Android 事件系列-2 ViewGroup 中的事件分发

public class MyLinearLayout extends LinearLayout {

    final String TAG = "MyLinearLayout";

    public MyLinearLayout(Context context) {
        super(context);
    }

    public MyLinearLayout(Context context,  AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        Log.e(TAG,"dispatchTouchEvent="+ev.getAction());
        return super.dispatchTouchEvent(ev);
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        Log.e(TAG,"onInterceptTouchEvent="+ev.getAction());
        return super.onInterceptTouchEvent(ev);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        Log.e(TAG,"onTouchEvent="+event.getAction());
        return super.onTouchEvent(event);
    }
}

public class MyButton extends android.support.v7.widget.AppCompatButton {
    static final String TAG = "MyButton";
    public MyButton(Context context) {
        super(context);
    }

    public MyButton(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    public boolean dispatchTouchEvent(MotionEvent event) {
        Log.e(TAG,"dispatchTouchEvent="+event.getAction());
        return super.dispatchTouchEvent(event);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        Log.e(TAG,"onTouchEvent="+event.getAction());
        return super.onTouchEvent(event);
    }
}

public class MainActivity extends AppCompatActivity implements View.OnClickListener, View.OnTouchListener {

    private static final String TAG = "EventDemo";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        findViewById(R.id.button).setOnTouchListener(this);
        findViewById(R.id.button).setOnClickListener(this);
        findViewById(R.id.linearlayout).setOnTouchListener(this);
        findViewById(R.id.linearlayout).setOnClickListener(this);

    }

    @Override
    public void onClick(View v) {
        Log.e(TAG,"onClick=="+v.toString());
    }

    @Override
    public boolean onTouch(View v, MotionEvent event) {
        Log.e(TAG,"onTouch==="+event.getAction()+"===v==="+v.toString());
        return false;
    }
}

    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        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.
        if (ev.isTargetAccessibilityFocus() && isAccessibilityFocusedViewOrHost()) {
            ev.setTargetAccessibilityFocus(false);
        }

        boolean handled = false;
        if (onFilterTouchEventForSecurity(ev)) {
            final int action = ev.getAction();
            final int actionMasked = action & MotionEvent.ACTION_MASK;

            // Handle an initial down.
            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);
                resetTouchState();
            }

            // Check for interception.
            final boolean intercepted;
            if (actionMasked == MotionEvent.ACTION_DOWN
                    || mFirstTouchTarget != null) {
                final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
                if (!disallowIntercept) {
                    intercepted = onInterceptTouchEvent(ev);
                    ev.setAction(action); // restore action in case it was changed
                } else {
                    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.
            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;
            TouchTarget newTouchTarget = null;
            //定义一个变量 记录是否已经完成派发，由于确定派发目标使用了子控件的 dispatchTouchEvent，因此确定派发目标的时候实际上已经完成派发，这种情况下该变量将被设置为 true
            boolean alreadyDispatchedToNewTouchTarget = false;
            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.
                View childWithAccessibilityFocus = ev.isTargetAccessibilityFocus()
                        ? findChildWithAccessibilityFocus() : null;

                if (actionMasked == MotionEvent.ACTION_DOWN
                        || (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)
                        || actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
                    final int actionIndex = ev.getActionIndex(); // always 0 for down
                    //通过索引号获得触控点 id，当找到派发目标后，会将这个 idBitsToAssign 和目标 View 一起生成一个 TouchTarget
                    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);

                    final int childrenCount = mChildrenCount;
                    if (newTouchTarget == null && childrenCount != 0) {
                    //触摸事件是基于位置进行派发目标的查找，要先获取事件的坐标
                        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.
                        final ArrayList<View> preorderedList = buildTouchDispatchChildList();
                        final boolean customOrder = preorderedList == null
                                && isChildrenDrawingOrderEnabled();
                        final View[] children = mChildren;
                        for (int i = childrenCount - 1; i >= 0; i--) {
                            final int childIndex = getAndVerifyPreorderedIndex(
                                    childrenCount, i, customOrder);
                            final View child = getAndVerifyPreorderedView(
                                    preorderedList, children, childIndex);

