Android中view的onTouch&onClick事件分发机制详解

当view设置了setOnClickListener或setOnTouchListener之后，onClick或onTouch方法才会被调用，如下

mTextView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Logger.d(MainActivity.class," onClick");
}
});

mTextView.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
Logger.d(MainActivity.class," onTouch event :"+event.getAction());
return false;
}
});

log如下：



使用自定义MyTextView，继承TextView并重写dispatchTouchEvent和onTouchEvent，log如下：



从log看调用顺序依次为（如果手没有抖，可能没有ACTION_MOVE事件）

ACTION_DOWN:MainActivity@dispatchTouchEvent,MyTextView@dispatchTouchEvent,MainActivity@onTouch，MyTextView@onTouchEvent

ACTION_MOVE:MainActivity@dispatchTouchEvent,MyTextView@dispatchTouchEvent,MainActivity@onTouch,MyTextView@onTouchEvent

ACTION_UP:MainActivity@dispatchTouchEvent,MyTextView@dispatchTouchEvent,MainActivity@onTouch,MyTextView@onTouchEvent

当MyTextView@onTouchEvent的event.getAction()为

MotionEvent.ACTION_UP时才调用onClick

注：单手或双手操作触摸屏幕事件，一般会有下面几种

单手指操作：ACTION_DOWN(0) ACTION_MOVE(2) ACTION_UP(1)

多手指操作：ACTION_DOWN ACTION_POINTER_DOWN(5) ACTION_MOVE ACTION_POINTER_UP(6) ACTION_UP.

从上面的log可以看出是先执行TextView设置的onTouch，再调用对应的onClick方法的，Activity和控件都是先执行dispatchTouchEvent来分发touchEvent，下面我们来从源码的角度，看下这个是怎么实现的

frameworks/base/core/java/android/app/Activity.java
public boolean dispatchTouchEvent(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_DOWN){
onUserInteraction();
}
if (getWindow().superDispatchTouchEvent(ev)) {
return true;
}
return onTouchEvent(ev);
}
public void onUserInteraction() {
}

通过上面的方法可以看出，onUserInteraction方法在有当前activity捕获到touchEvent的ACTION_DOWN事件时，会被触发这个方法，说到了onUserInteraction，我们顺便看看和它相关联的一个方法onUserLeaveHint

onUserLeaveHint：当用户按下 Home键，Activity#onUserLeaveHint()将会被回调。但是当来电导致来电activity自动占据前台，Activity#onUserLeaveHint()将不会被回调。

onUserInteraction：当前activity有key, touch, or trackball event事件时都会调用，经常和onUserLeaveHint一起用来管理通知的。

接下来会调用getWindow().superDispatchTouchEvent(ev)，把touchEvent派遣给PhoneWindow（getWindow()返回的是Window的实例，而PhoneWindow是Window唯一的孩子）

frameworks/base/core/java/com/android/internal/policy/PhoneWindow.java
@Override
public boolean superDispatchKeyEvent(KeyEvent event) {
return mDecor.superDispatchKeyEvent(event);
}

在PhoneWindow里继续把事件传递给DecorView，从前一篇setContentView详解中，我们知道了DecorView是所有视图的根视图，接下来看看DecorView里的superDispatchKeyEvent

frameworks/base/core/java/com/android/internal/policy/DecorView.java
public boolean superDispatchKeyEvent(KeyEvent event) {
// Give priority to closing action modes if applicable.
if (event.getKeyCode() == KeyEvent.KEYCODE_BACK) {
final int action = event.getAction();
// Back cancels action modes first.
if (mPrimaryActionMode != null) {
if (action == KeyEvent.ACTION_UP) {
mPrimaryActionMode.finish();
}
return true;
}
}
return super.dispatchKeyEvent(event);
}

最后调用了父类的dispatchKeyEvent的，接着看看父类FrameLayout.java的dispatchKeyEvent，FrameLayout里没有定义这个方法，dispatchKeyEvent是从FrameLayout的父类ViewGroup.java里获取来，我们直接看这个方法

frameworks/base/core/java/android/view/ViewGroup.java
public boolean dispatchTouchEvent(MotionEvent ev) {
...
boolean handled = false;
if (onFilterTouchEventForSecurity(ev)) {
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;

...
// Check for interception.
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;
}

