// 此处判定 , 是否拦截 
    // 假定不取消 , 也不拦截 
    // canceled 和 intercepted 二者都是 false , 才不能拦截 ; 
            if (!canceled && !intercepted) {

View childWithAccessibilityFocus = ev.isTargetAccessibilityFocus()
                        ? findChildWithAccessibilityFocus() : null;

// 判断是否是按下操作 
                if (actionMasked == MotionEvent.ACTION_DOWN
                        || (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)
                        || actionMasked == MotionEvent.ACTION_HOVER_MOVE) {

// 获取触摸索引值 
                    final int actionIndex = ev.getActionIndex(); // always 0 for down

@UiThread
public abstract class ViewGroup extends View implements ViewParent, ViewManager {
    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
  ...
    // 此处判定 , 是否拦截 
    // 假定不取消 , 也不拦截 
    // canceled 和 intercepted 二者都是 false , 才不能拦截 ; 
            if (!canceled && !intercepted) {
                // If the event is targeting accessibility focus we give it to the
                // view that has accessibility focus and if it does not handle it
                // we clear the flag and dispatch the event to all children as usual.
                // We are looking up the accessibility focused host to avoid keeping
                // state since these events are very rare.
                // 无障碍 辅助功能 
                View childWithAccessibilityFocus = ev.isTargetAccessibilityFocus()
                        ? findChildWithAccessibilityFocus() : null;
    // 判断是否是按下操作 
                if (actionMasked == MotionEvent.ACTION_DOWN
                        || (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)
                        || actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
                    // 获取触摸索引值 
                    final int actionIndex = ev.getActionIndex(); // always 0 for down
                    final int idBitsToAssign = split ? 1 << ev.getPointerId(actionIndex)
                            : TouchTarget.ALL_POINTER_IDS;
                    // Clean up earlier touch targets for this pointer id in case they
                    // have become out of sync.
                    removePointersFromTouchTargets(idBitsToAssign);
  ...
    }
}

// 计算 ViewGroup 父容器下面有多少个子 View 组件 ; 
                    final int childrenCount = mChildrenCount;

// 获取单个手指的 x,y 坐标 
                        final float x = ev.getX(actionIndex);
                        final float y = ev.getY(actionIndex);

// TouchTarget newTouchTarget = null; 在上面声明为空 , 此处肯定为 null ; 
                    // childrenCount 子组件个数不为 0 
                    // 如果子组件个数为 0 , 则不走下一段代码 , 如果子组件个数大于 0 , 则执行下一段代码 ; 
                    // 说明下面的代码块中处理的是 ViewGroup 中子组件的事件分发功能 ; 
                    if (newTouchTarget == null && childrenCount != 0) {
                        // 获取单个手指的 x,y 坐标 
                        final float x = ev.getX(actionIndex);
                        final float y = ev.getY(actionIndex);
                        // Find a child that can receive the event.
                        // Scan children from front to back.
                        // 子组件排序 , 按照 Z 轴排列的层级 , 从上到下进行排序 , 
                        // 控件会相互重叠 , Z 轴的排列次序上 , 
                        // 顶层的组件优先获取到触摸事件 
                        final ArrayList<View> preorderedList = buildTouchDispatchChildList();

// 下面的组件排序的核心逻辑 
        // 获取当前所有组件的子组件的 Z 轴的深度 
        // 按照 Z 轴深度进行排序 
        // Z 轴方向上 , 对于事件传递 , 上面的组件优先级高于被覆盖的下面的组件优先级
        for (int i = 0; i < childrenCount; i++) {
            // add next child (in child order) to end of list
            final int childIndex = getAndVerifyPreorderedIndex(childrenCount, i, customOrder);
            final View nextChild = mChildren[childIndex];
            final float currentZ = nextChild.getZ();
            // insert ahead of any Views with greater Z
            // 计算当前遍历的组件应该被放到的索引位置
            int insertIndex = i;
            while (insertIndex > 0 && mPreSortedChildren.get(insertIndex - 1).getZ() > currentZ) {
                insertIndex--;
            }
            // 将当前遍历的组件插入到指定索引位置上 
            mPreSortedChildren.add(insertIndex, nextChild);
        }

