一、ViewGroup的onInterceptTouchEvent源码分析
onInterceptTouchEvent比较简单先看他的源码
public boolean onInterceptTouchEvent(MotionEvent ev) {
//1、判断是否是鼠标设备操作
//2、ACTION_DOWN事件
//3、是否是首要按钮按下，如鼠标左键
//4、是否是滑动条
//看意思以上是兼容安卓非手机设备用的判断，满足的话，就返回true，拦截事件分发
if (ev.isFromSource(InputDevice.SOURCE_MOUSE)
&& ev.getAction() == MotionEvent.ACTION_DOWN
&& ev.isButtonPressed(MotionEvent.BUTTON_PRIMARY)
&& isOnScrollbarThumb(ev.getX(), ev.getY())) {
return true;
}
//默认返回false不拦截事件分发
return false;
}onInterceptTouchEvent 作用就是要不要拦截向子View分发事件，如果想拦截的话，需要重写onInterceptTouchEvent。
二、ViewGroup的dispatchTouchEvent源码分析
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
//如果输入一致性检查事件不为null，先执行输入前后一致性检查
//源码英文注释说是为了debug的目的，估计是设置断点后，再次运行的时候，为了不丢失事件，检查是否是同一个输入，可忽略
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onTouchEvent(ev, 1);
}
// If the event targets the accessibility focused view and this is it, start
// normal event dispatch. Maybe a descendant is what will handle the click.
//如果事件对象是容易获取焦点的view，开始普通事件分发，可能是某个后代会处理点击。
//貌似是用来判断 motion event是否设置了容易获取焦点Flags
//这个flags是FLAG是_WINDOW_IS_OBSCURED，源码意思大约是设置事件对象，是否部分或者全部被遮挡到了
if (ev.isTargetAccessibilityFocus() && isAccessibilityFocusedViewOrHost()) {
ev.setTargetAccessibilityFocus(false);
}
//handled 是最终要返回的结果值
boolean handled = false;
//onFilterTouchEventForSecurity 对事件进行安全检查，如果true可执行，false就放弃
//onFilterTouchEventForSecurity 里面进行了是否要遮挡进行过滤，以及event的对象是否被遮挡的两个判断
if (onFilterTouchEventForSecurity(ev)) {
//未被遮挡进入了此if内部
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;
// Handle an initial down.
//处理最初的ACTION_DOWN事件
if (actionMasked == MotionEvent.ACTION_DOWN) {
// Throw away all previous state when starting a new touch gesture.
// The framework may have dropped the up or cancel event for the previous gesture
// due to an app switch, ANR, or some other state change.
//当开始了一个新的手势，抛弃了之前所有的状态
//由于app切换，ANR或者其他状态改变，框架可能已经放弃了对前一个手势的Up 和cancel的处理
//cancelAndClearTouchTargets 清空了之前所有的找到的触摸对象，里面调用了dispatchTransformedTouchEvent(event, true, target.child, target.pointerIdBits);对子View的事件进行了取消，传递的第二个参数true 是是否取消的标志
//里面调用了clearTouchTargets 对比较重要的mFirstTouchTarget对象赋值null
//mFirstTouchTarget的英文注释 First touch target in the linked list of touch targets.是第一个找到的触摸对象
cancelAndClearTouchTargets(ev);
resetTouchState();
}
//检查是否拦截
// Check for interception.
final boolean intercepted;
//第一种情况ACTION_DOWN的时候判断拦截，
//第二种情况，已经找到了要处理事件的字View或者子ViewGroup
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
//之后又对disallowIntercept进行了判断，disallowIntercept的意思是，是否禁用拦截，disallowIntercept可以使用requestDisallowInterceptTouchEvent方法自己进行设置，后面会具体分析
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
if (!disallowIntercept) {
//没有禁用拦截，就会根据拦截函数onInterceptTouchEvent的返回值，进行拦截判断，是否拦截
intercepted = onInterceptTouchEvent(ev);
ev.setAction(action); // restore action in case it was changed恢复action，防止action被改变了
} else {//禁止拦截，所以设置拦截标识为不拦截
intercepted = false;
}
} else {
// There are no touch targets and this action is not an initial down
// so this view group continues to intercept touches.
