提纲

• 事件分发的事件有哪些，涉及到哪些方法
• 事件分发怎么从Activity传入到View
• View的事件分发
• ViewGroup的事件分发

1. 事件分发的事件有哪些，涉及到哪些方法

• 当用户触摸点击屏幕时，将会产生事件，在android中为MotionEvent在这个类中有很多静态常量：

• 默认情况下事件分发会按照由Activity到ViewGroup再到View的顺序进行分发
• 事件的传递流程是从PhoneWindow->DecorView(mDecor是getWindow().getDecorView()返回的View，通过setContentView设置的View是该View的子View)，再传递到Activity的View树。

1.View的事件分发的重要的方法：diapatchTouchEvent和touchEvent,onClick

|---View
|   |---boolean dispatchTouchEvent(MotionEvent event)
|   |--- boolean onTouchEvent(MotionEvent event)
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1.1 dispatchTouchEvent: 如果事件由视图处理，则为true，否则为false。

public boolean dispatchTouchEvent(MotionEvent event) {
        // If the event should be handled by accessibility focus first.
        if (event.isTargetAccessibilityFocus()) {
            // We don't have focus or no virtual descendant has it, do not handle the event.
            if (!isAccessibilityFocusedViewOrHost()) {
                return false;
            }
            // We have focus and got the event, then use normal event dispatch.
            event.setTargetAccessibilityFocus(false);
        }

        boolean result = false;

        if (mInputEventConsistencyVerifier != null) {
            mInputEventConsistencyVerifier.onTouchEvent(event, 0);
        }

        final int actionMasked = event.getActionMasked();
        if (actionMasked == MotionEvent.ACTION_DOWN) {
            // Defensive cleanup for new gesture
            stopNestedScroll();
        }

        if (onFilterTouchEventForSecurity(event)) {
            if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {
                result = true;
            }
            // 重点 判断listenerInfo 中是否有事件listenter 并且mOnTouchListener.onTouc 返回true 
            ListenerInfo li = mListenerInfo;
            if (li != null && li.mOnTouchListener != null
                    && (mViewFlags & ENABLED_MASK) == ENABLED
                    && li.mOnTouchListener.onTouch(this, event)) {
                result = true;
            }
                        // 第二个重点，如果上述判断为false,并且 onTouchEventr返回为true,消耗事件
            if (!result && onTouchEvent(event)) {
                result = true;
            }
        }

        if (!result && mInputEventConsistencyVerifier != null) {
            mInputEventConsistencyVerifier.onUnhandledEvent(event, 0);
        }

        // 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();
        }

        return result;
    }

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1. dispatchTouchEvent中final int actionMasked = event.getActionMasked();
2. ListenerInfo :将view所有的listener信息封装到一个对象中。
3. 在该方法中有两个判断：

 ListenerInfo li = mListenerInfo;
            if (li != null && li.mOnTouchListener != null
                    && (mViewFlags & ENABLED_MASK) == ENABLED
                    && li.mOnTouchListener.onTouch(this, event)) {
                result = true;
            }

            if (!result && onTouchEvent(event)) {
                result = true;
            }
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如果onTouchEvent或者是onTouchListenner是true的话，会消费此事件，同时，在这里也走了onTouchEvent

• boolean onTouchEvent
• MotionEvent.ACTION_UP:调用了PerformClick()

三个问题：

1. 在activity中调用了

 mTouchView.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                Log.e("TAG", "onTouch: " + event.getAction());
                return false;
            }
        });
        mTouchView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Log.e("TAG", "onClick: " );
            }
        });

     /***********TabLayout************/   
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        Log.e("TAG", "onTouchEvent: "+event.getAction());
        return super.onTouchEvent(event);
    }
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执行顺序：

2. 如果是Tablyout中直接return ture呢？

不执行onClick,因为onClick在View.OntouchEvent中的ACTION_UP中，若直接return true 就不会走super中的方法。

3. 如果是dispatchEvent return true呢？

什么都不执行

分发流程

super.dispatchEvent->ListenerInfo->super.onTouchEvent(event)->ACTION_UP->performListener().
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2. ViewGroup的事件分发：