@UiThread
public abstract class ViewGroup extends View implements ViewParent, ViewManager {
    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
  ...
        // 计算 ViewGroup 父容器下面有多少个子 View 组件 ; 
                    final int childrenCount = mChildrenCount;
                    // TouchTarget newTouchTarget = null; 在上面声明为空 , 此处肯定为 null ; 
                    // childrenCount 子组件个数不为 0 
                    // 如果子组件个数为 0 , 则不走下一段代码 , 如果子组件个数大于 0 , 则执行下一段代码 ; 
                    // 说明下面的代码块中处理的是 ViewGroup 中子组件的事件分发功能 ; 
                    if (newTouchTarget == null && childrenCount != 0) {
                        // 获取单个手指的 x,y 坐标 
                        final float x = ev.getX(actionIndex);
                        final float y = ev.getY(actionIndex);
                        // Find a child that can receive the event.
                        // Scan children from front to back.
                        // 子组件排序 , 按照 Z 轴排列的层级 , 从上到下进行排序 , 
                        // 控件会相互重叠 , Z 轴的排列次序上 , 
                        // 顶层的组件优先获取到触摸事件 
                        final ArrayList<View> preorderedList = buildTouchDispatchChildList();
                        final boolean customOrder = preorderedList == null
                                && isChildrenDrawingOrderEnabled();
                        final View[] children = mChildren;
  ...
    }
    /**
     * Provide custom ordering of views in which the touch will be dispatched.
     * 按照事件传递的顺序进行组件排序 
     *
     * This is called within a tight loop, so you are not allowed to allocate objects, including
     * the return array. Instead, you should return a pre-allocated list that will be cleared
     * after the dispatch is finished.
     * @hide
     */
    public ArrayList<View> buildTouchDispatchChildList() {
        return buildOrderedChildList();
    }
    /**
     * Populates (and returns) mPreSortedChildren with a pre-ordered list of the View's children,
     * sorted first by Z, then by child drawing order (if applicable). This list must be cleared
     * after use to avoid leaking child Views.
     *
     * Uses a stable, insertion sort which is commonly O(n) for ViewGroups with very few elevated
     * children.
     */
    ArrayList<View> buildOrderedChildList() {
        final int childrenCount = mChildrenCount;
        if (childrenCount <= 1 || !hasChildWithZ()) return null;
        if (mPreSortedChildren == null) {
            mPreSortedChildren = new ArrayList<>(childrenCount);
        } else {
            // callers should clear, so clear shouldn't be necessary, but for safety...
            mPreSortedChildren.clear();
            mPreSortedChildren.ensureCapacity(childrenCount);
        }
        final boolean customOrder = isChildrenDrawingOrderEnabled();
        // 下面的组件排序的核心逻辑 
        // 获取当前所有组件的子组件的 Z 轴的深度 
        // 按照 Z 轴深度进行排序 
        // Z 轴方向上 , 对于事件传递 , 上面的组件优先级高于被覆盖的下面的组件优先级
        for (int i = 0; i < childrenCount; i++) {
            // add next child (in child order) to end of list
            final int childIndex = getAndVerifyPreorderedIndex(childrenCount, i, customOrder);
            final View nextChild = mChildren[childIndex];
            final float currentZ = nextChild.getZ();
            // insert ahead of any Views with greater Z
            // 计算当前遍历的组件应该被放到的索引位置
            int insertIndex = i;
            while (insertIndex > 0 && mPreSortedChildren.get(insertIndex - 1).getZ() > currentZ) {
                insertIndex--;
            }
            // 将当前遍历的组件插入到指定索引位置上 
            mPreSortedChildren.add(insertIndex, nextChild);
        }
        return mPreSortedChildren;
    }
    // 获取排序后的子组件的索引值
    private int getAndVerifyPreorderedIndex(int childrenCount, int i, boolean customOrder) {
        final int childIndex;
        if (customOrder) {
            final int childIndex1 = getChildDrawingOrder(childrenCount, i);
            if (childIndex1 >= childrenCount) {
                throw new IndexOutOfBoundsException("getChildDrawingOrder() "
                        + "returned invalid index " + childIndex1
                        + " (child count is " + childrenCount + ")");
            }
            childIndex = childIndex1;
        } else {
            childIndex = i;
        }
        return childIndex;
    }
}