// 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.
final boolean canceled = resetCancelNextUpFlag(this)
|| actionMasked == MotionEvent.ACTION_CANCEL;
...
TouchTarget newTouchTarget = null;
boolean alreadyDispatchedToNewTouchTarget = false;
if (!canceled && !intercepted) {
...
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;
for (int i = childrenCount - 1; i >= 0; i--) {
final int childIndex = getAndVerifyPreorderedIndex(
childrenCount, i, customOrder);
final View child = getAndVerifyPreorderedView(
preorderedList, children, childIndex);
// Dispatch to touch targets.
if (mFirstTouchTarget == null) {
// No touch targets so treat this as an ordinary view.
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
}

return handled;
}

在这个方法里会依次调用onInterceptTouchEvent，获取actionMasked是否为ACTION_CANCEL判断是否中断或取消事件的传递，通过buildTouchDispatchChildList来获取自定义排序的视图，对应的touchEvent将会被dispatch，通过dispatchTransformedTouchEvent把事件传递到对应view上

private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,
View child, int desiredPointerIdBits) {
final boolean handled;

...
// 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.
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;
}

这样自定义的MyTextView中的dispatchTouchEvent就会被调用,这个方法是定义在View.java里的，下面来看看具体实现

frameworks/base/core/java/android/view/View.java
public boolean dispatchTouchEvent(MotionEvent event) {
...
if (onFilterTouchEventForSecurity(event)) {
if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {
result = true;
}
//noinspection SimplifiableIfStatement
ListenerInfo li = mListenerInfo;
if (li != null && li.mOnTouchListener != null
&& (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnTouchListener.onTouch(this, event)) {
result = true;
}

if (!result && onTouchEvent(event)) {
result = true;
}
}
...
return result;
}

boolean isAccessibilityFocusedViewOrHost() {
return isAccessibilityFocused() || (getViewRootImpl() != null && getViewRootImpl()
.getAccessibilityFocusedHost() == this);
}

在这个方法里面会先判断当前view的OnTouchListener是否为null，当前view是否为enabled以及mOnTouchListener.onTouch返回的结果来决定result的值，紧接着下面就用这个值来判断是否需要调用view的onTouchEvent方法，只有当result为false时，

onTouchEvent才会被调用，那么onclick是在那被调用的呢，跟进去看看onTouchEvent的定义

frameworks/base/core/java/android/view/View.java
public boolean onTouchEvent(MotionEvent event) {
final float x = event.getX();
final float y = event.getY();
final int viewFlags = mViewFlags;
final int action = event.getAction();

if ((viewFlags & ENABLED_MASK) == DISABLED) {
if (action == MotionEvent.ACTION_UP && (mPrivateFlags & PFLAG_PRESSED) != 0) {
setPressed(false);
}
// 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)
|| (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE);
}
if (mTouchDelegate != null) {
if (mTouchDelegate.onTouchEvent(event)) {
return true;
}
}

if (((viewFlags & CLICKABLE) == CLICKABLE ||
(viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) ||
(viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE) {
switch (action) {
case MotionEvent.ACTION_UP:
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)) {
performClick();
}
}
}
...
}
return true;
}
return false;
}

当touchEvent的type为ACTION_UP时，里面会调用performClick，进而在这个里面调用注册的click监听

frameworks/base/core/java/android/view/View.java
public boolean performClick() {
final boolean result;
final ListenerInfo li = mListenerInfo;
if (li != null && li.mOnClickListener != null) {
playSoundEffect(SoundEffectConstants.CLICK);
li.mOnClickListener.onClick(this);
result = true;
} else {
result = false;
}

sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
return result;
}

这样我们就知道了OnClickListener和OnTouchListener的具体调用流程，以及onClick是在onTouch方法之后调用的，只有onTouch返回false时，onTouchEvent才会被调用，并且在onTouchEvent的getAction为ACTION_UP时调用performClick，处理OnClickListener，回调onClick方法。

另外需要注意的是，如果我们重写View@onTouchEvent返回false时，当前view的dispatchTouchEvent、 onTouchEvent，以及注册的onTouch事件只会在onTouchEvent的getAction为ACTION_DOWN时被调用一次，ACTION_MOVE和ACTION_UP事件都不会被调用



从上面log看MyTextView@dispatchTouchEvent和

MyTextView@onTouchEvent只在ACTION_DOWN时执行来一次，其实View@onTouchEvent里根据 switch（action）里每次都默认返回里true,这样对应的ACTION_MOVE和ACTION_UP才会被调用

frameworks/base/core/java/android/view/View.java
public boolean onTouchEvent(MotionEvent event) {
...
if (((viewFlags & CLICKABLE) == CLICKABLE ||
(viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) ||
(viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE) {
switch (action) {
case MotionEvent.ACTION_UP:
...
break;
case MotionEvent.ACTION_DOWN:
...
break;
case MotionEvent.ACTION_CANCEL:
...
break;
case MotionEvent.ACTION_MOVE:
...
break;
}
return true;
}
return false;
}