1. 基础认知
1.1 屏幕的直角座标系
1.2 事件分发的对象是谁？
Touch事件：当用户触摸屏幕时（View 或 ViewGroup派生的控件），将产生Touch事件
Touch事件的相关细节（发生触摸的位置、时间等）被封装成MotionEvent对象
1.3 Touch事件的分类
-
MotionEvent.ACTION_DOWN //按下View（所有事件的开始）
-
MotionEvent.ACTION_UP //擡起View（与DOWN对应）
-
MotionEvent.ACTION_MOVE //滑动View
-
MotionEvent.ACTION_CANCEL //结束事件（非人为原因）
1.4 事件分发的本质
将点击事件（MotionEvent）传递到某个具体的View 且 处理的整个过程
1.5 事件分发的顺序
Activity -> ViewGroup -> View
1.6 事件分发过程主要的协作方法
dispatchTouchEvent() 、onInterceptTouchEvent()和onTouchEvent()
| 方法 | 作用 | 调用时机 |
| dispatchTouchEvent() | 分发touch事件 | 当touch事件能够传递到当前单位（Activity,Viewgroup,View）时，该方法就会调用 |
| onInterceptTouchEvent() | 判断是否拦截了某个事件，只存在于ViewGroup,普通的View没有此方法 | 在ViewGroup的dispatchTouchEvent()内部调用 |
| onTouchEvent() | 处理touch事件 | 在dispatchTouchEvent()内部调用 |
2. 事件机制源码分析
2.1 Activity的事件分发机制
当一个点击事件发生时，事件最先传到`Activity`的`dispatchTouchEvent()`进行事件分发
2.1.1 activity内事件机制源码分析
/**
* Called to process touch screen events. You can override this to
* intercept all touch screen events before they are dispatched to the
* window. Be sure to call this implementation for touch screen events
* that should be handled normally.
*
* @param ev The touch screen event.
*
* @return boolean Return true if this event was consumed.
*/
public boolean dispatchTouchEvent(MotionEvent ev) {
// 一般事件列开始都是DOWN事件 = 按下事件，故此处基本是true
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
//分析1
onUserInteraction();
}
//分析2
if (getWindow().superDispatchTouchEvent(ev)) {
// 若getWindow().superDispatchTouchEvent(ev)的返回true
// 则Activity.dispatchTouchEvent（）就返回true，则方法结束。即 ：该点击事件停止往下传递 & 事件传递过程结束
// 否则：继续往下调用Activity.onTouchEvent
return true;
}
//分析4
return onTouchEvent(ev);
}
/**
* 分析1：onUserInteraction()
* 作用：实现屏保功能
* 注：
* a. 该方法为空方法
* b. 当此activity在栈顶时，触屏点击按home，back，menu键等都会触发此方法
*/
public void onUserInteraction() {
}
/**
* 分析2：getWindow().superDispatchTouchEvent(ev)
*
* getWindow() = 获取Window类的对象
* Window类是抽象类，其唯一实现类 = PhoneWindow类；即此处的Window类对象 = PhoneWindow类对象
* Window类的superDispatchTouchEvent()是1个抽象方法，由子类PhoneWindow类实现
*/
@Override
public boolean superDispatchTouchEvent(MotionEvent event) {
// mDecor = 顶层View（DecorView）的实例对象
// ->> 分析3
return mDecor.superDispatchTouchEvent(event);
}
/**
* 分析3：mDecor.superDispatchTouchEvent(event)
* 属于顶层View（DecorView）,也就是一个界面中最外层的那个layout
*
* DecorView类是PhoneWindow类的一个内部类
* DecorView继承自FrameLayout，是所有界面的父类
* FrameLayout是ViewGroup的子类，故DecorView的间接父类 = ViewGroup
*/
public boolean superDispatchTouchEvent(MotionEvent event) {
// 调用父类的方法 = ViewGroup的dispatchTouchEvent()
// 即 将事件传递到ViewGroup去处理，详细请看ViewGroup的事件分发机制
return super.dispatchTouchEvent(event);
}
/**
* 分析4：Activity.onTouchEvent（）
*/
public boolean onTouchEvent(MotionEvent event) {
// 当一个点击事件未被Activity下任何一个View消费时
// 应用场景：处理发生在Window边界外的触摸事件
// ->> 分析5
if (mWindow.shouldCloseOnTouch(this, event)) {
finish();
return true;
}
return false;
// 即 只有在点击事件在Window边界外才会返回true，一般情况都返回false，分析完毕
}
/**
* 分析5：mWindow.shouldCloseOnTouch(this, event)
*/
public boolean shouldCloseOnTouch(Context context, MotionEvent event) {
// 主要是对于处理边界外点击事件的判断：是否是DOWN事件，event的座标是否在边界内等
if (mCloseOnTouchOutside && event.getAction() == MotionEvent.ACTION_DOWN
&& isOutOfBounds(context, event) && peekDecorView() != null) {
return true;
}
return false;
// 返回true：说明事件在边界外，即 消费事件
// 返回false：未消费（默认）
}
2.1.2 Activity中的事件分发流程图
2.2 ViewGroup事件的分发机制
2.1.1 ViewGroup源码分析
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
// mInputEventConsistencyVerifier是调试用的，不会理会
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.