@UiThread
public abstract class ViewGroup extends View implements ViewParent, ViewManager {
    // First touch target in the linked list of touch targets.
    private TouchTarget mFirstTouchTarget;
    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        // 辅助功能 , 残疾人相关辅助 , 跨进程调用 无障碍 功能
        if (mInputEventConsistencyVerifier != null) {
            mInputEventConsistencyVerifier.onTouchEvent(ev, 1);
        }
        // If the event targets the accessibility focused view and this is it, start
        // normal event dispatch. Maybe a descendant is what will handle the click.
        // 判断产生事件的目标组件是可访问性的 , 那么按照普通的事件分发进行处理 ; 
        // 可能由其子类处理点击事件 ; 
        // 判断当前是否正在使用 无障碍 相关功能产生事件 
        if (ev.isTargetAccessibilityFocus() && isAccessibilityFocusedViewOrHost()) {
            ev.setTargetAccessibilityFocus(false);
        }
  // 是否按下操作 , 最终的对外返回结果 , 该方法的最终返回值 
        boolean handled = false;
        if (onFilterTouchEventForSecurity(ev)) {
            final int action = ev.getAction();
            final int actionMasked = action & MotionEvent.ACTION_MASK;
            // Handle an initial down.
            // 判断是否是第一次按下 , 如果是第一次按下 , 则执行下面的业务逻辑 
            if (actionMasked == MotionEvent.ACTION_DOWN) {
                // Throw away all previous state when starting a new touch gesture.
                // The framework may have dropped the up or cancel event for the previous gesture
                // due to an app switch, ANR, or some other state change.
                cancelAndClearTouchTargets(ev);
                // 如果是第一次按下 , 那么重置触摸状态 
                resetTouchState();
            }
            // Check for interception.
            // 判定是否拦截 
            // 用于多点触控按下操作的判定 
            final boolean intercepted;
            if (actionMasked == MotionEvent.ACTION_DOWN
                    || mFirstTouchTarget != null) {
                // 判断是否需要拦截 , 可以使用 requestDisallowInterceptTouchEvent 方法进行设置
                final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
                if (!disallowIntercept) {
                    // 进行事件拦截 
                    // 该 onInterceptTouchEvent 方法只返回是否进行事件拦截 , 返回一个布尔值 , 没有进行具体的事件拦截 
                    // 是否进行拦截 , 赋值给了 intercepted 局部变量 
                    // 该值决定是否进行拦截 
                    intercepted = onInterceptTouchEvent(ev);
                    ev.setAction(action); // restore action in case it was changed
                } else {
                    // 不进行事件拦截 
                    intercepted = false;
                }
            } else {
                // There are no touch targets and this action is not an initial down
                // so this view group continues to intercept touches.
                intercepted = true;
            }
            // If intercepted, start normal event dispatch. Also if there is already
            // a view that is handling the gesture, do normal event dispatch.
            if (intercepted || mFirstTouchTarget != null) {
                ev.setTargetAccessibilityFocus(false);
            }
            // Check for cancelation.
            // 检查是否取消操作 , 手指是否移除了组件便捷 ; 
            // 一般情况默认该值是 false ; 
            final boolean canceled = resetCancelNextUpFlag(this)
                    || actionMasked == MotionEvent.ACTION_CANCEL;
            // Update list of touch targets for pointer down, if needed.
            final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0;
            // 注意此处 newTouchTarget 为空 
            TouchTarget newTouchTarget = null;
            boolean alreadyDispatchedToNewTouchTarget = false;
    // 此处判定 , 是否拦截 
    // 假定不取消 , 也不拦截 
    // canceled 和 intercepted 二者都是 false , 才不能拦截 ; 
            if (!canceled && !intercepted) {
                // If the event is targeting accessibility focus we give it to the
                // view that has accessibility focus and if it does not handle it
                // we clear the flag and dispatch the event to all children as usual.
                // We are looking up the accessibility focused host to avoid keeping
                // state since these events are very rare.
                // 无障碍 辅助功能 
                View childWithAccessibilityFocus = ev.isTargetAccessibilityFocus()
                        ? findChildWithAccessibilityFocus() : null;
    // 判断是否是按下操作 
                if (actionMasked == MotionEvent.ACTION_DOWN
                        || (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)
                        || actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
                    // 获取触摸索引值 
                    final int actionIndex = ev.getActionIndex(); // always 0 for down
                    final int idBitsToAssign = split ? 1 << ev.getPointerId(actionIndex)
                            : TouchTarget.ALL_POINTER_IDS;