首先是actionDown:

 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;
                }
            }
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• mFirstTouchTarget: 这个很重要,只有在第一次按下的时候才会调用disallowIntercept,如果之后想要改变效果的时候，这是一个坑。

|---ViewGroup
|   |---dispatchTouchEvent
|   |   |---onInterceptTouchEvent(ev)
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有View会消耗时间的情况（比如点击，onTouchListener）

• 第一次按下进来(down)--->ViewGroup.dispatchTouchEvent--->ViewGroup.onInterceptTouchEvent(ev)-->view.dispatchEvent---(view的那一套)

• 第二次进来（move）ViewGroup.dispatchTouchEvent--->ViewGroup.onInterceptTouchEvent(ev)-->view.dispatchEvent---(view的那一套)

• 第三次（up））ViewGroup.dispatchTouchEvent--->ViewGroup.onInterceptTouchEvent(ev)-->view.dispatchEvent---(view的那一套)-->view.onClick

子View中没有消费事件的情况。只走一遍

• 第一次进来(down)ViewGroup.dispatchTouchEvent--->ViewGroup.onInterceptTouchEvent(ev)-->view.dispatchEvent---view.onTouch-->onTouch Event

viewGroup的源码分析

actionDown

 /**
     * 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; //清除target
        }
    }
<!--------------------------------------------------->
      if (!canceled && !intercepted) // intercepted 默认是没有拦截
      {
         if (newTouchTarget == null && childrenCount != 0) {
              for (int i = childrenCount - 1; i >= 0; i--) {//反序列的for循环 先拿最上面的layout
                if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
                }
              }
         }
      }

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/**
     * Transforms a motion event into the coordinate space of a particular child view,
     * filters out irrelevant pointer ids, and overrides its action if necessary.
     * If child is null, assumes the MotionEvent will be sent to this ViewGroup instead.
     */
    private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,
            View child, int desiredPointerIdBits) {
        final boolean handled;
        final int oldAction = event.getAction();
        if (cancel || oldAction == MotionEvent.ACTION_CANCEL) {
            event.setAction(MotionEvent.ACTION_CANCEL);
            if (child == null) {
                handled = super.dispatchTouchEvent(event);
            } else {
                handled = child.dispatchTouchEvent(event);
            }
            event.setAction(oldAction);
            return handled;
        }

        // Calculate the number of pointers to deliver.
        final int oldPointerIdBits = event.getPointerIdBits();
        final int newPointerIdBits = oldPointerIdBits & desiredPointerIdBits;

        // If for some reason we ended up in an inconsistent state where it looks like we
        // might produce a motion event with no pointers in it, then drop the event.
        if (newPointerIdBits == 0) {
            return false;
        }
        final MotionEvent transformedEvent;
        if (newPointerIdBits == oldPointerIdBits) {
            if (child == null || child.hasIdentityMatrix()) {
                if (child == null) {
                    handled = super.dispatchTouchEvent(event);
                } else {
                    final float offsetX = mScrollX - child.mLeft;
                    final float offsetY = mScrollY - child.mTop;
                    event.offsetLocation(offsetX, offsetY);

                    handled = child.dispatchTouchEvent(event);

                    event.offsetLocation(-offsetX, -offsetY);
                }
                return handled;
            }
            transformedEvent = MotionEvent.obtain(event);
        } else {
            transformedEvent = event.split(newPointerIdBits);
        }

        // Perform any necessary transformations and dispatch.
        if (child == null) {
            handled = super.dispatchTouchEvent(transformedEvent);
        } else {
            final float offsetX = mScrollX - child.mLeft;
            final float offsetY = mScrollY - child.mTop;
            transformedEvent.offsetLocation(offsetX, offsetY);
            if (! child.hasIdentityMatrix()) {
                transformedEvent.transform(child.getInverseMatrix());
            }

            handled = child.dispatchTouchEvent(transformedEvent);
        }

        // Done.
        transformedEvent.recycle();
        return handled;
    }

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