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以下源码基于Gingerbread 2.3.7
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1、先看ViewGroup的dispatchOnTouchEvent(MotionEvent e)的源码
1.1 主要是获取一些坐标值，留备后用
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
if (!onFilterTouchEventForSecurity(ev)) {
return false;
} final int action = ev.getAction();
final float xf = ev.getX();
final float yf = ev.getY();
final float scrolledXFloat = xf + mScrollX;
final float scrolledYFloat = yf + mScrollY;
final Rect frame = mTempRect;
1.2 先处理DOWN事件
//TODO 1、判断是不是子View不允许老子拦截Touch事件
boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0; if (action == MotionEvent.ACTION_DOWN) {
if (mMotionTarget != null) {
// this is weird, we got a pen down, but we thought it was
// already down!
// XXX: We should probably send an ACTION_UP to the current
// target.
mMotionTarget = null;
}
// If we're disallowing intercept or if we're allowing and we didn't
// intercept
//TODO 2、如果子View不允许，或者老子自己不想拦截，则进入这里
if (disallowIntercept || !onInterceptTouchEvent(ev)) {
// reset this event's action (just to protect ourselves)
ev.setAction(MotionEvent.ACTION_DOWN);
// We know we want to dispatch the event down, find a child
// who can handle it, start with the front-most child.
final int scrolledXInt = (int) scrolledXFloat;
final int scrolledYInt = (int) scrolledYFloat;
final View[] children = mChildren;
final int count = mChildrenCount;
//TODO 3、根据用户落指的坐标，找到应该响应该Touch事件的子View或者子ViewGroup
for (int i = count - 1; i >= 0; i--) {
final View child = children[i];
if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE
|| child.getAnimation() != null) {
child.getHitRect(frame);
//TODO 4、很明显，根据范围来判断的
if (frame.contains(scrolledXInt, scrolledYInt)) {
// offset the event to the view's coordinate system
final float xc = scrolledXFloat - child.mLeft;
final float yc = scrolledYFloat - child.mTop;
ev.setLocation(xc, yc);
child.mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;
//TODO 5、找到子View，将事件交给它，如果它愿意消费DOWN事件，则记录下来这个龟儿子，并返回
if (child.dispatchTouchEvent(ev)) {
// Event handled, we have a target now.
mMotionTarget = child;
return true;
}
// The event didn't get handled, try the next view.
// Don't reset the event's location, it's not
// necessary here.
}
}
}
}
}
看见上面5条注释了吧，够用了
1.3 没找到子View、子View不愿消费(注释5)、或者不是DOWN事件，如下
boolean isUpOrCancel = (action == MotionEvent.ACTION_UP) ||
(action == MotionEvent.ACTION_CANCEL); if (isUpOrCancel) {
// Note, we've already copied the previous state to our local
// variable, so this takes effect on the next event
mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT;
} // The event wasn't an ACTION_DOWN, dispatch it to our target if
// we have one.
12 // TODO 1、如果是没有子View，不管是DOWN还是其他事件，都交给自己来处理，包括后续的MOVE、UP事件。
13 // 因为这个方法有点类似递归调用，所以如果自己也不想处理，那么父类会分发给自己
final View target = mMotionTarget;
if (target == null) {
// We don't have a target, this means we're handling the
// event as a regular view.
ev.setLocation(xf, yf);
if ((mPrivateFlags & CANCEL_NEXT_UP_EVENT) != 0) {
ev.setAction(MotionEvent.ACTION_CANCEL);
mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;
}
// TODO 2、调用View的dispatchTouchEvent，会调用到自己的onTouchEvent()方法
return super.dispatchTouchEvent(ev);
}
这段代码就一个意思，不管啥事件，没有子View，老子亲自处理~
1.4 找到子View，继续往下走
1 // TODO 1、找到子View，子View让老子拦截，或者老子自己想拦截，给龟孙一个CANCEL，
2 // 并告诉父ViewGroup，老子要了，而且将mMotionTarget置为null，这样后续事件直接走上面的判断，直接找老子处理
// if have a target, see if we're allowed to and want to intercept its
// events
if (!disallowIntercept && onInterceptTouchEvent(ev)) {
final float xc = scrolledXFloat - (float) target.mLeft;
final float yc = scrolledYFloat - (float) target.mTop;
mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;
ev.setAction(MotionEvent.ACTION_CANCEL);
ev.setLocation(xc, yc);
if (!target.dispatchTouchEvent(ev)) {
// target didn't handle ACTION_CANCEL. not much we can do
// but they should have.
