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。
@Override
public void requestDisallowInterceptTouchEvent(boolean disallowIntercept) {
if (disallowIntercept == ((mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0)) {
// We're already in this state, assume our ancestors are too
return;
}
if (disallowIntercept) {
mGroupFlags |= FLAG_DISALLOW_INTERCEPT;
} else {
mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT;
}
// Pass it up to our parent
if (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;
@Override
public 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;
}
@Override
public 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;
@Override
public 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() {
@Override
public 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() {
@Override
public 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();
}
不完善点还待指正！！！
源码下载：下拉刷新上拉加载更多 喜欢就star下吧！万分感谢！！！
网友评论