if (ev.isTargetAccessibilityFocus() && isAccessibilityFocusedViewOrHost()) {
ev.setTargetAccessibilityFocus(false);
}
boolean handled = false;
// 第1步，是否分发该事件
// onFilterTouchEventForSecurity()表示是否要分发该触摸事件。
// 如果该View不是位于顶部，并且有设置属性使该View不在顶部时不响应触摸事件，则不分发该触摸事件，即返回false。
// 否则，则对触摸事件进行分发，即返回true。
if (onFilterTouchEventForSecurity(ev)) {
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;
// Handle an initial down.
// 第2步，检测是否需要清空目标和状态
// 如果是ACTION_DOWN(即按下事件)，则清空之前的触摸事件处理目标和状态。
// 这里的情况状态包括：
// (01) 清空mFirstTouchTarget链表，并设置mFirstTouchTarget为null。
// mFirstTouchTarget是"接受触摸事件的View"所组成的单链表
// (02) 清空mGroupFlags的FLAG_DISALLOW_INTERCEPT标记
// 如果设置了FLAG_DISALLOW_INTERCEPT，则不允许ViewGroup对触摸事件进行拦截。
// (03) 清空mPrivateFlags的PFLAG_CANCEL_NEXT_UP_EVEN标记
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.
cancelAndClearTouchTargets(ev);
resetTouchState();
}
// Check for interception.
final boolean intercepted;
//第3步，检查当前ViewGroup是否想要拦截触摸事件
//在这里通过action是否是down事件和mFirstTouchTarget != null来判断是否进行事件拦截
//mFirstTouchTarget表示处理事件的child。
//如果mFirstTouchTarget != null,表示有child正在处理事件，
//mFirstTouchTarget == null,表示没有child正在处理事件，即ViewGroup正在处理事件
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
// 检查禁止拦截标记：FLAG_DISALLOW_INTERCEPT
// 如果调用了requestDisallowInterceptTouchEvent()标记的话，则FLAG_DISALLOW_INTERCEPT会为true。
// 例如，ViewPager在处理触摸事件的时候，就会调用requestDisallowInterceptTouchEvent()
// ，禁止它的父类对触摸事件进行拦截
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;
}
// 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.
// 第4步，检查当前的触摸事件是否被取消
//
// (01) 对于ACTION_DOWN而言，mPrivateFlags的PFLAG_CANCEL_NEXT_UP_EVENT位肯定是0；因此，canceled=false。
// (02) 当前的View或ViewGroup要被从父View中detach时，PFLAG_CANCEL_NEXT_UP_EVENT就会被设为true；
// 此时，它就不再接受触摸事情。
final boolean canceled = resetCancelNextUpFlag(this)
|| actionMasked == MotionEvent.ACTION_CANCEL;
// Update list of touch targets for pointer down, if needed.
