一、Android事件的分发机制

这里需要了解下Andorid事件的分发机制。事件分发一般是针对一组事件，即ACTION_DOWN > ACTION_UP 或 ACTION_DOWN > ACTION_MOVE... >ACTION_UP，其中涉及事件分发的主要方法有 dispatchTouchEvent(MotionEvent event)、onInterceptTouchEvent(MotionEvent event) (ViewGroup有，View没有)、onTouchEvent(MotionEvent event)，而且事件分发是由上向下传递的，即先到parent，再到child，这里简单以 ViewGroup内包裹一个View为例，大致分析下其事件的分发流程（忽略Activity，Window的传递）

事件首先会传递到ViewGroup.dispatchTouchEvent(MotionEvent event)，然后会判断ViewGroup.onInterceptTouchEvent(MotionEvent event)的返回值：

1.如果返回为false，即不拦截，事件则会传递给View.dispatchTouchEvent(MotionEvent event)，由于这里View没有子View了，事件则传递给该View的View.onTouchEvent(MotionEvent event)处理，如果View.onTouchEvent(MotionEvent event)没有消耗该事件，则该事件会返回给ViewGroup.onTouchEvent(MotionEvent event)处理，如果View.onTouchEvent(MotionEvent event)消耗了该事件，则该事件不会再返回给ViewGroup，本次事件分发结束。

2.如果ViewGroup.onInterceptTouchEvent(MotionEvent event)返回值为ture，即拦截事件，则事件将由ViewGroup.onTouchEvent(MotionEvent event)处理，本次事件分发结束。

3.即使事件被ViewGroup拦截了，View也可以阻止ViewGroup对事件的拦截。可以通过getParent().requestDisallowInterceptTouchEvent(true)。

大致流程图

前面说到View可以阻止ViewGroup对事件的拦截，但除了ACTION_DOWN，也就是说，对一组事件，除了ACTION_DOWN，子View可以在ViewGroup.onInterceptTouchEvent(MotionEvent event)返回ture的情况下，获取事件的处理权，下面截图android25的源代码。

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;}

@Overridepublic void requestDisallowInterceptTouchEvent(boolean disallowIntercept) {if (disallowIntercept == ((mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0)) {// We're already in this state, assume our ancestors are tooreturn;}if (disallowIntercept) {mGroupFlags |= FLAG_DISALLOW_INTERCEPT;} else {mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT;}// Pass it up to our parentif (mParent != null) {mParent.requestDisallowInterceptTouchEvent(disallowIntercept);}}

当actionMasked == MotionEvent.ACTION_DOWN||mFirstTouchTarget !=null时，会进行disallowIntercept的判断，而disallowIntercept取决于mGroupFlags，因为FLAG_DISALLOW_INTERCEPT是一个常量0x80000，而mGroupFlags的赋值是可以通过requestDisallowInterceptTouchEvent来改变的。当requestDisallowInterceptTouchEvent(true)，disallowIntercept=true,此时不走onInterceptTouchEvent(ev)的判断，intercepted=false从而达到阻止ViewGroup拦截的效果。

二、以RecyclerView下拉刷新上拉加载更多为例分析滑动冲突及解决

以recyclerView为例，也可以换listView。默认状态时红色部分为可视部分，也就是顶部和底部隐藏看不见，这里我们选择FrameLayout作为容器，因此，FrameLayout和RecyclerView就会产生同向滑动冲突。只有recyclerView内容滑动到顶部并且手势为下滑时，header才会慢慢下滑到可视范围内，或recyclerView内容滑动到底部时，并且手势为上滑，footer才会慢慢上滑到可视范围内。

private boolean intercept;private float lastInterceptY;@Overridepublic boolean onInterceptTouchEvent(MotionEvent ev) {float curInterceptY = ev.getY();switch (ev.getAction()) {case MotionEvent.ACTION_DOWN:intercept = false;break;case MotionEvent.ACTION_MOVE:if (isRefreshing || isLoadMore) {intercept = false;} else {boolean isHeaderShow = headerParams.topMargin > -headerHeight;boolean isFooterShow = footerParams.topMargin < height;intercept = touchHelper != null && touchHelper.judgeIntercept(curInterceptY, lastInterceptY, isHeaderShow, isFooterShow, allowLoadMore);}break;case MotionEvent.ACTION_UP:intercept = false;break;}lastInterceptY = curInterceptY;return intercept;}

@Overridepublic boolean judgeIntercept(float curInterceptY, float lastInterceptY, boolean isHeaderShow, boolean isFooterShow, boolean allowLoadMore) {boolean intercept;int firstVisiblePos = layoutManager.findFirstVisibleItemPosition();View firstView = rv.getChildAt(firstVisiblePos);if (firstVisiblePos == 0 && firstView.getTop() == 0) {intercept = curInterceptY > lastInterceptY || isHeaderShow;} else {if (allowLoadMore && layoutManager.findLastVisibleItemPosition() == layoutManager.getItemCount() - 1) {intercept = curInterceptY < lastInterceptY || isFooterShow;} else {intercept = false;}}return intercept;}

