的資訊：  

<span style="white-space:pre">	</span>final IWindowSession mSession;
<span style="white-space:pre">	</span>
        final IWindow mWindow;

        final IBinder mWindowToken;
        IBinder   mPanelParentWindowToken ；

一般來說，IWinodwSession是通過： WindowManagerGlobal.peekWindowSession() 或者是 WindowManagerGlobal.getWindowSession() 來獲取的 兩者一般來說是差不多的，就是peek返回的可能為空 get一般返回是不為空的。另外，IWindowSession 、IWindow 、mWindowToken 都是從 IWindowManager.Stub.asInterface( ServiceManager.getService("window")) 獲取到IWindowManager來獲取的。 相關的可以看前面的第10篇：Binder進階：系統服務中的Binder 以及ServiceManager的原始碼來看。 mPanelParentWindowToken 如果該視窗時子視窗，那麼該值就是父視窗的W物件，如果mWindowToken不為空，則說明沒有父視窗…嗯，和mWindowToken有點相對的意思。比如說Activity 的DecorView 的AttachInfo這個值就是null,而我們彈出了一個對話方塊，這個對話方塊的這個就不為null，因為這個對話方塊是有父視窗的。