//没有找到处理MotionEvent的目标对象，而且也不是最初的ACTION_DOWN，也就是现在是up 或者move事件了
//mFirstTouchTarget 为null说明自己没有需要处理事件的对象，也就是自己这个ViewGroup下没有View要处理事件，所以拦截
//
intercepted = true;
}
// If intercepted, start normal event dispatch. Also if there is already
// a view that is handling the gesture, do normal event dispatch.
if (intercepted || mFirstTouchTarget != null) {
ev.setTargetAccessibilityFocus(false);
}
// Check for cancelation.
//检查事件是否被取消
final boolean canceled = resetCancelNextUpFlag(this)
|| actionMasked == MotionEvent.ACTION_CANCEL;
// Update list of touch targets for pointer down, if needed.
final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0;
//定义了一个新的触摸对象，下面会用到
TouchTarget newTouchTarget = null;
boolean alreadyDispatchedToNewTouchTarget = false;
if (!canceled && !intercepted) {//没被取消或拦截
// If the event is targeting accessiiblity focus we give it to the
// view that has accessibility focus and if it does not handle it
// we clear the flag and dispatch the event to all children as usual.
// We are looking up the accessibility focused host to avoid keeping
// state since these events are very rare.
View childWithAccessibilityFocus = ev.isTargetAccessibilityFocus()
? findChildWithAccessibilityFocus() : null;
//ACTION_POINTER_DOWN 是说在有一个触摸点的情况下，又有手指触摸屏幕。多点触控的判断
//主要关心ACTION_DOWN事件就可以了，
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
final int idBitsToAssign = split ? 1 << ev.getPointerId(actionIndex)
: TouchTarget.ALL_POINTER_IDS;
// Clean up earlier touch targets for this pointer id in case they
// have become out of sync.
removePointersFromTouchTargets(idBitsToAssign);
//有效的子View的数量
final int childrenCount = mChildrenCount;
//newTouchTarget 为null且子view数量不为0
if (newTouchTarget == null && childrenCount != 0) {
final float x = ev.getX(actionIndex);
final float y = ev.getY(actionIndex);
// Find a child that can receive the event.
// Scan children from front to back.
//找到一个能接收事件的子View，视图层次上从上层到下层的顺序查找
final ArrayList<View> preorderedList = buildTouchDispatchChildList();
final boolean customOrder = preorderedList == null
&& isChildrenDrawingOrderEnabled();
final View[] children = mChildren;
//是子View倒序遍历子View，因为在添加子view到group的过程中，先添加的显示在底层，后添加的显示在上层，所以查找的时候，先从可见的上层查找起
for (int i = childrenCount - 1; i >= 0; i--) {
final int childIndex = getAndVerifyPreorderedIndex(
childrenCount, i, customOrder);
final View child = getAndVerifyPreorderedView(
preorderedList, children, childIndex);
// If there is a view that has accessibility focus we want it
// to get the event first and if not handled we will perform a
// normal dispatch. We may do a double iteration but this is
// safer given the timeframe.
//
if (childWithAccessibilityFocus != null) {
if (childWithAccessibilityFocus != child) {
continue;
}
childWithAccessibilityFocus = null;
i = childrenCount - 1;
}
//判断子View能不能收到触摸事件
//判断自VIew是不是在触摸范围内 如果不满足，就不检查了
if (!canViewReceivePointerEvents(child)
|| !isTransformedTouchPointInView(x, y, child, null)) {
ev.setTargetAccessibilityFocus(false);
continue;
}
//子View满足可触摸和在触摸范围内
//找到某一指定的子view的TouchTarget对象，传递参数有子View，返回子VIew的TouchTarget对象
newTouchTarget = getTouchTarget(child);
//没有找到子View的TouchTarget对象的处理
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;
}
resetCancelNextUpFlag(child);
//把经过一定改变的MotionEvent传递给子View的相对应的区域，是在这个方法里，进行的子View的分发事件的调用。稍后单独分析。
if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
// Child wants to receive touch within its bounds.