// 第5步，将触摸事件分发给"当前ViewGroup的子View和子ViewGroup"
//
// 如果触摸"没有被取消"，同时也"没有被拦截"的话，则将触摸事件分发给它的子View和子ViewGroup。
// 如果当前ViewGroup的孩子有接受触摸事件的话，则将该孩子添加到mFirstTouchTarget链表中。
final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0;
TouchTarget newTouchTarget = null;
boolean alreadyDispatchedToNewTouchTarget = false;
if (!canceled && !intercepted) {
// If the event is targeting accessibility 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;
if (actionMasked == MotionEvent.ACTION_DOWN
|| (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)
|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
// 这是获取触摸事件的序号 以及 触摸事件的id信息。
// (01) 对于ACTION_DOWN，actionIndex肯定是0
// (02) 而getPointerId()是获取的该触摸事件的id，并将该id信息保存到idBitsToAssign中。
// 这个触摸事件的id是为多指触摸而添加的；对於单指触摸，getActionIndex()返回的肯定是0；
// 而对于多指触摸，第一个手指的id是0，第二个手指的id是1，第三个手指的id是2，...依次类推。
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.
// 清空这个手指之前的TouchTarget链表。
// 一个TouchTarget，相当于一个可以被触摸的对象；它中记录了接受触摸事件的View
removePointersFromTouchTargets(idBitsToAssign);
final int childrenCount = mChildrenCount;
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.
final ArrayList<View> preorderedList = buildTouchDispatchChildList();
final boolean customOrder = preorderedList == null
&& isChildrenDrawingOrderEnabled();
final View[] children = mChildren;
// 获取该ViewGroup包含的View和ViewGroup的数目，
// 然后递归遍历ViewGroup的孩子，对触摸事件进行分发。
// 递归遍历ViewGroup的孩子：是指对于当前ViewGroup的所有孩子，都会逐个遍历，并分发触摸事件；
// 对于逐个遍历到的每一个孩子，若该孩子是ViewGroup类型的话，则会递归到调用该孩子的孩子，...
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;
}
// 如果child可以接受触摸事件，
// 并且触摸座标(x,y)在child的可视范围之内的话；
// 则继续往下执行。否则，调用continue。
// child可接受触摸事件：是指child的是可见的(VISIBLE)；或者虽然不可见，但是位于动画状态。
if (!canViewReceivePointerEvents(child)
|| !isTransformedTouchPointInView(x, y, child, null)) {
ev.setTargetAccessibilityFocus(false);
continue;
}
// getTouchTarget()的作用是查找child是否存在于mFirstTouchTarget的单链表中。
// 是的话，返回对应的TouchTarget对象；否则，返回null。
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;
}
// 重置child的mPrivateFlags变量中的PFLAG_CANCEL_NEXT_UP_EVENT位。
resetCancelNextUpFlag(child);
// 调用dispatchTransformedTouchEvent()将触摸事件分发给child。
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();
// 如果child能够接受该触摸事件，即child消费或者拦截了该触摸事件的话；
// 则调用addTouchTarget()将child添加到mFirstTouchTarget链表的表头，并返回表头对应的TouchTarget
// 同时还设置alreadyDispatchedToNewTouchTarget为true。
newTouchTarget = addTouchTarget(child, idBitsToAssign);
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();
}
// 如果newTouchTarget为null，并且mFirstTouchTarget不为null；
// 则设置newTouchTarget为mFirstTouchTarget链表中第一个不为空的节点。
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;
}
}
}
// Dispatch to touch targets.
// 第6步，进一步的对触摸事件进行分发
//
// (01) 如果mFirstTouchTarget为null，意味着还没有任何View来接受该触摸事件；
// 此时，将当前ViewGroup看作一个View；
// 将会调用"当前的ViewGroup的父类View的dispatchTouchEvent()"对触摸事件进行分发处理。
// 即，会将触摸事件交给当前ViewGroup的onTouch(), onTouchEvent()进行处理。
// (02) 如果mFirstTouchTarget不为null，意味着有ViewGroup的子View或子ViewGroup中，
// 有可以接受触摸事件的。那么，就将触摸事件分发给这些可以接受触摸事件的子View或子ViewGroup。
if (mFirstTouchTarget == null) {
// No touch targets so treat this as an ordinary view.
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
} else {
// 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;
if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
handled = true;
} else {
final boolean cancelChild = resetCancelNextUpFlag(target.child)
|| intercepted;
if (dispatchTransformedTouchEvent(ev, cancelChild,
target.child, target.pointerIdBits)) {
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.