}
// clear the target
mMotionTarget = null;
// Don't dispatch this event to our own view, because we already
// saw it when intercepting; we just want to give the following
// event to the normal onTouchEvent().
return true;
} // TODO 2、如果是UP、CANCEL事件，则清空
if (isUpOrCancel) {
mMotionTarget = null;
}
这段代码，龟孙之前说的好好的， 要自己消费事件，突然又不想了。或者老子突然想拦截了，那么老子自己拦截，自己处理
1.5 没有幺蛾子了，交给龟孙自己处理
// finally offset the event to the target's coordinate system and
// dispatch the event.
final float xc = scrolledXFloat - (float) target.mLeft;
final float yc = scrolledYFloat - (float) target.mTop;
ev.setLocation(xc, yc); if ((target.mPrivateFlags & CANCEL_NEXT_UP_EVENT) != 0) {
ev.setAction(MotionEvent.ACTION_CANCEL);
target.mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;
mMotionTarget = null;
} // TODO 1、不管前面这几行了，交给龟孙去处理
return target.dispatchTouchEvent(ev);
ViewGroup没有重写View的onTouchEvent()方法，onInterceptTouchEvent()返回false，默认不拦截
2、 View的相关方法
2.1 dispatchTouchEvent()方法
就一点点，调用自己的onTouchEvent()方法，并以onTouchEvent的返回值为返回值
/**
* Pass the touch screen motion event down to the target view, or this
* view if it is the target.
*
* @param event The motion event to be dispatched.
* @return True if the event was handled by the view, false otherwise.
*/
public boolean dispatchTouchEvent(MotionEvent event) {
if (!onFilterTouchEventForSecurity(event)) {
return false;
} if (mOnTouchListener != null && (mViewFlags & ENABLED_MASK) == ENABLED &&
mOnTouchListener.onTouch(this, event)) {
return true;
}
return onTouchEvent(event);
}
2.2 onTouchEvent()方法
这个方法比较复杂，不可点击的时候返回false，说明自己不处理。可点击的时候，根据不同的事件类型进行处理
public boolean onTouchEvent(MotionEvent event) {
final int viewFlags = mViewFlags;
if ((viewFlags & ENABLED_MASK) == DISABLED) {
// A disabled view that is clickable still consumes the touch
// events, it just doesn't respond to them.
return (((viewFlags & CLICKABLE) == CLICKABLE ||
(viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE));
}
if (mTouchDelegate != null) {
if (mTouchDelegate.onTouchEvent(event)) {
return true;
}
}
if (((viewFlags & CLICKABLE) == CLICKABLE ||
(viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)) {
switch (event.getAction()) {
case MotionEvent.ACTION_UP:
boolean prepressed = (mPrivateFlags & PREPRESSED) != 0;
if ((mPrivateFlags & PRESSED) != 0 || prepressed) {
// take focus if we don't have it already and we should in
// touch mode.
boolean focusTaken = false;
if (isFocusable() && isFocusableInTouchMode() && !isFocused()) {
focusTaken = requestFocus();
}
if (!mHasPerformedLongPress) {
// This is a tap, so remove the longpress check
removeLongPressCallback();
// Only perform take click actions if we were in the pressed state
if (!focusTaken) {
// Use a Runnable and post this rather than calling
// performClick directly. This lets other visual state
// of the view update before click actions start.
if (mPerformClick == null) {
mPerformClick = new PerformClick();
}
if (!post(mPerformClick)) {
performClick();
}
}
}
if (mUnsetPressedState == null) {
mUnsetPressedState = new UnsetPressedState();
}
if (prepressed) {
mPrivateFlags |= PRESSED;
refreshDrawableState();
postDelayed(mUnsetPressedState,
ViewConfiguration.getPressedStateDuration());
} else if (!post(mUnsetPressedState)) {
// If the post failed, unpress right now
mUnsetPressedState.run();
}
removeTapCallback();
}
break;
case MotionEvent.ACTION_DOWN:
if (mPendingCheckForTap == null) {
mPendingCheckForTap = new CheckForTap();
}
mPrivateFlags |= PREPRESSED;
mHasPerformedLongPress = false;
postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());
break;
case MotionEvent.ACTION_CANCEL:
mPrivateFlags &= ~PRESSED;
refreshDrawableState();
removeTapCallback();
break;
case MotionEvent.ACTION_MOVE:
final int x = (int) event.getX();
final int y = (int) event.getY();
// Be lenient about moving outside of buttons
int slop = mTouchSlop;
if ((x < 0 - slop) || (x >= getWidth() + slop) ||
(y < 0 - slop) || (y >= getHeight() + slop)) {
// Outside button
removeTapCallback();
if ((mPrivateFlags & PRESSED) != 0) {
// Remove any future long press/tap checks
removeLongPressCallback();
// Need to switch from pressed to not pressed
mPrivateFlags &= ~PRESSED;
refreshDrawableState();
}
}
break;
}
return true;
}
return false;
}