响应点击事件
public boolean performClick() {
sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
if (mOnClickListener != null) {
playSoundEffect(SoundEffectConstants.CLICK);
mOnClickListener.onClick(this);
return true;
}
return false;
}
里面执行mOnClickListener.onClick(this);即回调绑定监听器的onClick()函数。
关键点：
onTouch和onTouchEvent的区别，又该如何使用？
答：
当view控件接受到触摸事件，如果控件绑定了onTouchListener监听器，而且该控件是enable，那么就去执行onTouch()方法，如果返回true，则已经把触摸事件消费掉，不再向下传递；如果返回false，那么继续调用onTouchEvent()事件。
Android的Touch事件传递到Activity顶层的DecorView(一个FrameLayout)之后，会通过ViewGroup一层层往视图树的上面传递，最终将事件传递给实际接收的View。下面给出一些重要的方法。
dispatchTouchEvent
事件传递到一个ViewGroup上面时，会调用dispatchTouchEvent。代码有删减
public boolean dispatchTouchEvent(MotionEvent ev) {
boolean handled = false;
if (onFilterTouchEventForSecurity(ev)) {
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;
// Attention 1 ：在按下时候清除一些状态
if (actionMasked == MotionEvent.ACTION_DOWN) {
cancelAndClearTouchTargets(ev);
//注意这个方法
resetTouchState();
}
// Attention 2：检查是否需要拦截
final boolean intercepted;
//如果刚刚按下 或者 已经有子View来处理
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 {
// 不是一个动作序列的开始 同时也没有子View来处理，直接拦截
intercepted = true;
}
//事件没有取消 同时没有被当前ViewGroup拦截，去找是否有子View接盘
if (!canceled && !intercepted) {
//如果这是一系列动作的开始 或者有一个新的Pointer按下 我们需要去找能够处理这个Pointer的子View
if (actionMasked == MotionEvent.ACTION_DOWN
|| (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)
|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
final int actionIndex = ev.getActionIndex(); // always 0 for down
//上面说的触碰点32的限制就是这里导致
final int idBitsToAssign = split ? 1 << ev.getPointerId(actionIndex)
: TouchTarget.ALL_POINTER_IDS;
final int childrenCount = mChildrenCount;
if (newTouchTarget == null && childrenCount != 0) {
final float x = ev.getX(actionIndex);
final float y = ev.getY(actionIndex);
//对当前ViewGroup的所有子View进行排序，在上层的放在开始
final ArrayList<View> preorderedList = buildOrderedChildList();
final boolean customOrder = preorderedList == null
&& isChildrenDrawingOrderEnabled();
final View[] children = mChildren;
for (int i = childrenCount - 1; i >= 0; i--) {
final int childIndex = customOrder
? getChildDrawingOrder(childrenCount, i) : i;
final View child = (preorderedList == null)
? children[childIndex] : preorderedList.get(childIndex);
// canViewReceivePointerEvents visible的View都可以接受事件
// isTransformedTouchPointInView 计算是否落在点击区域上
if (!canViewReceivePointerEvents(child)
|| !isTransformedTouchPointInView(x, y, child, null)) {
ev.setTargetAccessibilityFocus(false);
continue;
}
//能够处理这个Pointer的View是否已经处理之前的Pointer，那么把
newTouchTarget = getTouchTarget(child);
if (newTouchTarget != null) {
// Child is already receiving touch within its bounds.
// Give it the new pointer in addition to the ones it is handling.
newTouchTarget.pointerIdBits |= idBitsToAssign;
break;
} }
//Attention 3 : 直接发给子View
if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
// Child wants to receive touch within its bounds.
mLastTouchDownTime = ev.getDownTime();
if (preorderedList != null) {
// childIndex points into presorted list, find original index
for (int j = 0; j < childrenCount; j++) {
if (children[childIndex] == mChildren[j]) {
mLastTouchDownIndex = j;
break;
}
}
} else {
mLastTouchDownIndex = childIndex;
}
mLastTouchDownX = ev.getX();
mLastTouchDownY = ev.getY();
newTouchTarget = addTouchTarget(child, idBitsToAssign);
alreadyDispatchedToNewTouchTarget = true;
break;
}
}
}
}
}
// 前面已经找到了接收事件的子View，如果为NULL，表示没有子View来接手，当前ViewGroup需要来处理
if (mFirstTouchTarget == null) {
// ViewGroup处理
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
} else {
if(alreadyDispatchedToNewTouchTarget) {
//ignore some code
if (dispatchTransformedTouchEvent(ev, cancelChild,
target.child, target.pointerIdBits)) {
handled = true;
}
}
}
return handled;
}
