View的事件分发

//事件流转协议
public interface Callback<T> {
    //传递某个事件/obj
    boolean dispatch(T obj);
}

public abstract class Stub<T> implements Callback<T> {

    private Callback next;

    //设置下游对象
    public void setNext(Callback Callback) {
        this.next = Callback;
    }

    @Override
    public boolean dispatch(T obj) {
        //如果自己不处理，就分发给下游处理
        boolean intercept = onIntercept(obj);
        if (!intercept && next != null) {
            //是否处理从链表下游返回
            intercept = next.dispatch(obj);
        }
        return intercept;
    }

    //自己是否处理
    abstract boolean onIntercept(T obj);

}

    public boolean dispatchTouchEvent(MotionEvent ev) {
        boolean consume = false;
        if (onInterceptTouchEvent(ev)) {
            consume = onTouchEvent(ev);
        } else {
            consume = child.dispatchTouchEvent(ev);
        }

        return consume;
    }

 1             当新事件序列到来时，进行一些重置操作
 2 　　　　　　　// Handle an initial down.
 3             if (actionMasked == MotionEvent.ACTION_DOWN) {
 4                 // Throw away all previous state when starting a new touch gesture.
 5                 // The framework may have dropped the up or cancel event for the previous gesture
 6                 // due to an app switch, ANR, or some other state change.
 7                 cancelAndClearTouchTargets(ev);
 8                 resetTouchState();
 9             }
10 
11 　　　　　　　判断是否进行事件的拦截
12             // Check for interception.
13             final boolean intercepted;
14             if (actionMasked == MotionEvent.ACTION_DOWN
15                     || mFirstTouchTarget != null) {
16                 final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
17                 if (!disallowIntercept) {
18                     intercepted = onInterceptTouchEvent(ev);
19                     ev.setAction(action); // restore action in case it was changed
20                 } else {
21                     intercepted = false;
22                 }
23             } else {
24                 // There are no touch targets and this action is not an initial down
25                 // so this view group continues to intercept touches.
26                 intercepted = true;
27             }

 public boolean onInterceptTouchEvent(MotionEvent ev) {
        if (ev.isFromSource(InputDevice.SOURCE_MOUSE)         //来自鼠标，一般不会有这个操作
                && ev.getAction() == MotionEvent.ACTION_DOWN
                && ev.isButtonPressed(MotionEvent.BUTTON_PRIMARY)
                && isOnScrollbarThumb(ev.getX(), ev.getY())) {
            return true;
        }
        return false;
    }

 1 public boolean dispatchTouchEvent(MotionEvent ev) {
 2     ......
 3      if (!canceled && !intercepted) {
 4          final View[] children = mChildren;
 5                         for (int i = childrenCount - 1; i >= 0; i--) {
 6                             final int childIndex = getAndVerifyPreorderedIndex(
 7                                     childrenCount, i, customOrder);
 8                             final View child = getAndVerifyPreorderedView(
 9                                     preorderedList, children, childIndex);
10 
11                             // If there is a view that has accessibility focus we want it
12                             // to get the event first and if not handled we will perform a
13                             // normal dispatch. We may do a double iteration but this is
14                             // safer given the timeframe.
15                             if (childWithAccessibilityFocus != null) {
16                                 if (childWithAccessibilityFocus != child) {
17                                     continue;
18                                 }
19                                 childWithAccessibilityFocus = null;
20                                 i = childrenCount - 1;
21                             }
22 
23                             if (!canViewReceivePointerEvents(child)
24                                     || !isTransformedTouchPointInView(x, y, child, null)) {
25                                 ev.setTargetAccessibilityFocus(false);
26                                 continue;
27                             }
28 
29                             newTouchTarget = getTouchTarget(child);
30                             if (newTouchTarget != null) {
31                                 // Child is already receiving touch within its bounds.
32                                 // Give it the new pointer in addition to the ones it is handling.
33                                 newTouchTarget.pointerIdBits |= idBitsToAssign;
34                                 break;
35                             }
36 
37                             resetCancelNextUpFlag(child);
38                             if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
39                                 // Child wants to receive touch within its bounds.
40                                 mLastTouchDownTime = ev.getDownTime();
41                                 if (preorderedList != null) {
42                                     // childIndex points into presorted list, find original index
43                                     for (int j = 0; j < childrenCount; j++) {
44                                         if (children[childIndex] == mChildren[j]) {
45                                             mLastTouchDownIndex = j;
46                                             break;
47                                         }
48                                     }
49                                 } else {
50                                     mLastTouchDownIndex = childIndex;
51                                 }
52                                 mLastTouchDownX = ev.getX();
53                                 mLastTouchDownY = ev.getY();
54                                 newTouchTarget = addTouchTarget(child, idBitsToAssign);  //完成对mFitstTouchEvent的赋值
55                                 alreadyDispatchedToNewTouchTarget = true;
56                                 break;
57                             }
58 
59 　　　　....
60     }
61 ......
62 }