//返回true表示子View想处理消费事件，
mLastTouchDownTime = ev.getDownTime();
//找到消费事件的view的index
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();
//把要消费事件的子View的TouchTarget对象放到list开头
//addTouchTarget 里面对mFirstTouchTarget进行了赋值，并返回，mFirstTouchTarget和newTouchTarget 此时指向相同
newTouchTarget = addTouchTarget(child, idBitsToAssign);
//已经分发标识设置为true alreadyDispatchedToNewTouchTarget = true;
break;
}
// The accessibility focus didn't handle the event, so clear
// the flag and do a normal dispatch to all children.
ev.setTargetAccessibilityFocus(false);
}
if (preorderedList != null) preorderedList.clear();
}
//没有找到消费事件的子View
if (newTouchTarget == null && mFirstTouchTarget != null) {
// Did not find a child to receive the event.
// Assign the pointer to the least recently added target.
newTouchTarget = mFirstTouchTarget;
while (newTouchTarget.next != null) {
newTouchTarget = newTouchTarget.next;
}
newTouchTarget.pointerIdBits |= idBitsToAssign;
}
}
}
//以上是对 不拦截，未取消事件的处理和分发 ，如果找到了要消费事件的view， 那么mFirstTouchTarget 就不应该为空了
//mFirstTouchTarget 为null 一是可能事件都被拦截了，二是没有找到要消费事件的子View
// Dispatch to touch targets.
if (mFirstTouchTarget == null) {
// No touch targets so treat this as an ordinary view.
//没有触摸对象，把它当成原始的view来处理
//第三个参数传递是null，在里面判断了null会调用view的dispatchTouchEvent方法，也就是把ViewGroup当成view处理
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
} else {
//有子View消费事件
//
// Dispatch to touch targets, excluding the new touch target if we already
// dispatched to it. Cancel touch targets if necessary.
TouchTarget predecessor = null;
TouchTarget target = mFirstTouchTarget;
while (target != null) {
final TouchTarget next = target.next;
//alreadyDispatchedToNewTouchTarget为true是在找到newTouchTarget的时候设置的
//且alreadyDispatchedToNewTouchTarget设置为true是在ACTION_DOWN的if判断里面的，它消费了ACTION_DOWN事件
//所以返回handled = true表示已经有子view消费事件了
if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
handled = true;
} else {
// 对于非ACTION_DOWN事件，则继续传递给目标子组件进行处理(注意这里的非ACTION_DOWN事件已经不需要再判断是否拦截)
final boolean cancelChild = resetCancelNextUpFlag(target.child)
|| intercepted;
if (dispatchTransformedTouchEvent(ev, cancelChild,
target.child, target.pointerIdBits)) {
// 如果target子组件进行处理，符合某些条件的话，会传递ACTION_CANCEL给target子组件
// 条件是：如果ACTION_DOWN时没有被拦截，而后面的touch事件被拦截，则需要发送ACTION_CANCEL给target子组件
handled = true;
}
if (cancelChild) {
if (predecessor == null) {
mFirstTouchTarget = next;
} else {
predecessor.next = next;
}
target.recycle();
target = next;
continue;
}
}
predecessor = target;
target = next;
}
}
// Update list of touch targets for pointer up or cancel, if needed.
//ACTION_CANCEL或者ACTION_UP，重置touch 的状态
//mFirstTouchTarget重置为null
if (canceled
|| actionMasked == MotionEvent.ACTION_UP
|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
resetTouchState();
} else if (split && actionMasked == MotionEvent.ACTION_POINTER_UP) {
//多点触控的取消处理
final int actionIndex = ev.getActionIndex();
final int idBitsToRemove = 1 << ev.getPointerId(actionIndex);
removePointersFromTouchTargets(idBitsToRemove);
}
}
if (!handled && mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(ev, 1);
}
return handled;
}