// 第7步：再次检查取消标记，并进行相应的处理
if (canceled
|| actionMasked == MotionEvent.ACTION_UP
|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
resetTouchState();
} else if (split && actionMasked == MotionEvent.ACTION_POINTER_UP) {
final int actionIndex = ev.getActionIndex();
final int idBitsToRemove = 1 << ev.getPointerId(actionIndex);
removePointersFromTouchTargets(idBitsToRemove);
}
}
// mInputEventConsistencyVerifier是调试用的，不会理会
if (!handled && mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(ev, 1);
}
return handled;
}
注意：第5步，即ViewGroup尝试将触摸事件分发给它的孩子。这只有在ACTION_DOWN的时候才发生。如果它的孩子接受了触摸事件，则会调用addTouchTarget()将该孩子添加到mFirstTouchTarget链表中。 在ACTION_DOWN之后，传递ACTION_MOVE或ACTION_UP时，ViewGroup不会再执行第5步；而是在第6步中，直接遍历mFirstTouchTarget链表，查找之前接受ACTION_DOWN的孩子，并将触摸事件分配给这些孩子。
也就是说，如果ViewGroup的某个孩子没有接受ACTION_DOWN事件；那么，ACTION_MOVE和ACTION_UP等事件也一定不会分发给这个孩子！
/**
* Transforms a motion event into the coordinate space of a particular child view,
* filters out irrelevant pointer ids, and overrides its action if necessary.
* If child is null, assumes the MotionEvent will be sent to this ViewGroup instead.
*/
private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,
View child, int desiredPointerIdBits) {
final boolean handled;
// Canceling motions is a special case. We don't need to perform any transformations
// or filtering. The important part is the action, not the contents.
// 检测是否需要发送ACTION_CANCEL。
// 如果cancel为true 或者 action是ACTION_CANCEL;
// 则设置消息为ACTION_CANCEL，并将ACTION_CANCEL消息分发给对应的对象，并返回。
// (01) 如果child是空，则将ACTION_CANCEL消息分发给当前ViewGroup；
// 只不过会将ViewGroup看作它的父类View，调用View的dispatchTouchEvent()接口。
// (02) 如果child不是空，调用child的dispatchTouchEvent()。
final int oldAction = event.getAction();
if (cancel || oldAction == MotionEvent.ACTION_CANCEL) {
event.setAction(MotionEvent.ACTION_CANCEL);
if (child == null) {
handled = super.dispatchTouchEvent(event);
} else {
handled = child.dispatchTouchEvent(event);
}
event.setAction(oldAction);
return handled;
}
// Calculate the number of pointers to deliver.
final int oldPointerIdBits = event.getPointerIdBits();
final int newPointerIdBits = oldPointerIdBits & desiredPointerIdBits;
// If for some reason we ended up in an inconsistent state where it looks like we
// might produce a motion event with no pointers in it, then drop the event.
if (newPointerIdBits == 0) {
return false;
}
// If the number of pointers is the same and we don't need to perform any fancy
// irreversible transformations, then we can reuse the motion event for this
// dispatch as long as we are careful to revert any changes we make.
// Otherwise we need to make a copy.
final MotionEvent transformedEvent;
if (newPointerIdBits == oldPointerIdBits) {
if (child == null || child.hasIdentityMatrix()) {
if (child == null) {
handled = super.dispatchTouchEvent(event);
} else {
final float offsetX = mScrollX - child.mLeft;
final float offsetY = mScrollY - child.mTop;
event.offsetLocation(offsetX, offsetY);
handled = child.dispatchTouchEvent(event);
event.offsetLocation(-offsetX, -offsetY);
}
return handled;
}
transformedEvent = MotionEvent.obtain(event);
} else {
transformedEvent = event.split(newPointerIdBits);
}
// Perform any necessary transformations and dispatch.
// (01) 如果child是空，则将ViewGroup看作它的父类View，调用View的dispatchTouchEvent()接口。
// (02) 如果child不是空，调用child的dispatchTouchEvent()。
if (child == null) {
handled = super.dispatchTouchEvent(transformedEvent);
} else {
final float offsetX = mScrollX - child.mLeft;
final float offsetY = mScrollY - child.mTop;
transformedEvent.offsetLocation(offsetX, offsetY);
if (! child.hasIdentityMatrix()) {
transformedEvent.transform(child.getInverseMatrix());
}
handled = child.dispatchTouchEvent(transformedEvent);
}
// Done.