 1  /**
 2      * Transforms a motion event into the coordinate space of a particular child view,
 3      * filters out irrelevant pointer ids, and overrides its action if necessary.
 4      * If child is null, assumes the MotionEvent will be sent to this ViewGroup instead.
 5      */
 6     private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,
 7             View child, int desiredPointerIdBits) {
 8 　　　　....
 9 
10         // Perform any necessary transformations and dispatch.
11         if (child == null) {
12             handled = super.dispatchTouchEvent(transformedEvent);
13         } else {
14             final float offsetX = mScrollX - child.mLeft;
15             final float offsetY = mScrollY - child.mTop;
16             transformedEvent.offsetLocation(offsetX, offsetY);
17             if (! child.hasIdentityMatrix()) {
18                 transformedEvent.transform(child.getInverseMatrix());
19             }
20             //此时child不为null,将事件分发给子元素
21             handled = child.dispatchTouchEvent(transformedEvent);   
22         }
23 　　　....
24 }

 @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
......
            // Dispatch to touch targets.
            if (mFirstTouchTarget == null) {  //没有子元素处理
                // No touch targets so treat this as an ordinary view.
                handled = dispatchTransformedTouchEvent(ev, canceled, null,
                        TouchTarget.ALL_POINTER_IDS);
            } 
....
}

 1 /**
 2      * Pass the touch screen motion event down to the target view, or this
 3      * view if it is the target.
 4      *
 5      * @param event The motion event to be dispatched.
 6      * @return True if the event was handled by the view, false otherwise.
 7      */
 8     public boolean dispatchTouchEvent(MotionEvent event) {
 9        ......
10 
11         if (onFilterTouchEventForSecurity(event)) {
12             if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {
13                 result = true;
14             }
15             //noinspection SimplifiableIfStatement
16             ListenerInfo li = mListenerInfo;
17             if (li != null && li.mOnTouchListener != null
18                     && (mViewFlags & ENABLED_MASK) == ENABLED
19                     && li.mOnTouchListener.onTouch(this, event)) {
20                 result = true;
21             }
22 
23             if (!result && onTouchEvent(event)) {
24                 result = true;
25             }
26         }
27 
28     ......
29         return result;
30     }

 1  public boolean onTouchEvent(MotionEvent event) {
 2         final float x = event.getX();
 3         final float y = event.getY();
 4         final int viewFlags = mViewFlags;
 5         final int action = event.getAction();
 6 
 7         final boolean clickable = ((viewFlags & CLICKABLE) == CLICKABLE
 8                 || (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)
 9                 || (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE;
10 
11         if ((viewFlags & ENABLED_MASK) == DISABLED) {
12             if (action == MotionEvent.ACTION_UP && (mPrivateFlags & PFLAG_PRESSED) != 0) {
13                 setPressed(false);
14             }
15             mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
16             // A disabled view that is clickable still consumes the touch
17             // events, it just doesn‘t respond to them.
18             return clickable;
19         }
20         if (mTouchDelegate != null) {
21             if (mTouchDelegate.onTouchEvent(event)) {
22                 return true;
23             }
24         }
25 
26         if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {
27             switch (action) {
28                 case MotionEvent.ACTION_UP:
29                     ....
30                     break;
31 
32                 case MotionEvent.ACTION_DOWN:
33                    ....
34                     break;
35 
36                 case MotionEvent.ACTION_CANCEL:
37                    ....
38                     break;
39 
40                 case MotionEvent.ACTION_MOVE:
41                     ....
42                     break;
43             }
44 
45             return true;
46         }
47 
48         return false;
49     }