                            // If there is a view that has accessibility focus we want it
                            // to get the event first and if not handled we will perform a
                            // normal dispatch. We may do a double iteration but this is
                            // safer given the timeframe.
                            if (childWithAccessibilityFocus != null) {
                                if (childWithAccessibilityFocus != child) {
                                    continue;
                                }
                                childWithAccessibilityFocus = null;
                                i = childrenCount - 1;
                            }
//检查点击事件是否在控件的坐标范围内，如果不在跳过 查找下一个控件
                            if (!canViewReceivePointerEvents(child)
                                    || !isTransformedTouchPointInView(x, y, child, null)) {
                                ev.setTargetAccessibilityFocus(false);
                                continue;
                            }

//查找当前控件是否已经在 mFirstTouchTarget 链表中，如果在表明该控件已经在接收一组事件，ViewGroup 会默认该控件对本组事件也感兴趣，将本组事件的目标设置为当前控件，并终止派发目标的查找。
                            newTouchTarget = getTouchTarget(child);
                            if (newTouchTarget != null) {
                                // Child is already receiving touch within its bounds.
                                // Give it the new pointer in addition to the ones it is handling.
                                newTouchTarget.pointerIdBits |= idBitsToAssign;
                                break;
                            }

                            resetCancelNextUpFlag(child);
                            // 使用 dispatchTransformedTouchEvent 尝试将事件派发给当前子控件，
                            if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
                                // Child wants to receive touch within its bounds.
                                mLastTouchDownTime = ev.getDownTime();
                                if (preorderedList != null) {
                                    // childIndex points into presorted list, find original index
                                    for (int j = 0; j < childrenCount; j++) {
                                        if (children[childIndex] == mChildren[j]) {
                                            mLastTouchDownIndex = j;
                                            break;
                                        }
                                    }
                                } else {
                                    mLastTouchDownIndex = childIndex;
                                }
                                mLastTouchDownX = ev.getX();
                                mLastTouchDownY = ev.getY();
                                //该子控件决定接受本组事件，将子控件添加到目标链表中。
                                newTouchTarget = addTouchTarget(child, idBitsToAssign);
                                alreadyDispatchedToNewTouchTarget = true;
                                break;
                            }

                            // The accessibility focus didn't handle the event, so clear
                            // the flag and do a normal dispatch to all children.
                            ev.setTargetAccessibilityFocus(false);
                        }
                        if (preorderedList != null) preorderedList.clear();
                    }

                    if (newTouchTarget == null && mFirstTouchTarget != null) {
                        // Did not find a child to receive the event.
                        // Assign the pointer to the least recently added target.
                        newTouchTarget = mFirstTouchTarget;
                        while (newTouchTarget.next != null) {
                            newTouchTarget = newTouchTarget.next;
                        }
                        newTouchTarget.pointerIdBits |= idBitsToAssign;
                    }
                }
            }

            // Dispatch to touch targets.
            if (mFirstTouchTarget == null) {
                // No touch targets so treat this as an ordinary view.
                //没有找到子控件接受事件，自己处理事件
                handled = dispatchTransformedTouchEvent(ev, canceled, null,
                        TouchTarget.ALL_POINTER_IDS);
            } else {
                // Dispatch to touch targets, excluding the new touch target if we already
                // dispatched to it.  Cancel touch targets if necessary.
                TouchTarget predecessor = null;
                TouchTarget target = mFirstTouchTarget;
                while (target != null) {
                    final TouchTarget next = target.next;
                    if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
                    //如果 touchTarget 是新确定的 touchTarget，在确定目标的过程中已经将事件分发出去，不需要再派发。
                        handled = true;
                    } else {
                        final boolean cancelChild = resetCancelNextUpFlag(target.child)
                                || intercepted;
                                
                                //将事件分发给子控件
                        if (dispatchTransformedTouchEvent(ev, cancelChild,
                                target.child, target.pointerIdBits)) {
                            handled = true;
                        }
                        if (cancelChild) {
                            if (predecessor == null) {
                                mFirstTouchTarget = next;
                            } else {
                                predecessor.next = next;
                            }
                            target.recycle();
                            target = next;
                            continue;
                        }
                    }
                    predecessor = target;
                    target = next;
                }
            }

            // Update list of touch targets for pointer up or cancel, if needed.
            if (canceled
                    || actionMasked == MotionEvent.ACTION_UP
                    || actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
                resetTouchState();
            } else if (split && actionMasked == MotionEvent.ACTION_POINTER_UP) {
                final int actionIndex = ev.getActionIndex();
                final int idBitsToRemove = 1 << ev.getPointerId(actionIndex);
                removePointersFromTouchTargets(idBitsToRemove);
            }
        }

        if (!handled && mInputEventConsistencyVerifier != null) {
            mInputEventConsistencyVerifier.onUnhandledEvent(ev, 1);
        }
        return handled;
    }

