一、Android事件的分發機制
這裏需要了解下Andorid事件的分發機制。事件分發一般是針對一組事件，即ACTION_DOWN > ACTION_UP 或 ACTION_DOWN > ACTION_MOVE... >ACTION_UP，其中涉及事件分發的主要方法有 dispatchTouchEvent(MotionEvent event)、onInterceptTouchEvent(MotionEvent event) (ViewGroup有，View沒有)、onTouchEvent(MotionEvent event)，而且事件分發是由上向下傳遞的，即先到parent，再到child，這裏簡單以 ViewGroup內包裹一個View爲例，大致分析下其事件的分發流程（忽略Activity，Window的傳遞）
事件首先會傳遞到ViewGroup.dispatchTouchEvent(MotionEvent event)，然後會判斷ViewGroup.onInterceptTouchEvent(MotionEvent event)的返回值：
1.如果返回爲false，即不攔截，事件則會傳遞給View.dispatchTouchEvent(MotionEvent event)，由於這裏View沒有子View了，事件則傳遞給該View的View.onTouchEvent(MotionEvent event)處理，如果View.onTouchEvent(MotionEvent event)沒有消耗該事件，則該事件會返回給ViewGroup.onTouchEvent(MotionEvent event)處理，如果View.onTouchEvent(MotionEvent event)消耗了該事件，則該事件不會再返回給ViewGroup，本次事件分發結束。
2.如果ViewGroup.onInterceptTouchEvent(MotionEvent event)返回值爲ture，即攔截事件，則事件將由ViewGroup.onTouchEvent(MotionEvent event)處理，本次事件分發結束。
3.即使事件被ViewGroup攔截了，View也可以阻止ViewGroup對事件的攔截。可以通過getParent().requestDisallowInterceptTouchEvent(true)。
大致流程圖
前面說到View可以阻止ViewGroup對事件的攔截，但除了ACTION_DOWN，也就是說，對一組事件，除了ACTION_DOWN，子View可以在ViewGroup.onInterceptTouchEvent(MotionEvent event)返回ture的情況下，獲取事件的處理權，下面截圖android25的源代碼。
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;
}@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);
}
}當actionMasked == MotionEvent.ACTION_DOWN||mFirstTouchTarget !=null時，會進行disallowIntercept的判斷，而disallowIntercept取決於mGroupFlags，因爲FLAG_DISALLOW_INTERCEPT是一個常量0x80000，而mGroupFlags的賦值是可以通過requestDisallowInterceptTouchEvent來改變的。當requestDisallowInterceptTouchEvent(true)，disallowIntercept=true,此時不走onInterceptTouchEvent(ev)的判斷，intercepted=false從而達到阻止ViewGroup攔截的效果。
二、以RecyclerView下拉刷新上拉加載更多爲例分析滑動衝突及解決
以recyclerView爲例，也可以換listView。默認狀態時紅色部分爲可視部分，也就是頂部和底部隱藏看不見，這裏我們選擇FrameLayout作爲容器，因此，FrameLayout和RecyclerView就會產生同向滑動衝突。只有recyclerView內容滑動到頂部並且手勢爲下滑時，header纔會慢慢下滑到可視範圍內，或recyclerView內容滑動到底部時，並且手勢爲上滑，footer纔會慢慢上滑到可視範圍內。
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;
}2.MotionEvent.ACTION_UP中也必須返回false，因爲一組事件以ACTION_UP結尾，則ACTION_UP這個事件必定會經過FrameLayout.onTouchEvent(ev)，如果攔截了，則子View針對ACTION_UP需要處理的事情就無法完成。
3.MotionEvent.ACTION_MOVE中根據實際情況判斷是否攔截。
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();
}
不完善點還待指正！！！