transformedEvent.recycle();
return handled;
}
说明：dispatchTransformedTouchEvent()会对触摸事件进行重新打包后再分发。
如果它的第三个参数child是null，则会将触摸消息分发给ViewGroup自己，只不过此时是将ViewGroup看作一个View，即调用View的dispatchTouchEvent()进行消息分发。而View的dispatchTouchEvent()会将触摸事件分发给onTouch(), onTouchEvent()进行处理。 如果它的第三个参数child不是null，则会调用child.dispatchTouchEvent()进行消息分发。而如果这个child是ViewGroup对象的话，它则又会递归的将消息分发给它的孩子。
2.2.2 ViewGroup中的事件分发流程图
2.3 View事件的分发机制
2.3.1 View源码分析
/**
* 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 the event should be handled by accessibility focus first.
if (event.isTargetAccessibilityFocus()) {
// We don't have focus or no virtual descendant has it, do not handle the event.
if (!isAccessibilityFocusedViewOrHost()) {
return false;
}
// We have focus and got the event, then use normal event dispatch.
event.setTargetAccessibilityFocus(false);
}
boolean result = false;
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onTouchEvent(event, 0);
}
final int actionMasked = event.getActionMasked();
if (actionMasked == MotionEvent.ACTION_DOWN) {
// Defensive cleanup for new gesture
stopNestedScroll();
}
// 如果该View被遮蔽，并且该View在被遮蔽时不响应点击事件；
// 此时，返回false；不会执行onTouch()或onTouchEvent()，即过滤调用该点击事件。
// 否则，返回true。
// 被遮蔽的意思是：该View不是位于顶部，有其他的View在它之上。
if (onFilterTouchEventForSecurity(event)) {
if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {
result = true;
}
//noinspection SimplifiableIfStatement
ListenerInfo li = mListenerInfo;
//当这个view的onClickListener不为空且回调函数onTouch(this, event)返回true的时候，View.dispatchTouchEvent(MotionEvent event)就返回true
if (li != null && li.mOnTouchListener != null
&& (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnTouchListener.onTouch(this, event)) {
result = true;
}
//然后如果前面事件没有被消费，如果onTouchEvent(event)返回true,则View.dispatchTouchEvent(MotionEvent event)也返回true
if (!result && onTouchEvent(event)) {
result = true;
}
}
if (!result && mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(event, 0);
}
// Clean up after nested scrolls if this is the end of a gesture;
// also cancel it if we tried an ACTION_DOWN but we didn't want the rest
// of the gesture.
if (actionMasked == MotionEvent.ACTION_UP ||
actionMasked == MotionEvent.ACTION_CANCEL ||
(actionMasked == MotionEvent.ACTION_DOWN && !result)) {
stopNestedScroll();
}
return result;
}
boolean isAccessibilityFocusedViewOrHost() {
return isAccessibilityFocused() || (getViewRootImpl() != null && getViewRootImpl()
.getAccessibilityFocusedHost() == this);
}
注意：
1.View中的dispatchTouchEvent()会将事件传递给"自己的onTouch()", "自己的onTouchEvent()"进行处理。而且onTouch()的优先级比onTouchEvent()的优先级要高。
2. onTouch()与onTouchEvent()都是View中用户处理触摸事件的API。onTouch是OnTouchListener接口中的函数，OnTouchListener接口需要用户自己实现。onTouchEvent()是View自带的接口，Android系统提供了默认的实现；当然，用户可以重载该API。
3. onTouch()与onTouchEvent()有两个不同之处：(01), onTouch()是View提供给用户，让用户自己处理触摸事件的接口。而onTouchEvent()是Android系统自己实现的接口。(02)，onTouch()的优先级比onTouchEvent()的优先级更高。dispatchTouchEvent()中分发事件的时候，会先将事件分配给onTouch()进行处理，然后才分配给onTouchEvent()进行处理。 如果onTouch()对触摸事件进行了处理，并且返回true；那么，该触摸事件就不会分配在分配给onTouchEvent()进行处理了。只有当onTouch()没有处理，或者处理了但返回false时，才会分配给onTouchEvent()进行处理。
/**
* Implement this method to handle touch screen motion events.