                    // Clean up earlier touch targets for this pointer id in case they
                    // have become out of sync.
                    removePointersFromTouchTargets(idBitsToAssign);
        // 计算 ViewGroup 父容器下面有多少个子 View 组件 ; 
                    final int childrenCount = mChildrenCount;
                    // TouchTarget newTouchTarget = null; 在上面声明为空 , 此处肯定为 null ; 
                    // childrenCount 子组件个数不为 0 
                    // 如果子组件个数为 0 , 则不走下一段代码 , 如果子组件个数大于 0 , 则执行下一段代码 ; 
                    // 说明下面的代码块中处理的是 ViewGroup 中子组件的事件分发功能 ; 
                    if (newTouchTarget == null && childrenCount != 0) {
                        // 获取单个手指的 x,y 坐标 
                        final float x = ev.getX(actionIndex);
                        final float y = ev.getY(actionIndex);
                        // Find a child that can receive the event.
                        // Scan children from front to back.
                        // 子组件排序 , 按照 Z 轴排列的层级 , 从上到下进行排序 , 
                        // 控件会相互重叠 , Z 轴的排列次序上 , 
                        // 顶层的组件优先获取到触摸事件 
                        final ArrayList<View> preorderedList = buildTouchDispatchChildList();
                        final boolean customOrder = preorderedList == null
                                && isChildrenDrawingOrderEnabled();
                        final View[] children = mChildren;
  ... 
        return handled;
    }
    @Override
    public void requestDisallowInterceptTouchEvent(boolean disallowIntercept) {
  // disallowIntercept 存在一个默认值 , 如果值为默认值 , 直接退出 
        if (disallowIntercept == ((mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0)) {
            // We're already in this state, assume our ancestors are too
            return;
        }
  // 如果不是默认值 , 则进行相应更改 
  // 最终的值影响 mGroupFlags 是 true 还是 false 
        if (disallowIntercept) {
            mGroupFlags |= FLAG_DISALLOW_INTERCEPT;
        } else {
            mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT;
        }
        // Pass it up to our parent
        if (mParent != null) {
            mParent.requestDisallowInterceptTouchEvent(disallowIntercept);
        }
    }
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        // 该方法只返回是否进行事件拦截 , 返回一个布尔值 , 没有进行具体的事件拦截 
        if (ev.isFromSource(InputDevice.SOURCE_MOUSE)
                && ev.getAction() == MotionEvent.ACTION_DOWN
                && ev.isButtonPressed(MotionEvent.BUTTON_PRIMARY)
                && isOnScrollbarThumb(ev.getX(), ev.getY())) {
            return true;
        }
        return false;
    }
    /**
     * Provide custom ordering of views in which the touch will be dispatched.
     * 按照事件传递的顺序进行组件排序 
     *
     * This is called within a tight loop, so you are not allowed to allocate objects, including
     * the return array. Instead, you should return a pre-allocated list that will be cleared
     * after the dispatch is finished.
     * @hide
     */
    public ArrayList<View> buildTouchDispatchChildList() {
        return buildOrderedChildList();
    }
    /**
     * Populates (and returns) mPreSortedChildren with a pre-ordered list of the View's children,
     * sorted first by Z, then by child drawing order (if applicable). This list must be cleared
     * after use to avoid leaking child Views.
     *
     * Uses a stable, insertion sort which is commonly O(n) for ViewGroups with very few elevated
     * children.
     */
    ArrayList<View> buildOrderedChildList() {
        final int childrenCount = mChildrenCount;
        if (childrenCount <= 1 || !hasChildWithZ()) return null;
        if (mPreSortedChildren == null) {
            mPreSortedChildren = new ArrayList<>(childrenCount);
        } else {
            // callers should clear, so clear shouldn't be necessary, but for safety...
            mPreSortedChildren.clear();
            mPreSortedChildren.ensureCapacity(childrenCount);
        }
        final boolean customOrder = isChildrenDrawingOrderEnabled();
        // 下面的组件排序的核心逻辑 
        // 获取当前所有组件的子组件的 Z 轴的深度 
        // 按照 Z 轴深度进行排序 
        // Z 轴方向上 , 对于事件传递 , 上面的组件优先级高于被覆盖的下面的组件优先级
        for (int i = 0; i < childrenCount; i++) {
            // add next child (in child order) to end of list
            final int childIndex = getAndVerifyPreorderedIndex(childrenCount, i, customOrder);
            final View nextChild = mChildren[childIndex];
            final float currentZ = nextChild.getZ();
            // insert ahead of any Views with greater Z
            // 计算当前遍历的组件应该被放到的索引位置
            int insertIndex = i;
            while (insertIndex > 0 && mPreSortedChildren.get(insertIndex - 1).getZ() > currentZ) {
                insertIndex--;
            }
            // 将当前遍历的组件插入到指定索引位置上 
            mPreSortedChildren.add(insertIndex, nextChild);
        }
        return mPreSortedChildren;
    }
}