            // Handle an initial down.
            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);
                resetTouchState();
            }

    /**
     * Cancels and clears all touch targets.
     */
    private void cancelAndClearTouchTargets(MotionEvent event) {
        if (mFirstTouchTarget != null) {
            boolean syntheticEvent = false;
            if (event == null) {
                final long now = SystemClock.uptimeMillis();
                event = MotionEvent.obtain(now, now,
                        MotionEvent.ACTION_CANCEL, 0.0f, 0.0f, 0);
                event.setSource(InputDevice.SOURCE_TOUCHSCREEN);
                syntheticEvent = true;
            }

            for (TouchTarget target = mFirstTouchTarget; target != null; target = target.next) {
                resetCancelNextUpFlag(target.child);
                dispatchTransformedTouchEvent(event, true, target.child, target.pointerIdBits);
            }
            clearTouchTargets();

            if (syntheticEvent) {
                event.recycle();
            }
        }
    }

 // Clean up after nested scrolls if this is the end of a gesture;
        // also cancel it if we tried an ACTION_DOWN but we didn't want the rest
        // of the gesture.
        if (actionMasked == MotionEvent.ACTION_UP ||
                actionMasked == MotionEvent.ACTION_CANCEL ||
                (actionMasked == MotionEvent.ACTION_DOWN && !result)) {
            stopNestedScroll();
        }

 /**
     * Clears all touch targets.
     */
    private void clearTouchTargets() {
        TouchTarget target = mFirstTouchTarget;
        if (target != null) {
            do {
                TouchTarget next = target.next;
                target.recycle();
                target = next;
            } while (target != null);
            mFirstTouchTarget = null;
        }
    }

  // Check for interception.
            final boolean intercepted;
            if (actionMasked == MotionEvent.ACTION_DOWN
                    || mFirstTouchTarget != null) {
                final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
                if (!disallowIntercept) {
                    intercepted = onInterceptTouchEvent(ev);
                    ev.setAction(action); // restore action in case it was changed
                } else {
                    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;
            }

   public boolean onInterceptTouchEvent(MotionEvent ev) {
        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;
    }

  // 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);
            }

final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0;

newTouchTarget = getTouchTarget(child);

 private TouchTarget getTouchTarget(@NonNull View child) {
        for (TouchTarget target = mFirstTouchTarget; target != null; target = target.next) {
            if (target.child == child) {
                return target;
            }
        }
        return null;
    }

if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
                                // Child wants to receive touch within its bounds.
                                mLastTouchDownTime = ev.getDownTime();
                                if (preorderedList != null) {
                                    // childIndex points into presorted list, find original index
                                    for (int j = 0; j < childrenCount; j++) {
                                        if (children[childIndex] == mChildren[j]) {
                                            mLastTouchDownIndex = j;
                                            break;
                                        }
                                    }
                                } else {
                                    mLastTouchDownIndex = childIndex;
                                }
                                mLastTouchDownX = ev.getX();
                                mLastTouchDownY = ev.getY();
                                newTouchTarget = addTouchTarget(child, idBitsToAssign);
                                alreadyDispatchedToNewTouchTarget = true;
                                break;
                            }

newTouchTarget = addTouchTarget(child, idBitsToAssign);

// Dispatch to touch targets.
            if (mFirstTouchTarget == null) {
                // No touch targets so treat this as an ordinary view.
                handled = dispatchTransformedTouchEvent(ev, canceled, null,
                        TouchTarget.ALL_POINTER_IDS);
            } else {
                // Dispatch to touch targets, excluding the new touch target if we already
                // dispatched to it.  Cancel touch targets if necessary.
                TouchTarget predecessor = null;
                TouchTarget target = mFirstTouchTarget;
                while (target != null) {
                    final TouchTarget next = target.next;
                    if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
                        handled = true;
                    } else {
                        final boolean cancelChild = resetCancelNextUpFlag(target.child)
                                || intercepted;
                        if (dispatchTransformedTouchEvent(ev, cancelChild,
                                target.child, target.pointerIdBits)) {
                            handled = true;
                        }
                        if (cancelChild) {
                            if (predecessor == null) {
                                mFirstTouchTarget = next;
                            } else {
                                predecessor.next = next;
                            }
                            target.recycle();
                            target = next;
                            continue;
                        }
                    }
                    predecessor = target;
                    target = next;
                }
            }