* <p>
* If this method is used to detect click actions, it is recommended that
* the actions be performed by implementing and calling
* {@link #performClick()}. This will ensure consistent system behavior,
* including:
* <ul>
* <li>obeying click sound preferences
* <li>dispatching OnClickListener calls
* <li>handling {@link AccessibilityNodeInfo#ACTION_CLICK ACTION_CLICK} when
* accessibility features are enabled
* </ul>
*
* @param event The motion event.
* @return True if the event was handled, false otherwise.
*/
public boolean onTouchEvent(MotionEvent event) {
final float x = event.getX();
final float y = event.getY();
final int viewFlags = mViewFlags;
final int action = event.getAction();
final boolean clickable = ((viewFlags & CLICKABLE) == CLICKABLE
|| (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)
|| (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE;
if ((viewFlags & ENABLED_MASK) == DISABLED) {
if (action == MotionEvent.ACTION_UP && (mPrivateFlags & PFLAG_PRESSED) != 0) {
setPressed(false);
}
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
// A disabled view that is clickable still consumes the touch
// events, it just doesn't respond to them.
return clickable;
}
// 如果该View的mTouchDelegate不为null的话，将触摸消息分发给mTouchDelegate。
// mTouchDelegate的默认值是null。
if (mTouchDelegate != null) {
if (mTouchDelegate.onTouchEvent(event)) {
return true;
}
}
// 如果View可以被点击的话，则执行if里面的内容。
// 这其中涉及到的主要是获取焦点，设置按下状态，触发onClick(), onLongClick()事件等等。
if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {
switch (action) {
case MotionEvent.ACTION_UP:
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
if ((viewFlags & TOOLTIP) == TOOLTIP) {
handleTooltipUp();
}
if (!clickable) {
removeTapCallback();
removeLongPressCallback();
mInContextButtonPress = false;
mHasPerformedLongPress = false;
mIgnoreNextUpEvent = false;
break;
}
boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0;
if ((mPrivateFlags & PFLAG_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 (prepressed) {
// The button is being released before we actually
// showed it as pressed. Make it show the pressed
// state now (before scheduling the click) to ensure
// the user sees it.
setPressed(true, x, y);
}
if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) {
// 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)) {
performClickInternal();
}
}
}
if (mUnsetPressedState == null) {
mUnsetPressedState = new UnsetPressedState();
}
if (prepressed) {
postDelayed(mUnsetPressedState,
ViewConfiguration.getPressedStateDuration());
} else if (!post(mUnsetPressedState)) {
// If the post failed, unpress right now
mUnsetPressedState.run();
}
removeTapCallback();
}
mIgnoreNextUpEvent = false;
break;
case MotionEvent.ACTION_DOWN:
if (event.getSource() == InputDevice.SOURCE_TOUCHSCREEN) {
mPrivateFlags3 |= PFLAG3_FINGER_DOWN;
}
mHasPerformedLongPress = false;
if (!clickable) {
checkForLongClick(0, x, y);
break;
}
if (performButtonActionOnTouchDown(event)) {
break;
}
// Walk up the hierarchy to determine if we're inside a scrolling container.
boolean isInScrollingContainer = isInScrollingContainer();
// For views inside a scrolling container, delay the pressed feedback for
// a short period in case this is a scroll.
if (isInScrollingContainer) {
mPrivateFlags |= PFLAG_PREPRESSED;
if (mPendingCheckForTap == null) {
mPendingCheckForTap = new CheckForTap();
}
mPendingCheckForTap.x = event.getX();
mPendingCheckForTap.y = event.getY();
postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());
} else {
// Not inside a scrolling container, so show the feedback right away
setPressed(true, x, y);
checkForLongClick(0, x, y);
}
break;
case MotionEvent.ACTION_CANCEL:
if (clickable) {
setPressed(false);
}
removeTapCallback();
removeLongPressCallback();
mInContextButtonPress = false;
mHasPerformedLongPress = false;
mIgnoreNextUpEvent = false;
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
break;
case MotionEvent.ACTION_MOVE:
if (clickable) {
drawableHotspotChanged(x, y);
}
// Be lenient about moving outside of buttons
if (!pointInView(x, y, mTouchSlop)) {
// Outside button
// Remove any future long press/tap checks
removeTapCallback();
removeLongPressCallback();
if ((mPrivateFlags & PFLAG_PRESSED) != 0) {
setPressed(false);
}
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
}
break;
}
return true;
}
return false;
}
2.3.1 View的事件分发流程图