1.MotionEvent.ACTION_DOWN中，必须返回false，不拦截，一旦拦截，后续的ACTION_MOVE和ACTION_UP将直接交由FrameLayout的onTouchEvent(ev)处理

2.MotionEvent.ACTION_UP中也必须返回false，因为一组事件以ACTION_UP结尾，则ACTION_UP这个事件必定会经过FrameLayout.onTouchEvent(ev)，如果拦截了，则子View针对ACTION_UP需要处理的事情就无法完成。

3.MotionEvent.ACTION_MOVE中根据实际情况判断是否拦截。

private float moveDis;@Overridepublic boolean onTouchEvent(MotionEvent ev) {if (touchHelper != null) {float curTouchY = ev.getY();switch (ev.getAction()) {case MotionEvent.ACTION_DOWN:break;case MotionEvent.ACTION_MOVE:moveDis = curTouchY - lastInterceptY;if (Math.abs(moveDis) < touchSlop) {break;}if (isRefreshing || isLoadMore) {break;}moveDis = moveDis * kMoveFactor;if (touchHelper.isContentSlideToTop()) {updateHeaderMargin(moveDis);} else if (touchHelper.isContentSlideToBottom()) {updateFooterMargin(moveDis);}break;case MotionEvent.ACTION_UP:if (moveDis > 0) {if (touchHelper.isContentSlideToTop()) {if (headerParams.topMargin < 0) {scrollHeaderByAnimator(headerParams.topMargin, -headerHeight);if (header != null) {header.onPullToRefresh(moveDis);}} else {scrollHeaderByAnimator(headerParams.topMargin, 0);if (header != null) {header.onRefreshing();}isRefreshing = true;if (listener != null) {listener.onRefresh();}}}} else {if (touchHelper.isContentSlideToBottom()) {if (footerParams.topMargin > height - footerHeight) {scrollFooterByAnimator(false, footerParams.topMargin, height);if (footer != null) {footer.onPullToLoadMore(moveDis);}} else {scrollFooterByAnimator(false, footerParams.topMargin, height - footerHeight);if (footer != null) {footer.onLoadMore();}isLoadMore = true;if (listener != null) {listener.onLoadMore();}}}}break;}}return true;}

private void updateHeaderMargin(float moveDis) {moveDis = moveDis < 0 ? 0 : moveDis;headerParams.topMargin = (int) (-headerHeight + moveDis);headerVG.setLayoutParams(headerParams);setChildViewTopMargin((int) moveDis);if (header != null) {if (moveDis < headerHeight) {header.onPullToRefresh(moveDis);} else {header.onReleaseToRefresh(moveDis);}}}private void setChildViewTopMargin(int topMargin) {LayoutParams childParams = (LayoutParams) childView.getLayoutParams();childParams.topMargin = topMargin;childView.setLayoutParams(childParams);}private void updateFooterMargin(float moveDis) {moveDis = moveDis > 0 ? 0 : moveDis;footerParams.topMargin = (int) (height + moveDis);footerVG.setLayoutParams(footerParams);setChildViewBottomMargin((int) Math.abs(moveDis));scrollContentToBottom((int) -moveDis);if (footer != null) {if (Math.abs(moveDis) < footerHeight) {footer.onPullToLoadMore(moveDis);} else {footer.onReleaseToLoadMore(moveDis);}}}private void setChildViewBottomMargin(int bottomMargin) {LayoutParams childParams = (LayoutParams) childView.getLayoutParams();childParams.bottomMargin = bottomMargin;childView.setLayoutParams(childParams);}private void scrollContentToBottom(int deltaY) {if (childView instanceof RecyclerView) {childView.scrollBy(0, deltaY);} else if (childView instanceof ListView) {((ListView) childView).smoothScrollBy(deltaY, 0);} else if (childView instanceof ScrollView) {childView.scrollBy(0, deltaY);}}private void scrollHeaderByAnimator(float startY, float endY) {ValueAnimator animator = ValueAnimator.ofFloat(startY, endY);animator.setDuration(kDuration);animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {@Overridepublic void onAnimationUpdate(ValueAnimator animation) {float floatValue = (float) animation.getAnimatedValue();headerParams.topMargin = (int) floatValue;headerVG.setLayoutParams(headerParams);setChildViewTopMargin((int) (headerHeight + floatValue));}});animator.start();}private void scrollFooterByAnimator(final boolean isAuto, float startY, float endY) {ValueAnimator animator = ValueAnimator.ofFloat(startY, endY);animator.setDuration(kDuration);animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {@Overridepublic void onAnimationUpdate(ValueAnimator animation) {float floatValue = (float) animation.getAnimatedValue();footerParams.topMargin = (int) floatValue;footerVG.setLayoutParams(footerParams);int bottomMargin = (int) (height - floatValue);setChildViewBottomMargin(bottomMargin);if (isAuto) {scrollContentToBottom(bottomMargin);if (footer != null) {footer.onPullToLoadMore(bottomMargin);if (bottomMargin == footerHeight) {footer.onLoadMore();}}}}});animator.start();}

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不完善点还待指正！！！