Android事件分发原理分析
MotionEvent.ACTION_DOWN传递
在Android中，触碰控件的时候回产生一个ACTION_DOWN事件并逐层向下传递，首先ACTION_DOWN回先从Activity的dispatchTouchEvent方法开始向下传递：
public boolean dispatchTouchEvent(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
onUserInteraction();
}
if (getWindow().superDispatchTouchEvent(ev)) {
return true;
}
return onTouchEvent(ev);
}该方法调用了Activity中的Window的superDispatchTouchEvent方法，也就是PhoneWindow中：
@Override
public boolean superDispatchTouchEvent(MotionEvent event) {
return mDecor.superDispatchTouchEvent(event);
}然后接着调用mDecor的superDispatchTouchEvent方法，而mDecor就是我们熟悉的DecorView类的对象，是一个ViewGroup类型的，这里先大概了解一下Activity布局层级结构：
image.png
从图上可以看出，Activity实际上是包含了一个PhoneWindow，然后在PhoneWindow中又包含了DecorView的ViewGroup，我们通过setContentView为Activity设置的布局文件最终是添加到DecorView下的，也就是我们的xml布局文件最终是DecorView的child，所以当ACTION_DOWN传递到DecorView的superDispatchTouchEvent方法的时候：
public boolean superDispatchTouchEvent(MotionEvent event) {
return super.dispatchTouchEvent(event);
}实际上DecorView的superDispatchTouchEvent就是调用了ViewGroup的dispatchTouchEvent方法继续往子层级继续传递，ViewGroup的dispatchTouchEvent方法源码太长了，这里就不贴上来了，在分析到关键部分的时候只贴关键代码吧。在ViewGroup的dispatchTouchEvent方法里，首先：
// Handle an initial down.
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();
}看注释是出来初始化的ACTION_DOWN事件，为什么要这么作？我的理解是ACTION_DOWN应该作为触摸动作最先发生的事件，一个触摸动作首先发生了ACTION_DOWN事件，然后如果又移动就会发生ACTION_MOVEDMOVE事件，接着再抬手发生了ACTION_UP事件，当然如果你没抬手，只是吧触碰点移动出了控件的范围，那应该是发生ACTION_CANCEL事件（这个有些手机可能不会发生ACTION_CANCEL事件而是发生ACTION_UP事件），这才是一个完整的触摸动作，所以对于一个单点触摸动作来说ACTION_DOWN在这个动作完成之前ACTION_DOWN只会发生一次，因此这里需要吧控件之前发生的一些触摸事件留下来的touch状态信息抛出ACTION_CANCEL事件来结束，然后清空该控件的touch信息与状态恢复到ACTION_DOWN事件发生之前的状态再接着传递ACTION_DOWN事件：
/**
* Cancels and clears all touch targets.
*/
private void cancelAndClearTouchTargets(MotionEvent event) {
if (mFirstTouchTarget != null) {
boolean syntheticEvent = false;
if (event == null) {
final long now = SystemClock.uptimeMillis();
event = MotionEvent.obtain(now, now,
MotionEvent.ACTION_CANCEL, 0.0f, 0.0f, 0);
event.setSource(InputDevice.SOURCE_TOUCHSCREEN);
syntheticEvent = true;
}
for (TouchTarget target = mFirstTouchTarget; target != null; target = target.next) {
resetCancelNextUpFlag(target.child);
dispatchTransformedTouchEvent(event, true, target.child, target.pointerIdBits);
}
clearTouchTargets();
if (syntheticEvent) {
event.recycle();
}
}
}dispatchTransformedTouchEvent(event, true, target.child, target.pointerIdBits)就是把当前的ACTION_DOWN先设置成ACTION_CANCEL派发给子控件然后再恢复ACTION_DOWN状态：
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;
}清空touch信息只会，继续恢复ACTION_DOWN的传递，在ViewGroup的dispatchTouchEvent方法中，ACTION_DOWN回执行到以下代码：
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;
}ACTION_DOWN事件回满足if分支，else暂时不管，在if分支中出现了一个disallowIntercept变量，这个是控制该控件是否允许拦截touch事件用的，由ViewGroup中requestDisallowInterceptTouchEvent方法来控制：
@Override
public void requestDisallowInterceptTouchEvent(boolean disallowIntercept) {
if (disallowIntercept == ((mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0)) {
// We're already in this state, assume our ancestors are too
return;
}
if (disallowIntercept) {
mGroupFlags |= FLAG_DISALLOW_INTERCEPT;
} else {
mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT;
}
// Pass it up to our parent
if (mParent != null) {
mParent.requestDisallowInterceptTouchEvent(disallowIntercept);
}
}如果disallowIntercept为true那就是不允许拦截，于是就不会继续调用onInterceptTouchEvent方法，如果为false，就是允许拦截，onInterceptTouchEvent方法将被调用：
public boolean onInterceptTouchEvent(MotionEvent ev) {
if (ev.isFromSource(InputDevice.SOURCE_MOUSE)
&& ev.getAction() == MotionEvent.ACTION_DOWN
&& ev.isButtonPressed(MotionEvent.BUTTON_PRIMARY)
&& isOnScrollbarThumb(ev.getX(), ev.getY())) {
return true;
}
return false;
}这个方法返回true表示触摸事件要被拦截，false表示触摸事件不被拦截，可继续往下传递，如果触摸事件没有被取消或者拦截，会继续执行以下一大段代码：
if (!canceled && !intercepted) {
// 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;
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);
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;
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;
}
if (!canViewReceivePointerEvents(child)
|| !isTransformedTouchPointInView(x, y, child, null)) {
ev.setTargetAccessibilityFocus(false);
continue;
}
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;
}
resetCancelNextUpFlag(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();
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();
}
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;
}
}
}这里面的核心其实就是遍历该ViewGroup下的所有Child，如果当前的ViewGroup没有Child了，那么mFirstTouchTarget == null，接着直接执行：
// 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);
}如果ViewGroup有Child，判断Child是否有资格接收触摸事件：
/**
* Returns true if a child view can receive pointer events.
* @hide
*/
private static boolean canViewReceivePointerEvents(@NonNull View child) {
return (child.mViewFlags & VISIBILITY_MASK) == VISIBLE
|| child.getAnimation() != null;
}
/**
* Returns true if a child view contains the specified point when transformed
* into its coordinate space.
* Child must not be null.
* @hide
*/
protected boolean isTransformedTouchPointInView(float x, float y, View child,
PointF outLocalPoint) {
final float[] point = getTempPoint();
point[0] = x;
point[1] = y;
transformPointToViewLocal(point, child);
final boolean isInView = child.pointInView(point[0], point[1]);
if (isInView && outLocalPoint != null) {
outLocalPoint.set(point[0], point[1]);
}
return isInView;
}子控件必须是可见并且触摸的坐标在控件范围内才能接收触摸事件，这里有一个小细节，我么可以学习如果来把触摸的坐标点是否在控件范围内这个判断：
public boolean pointInView(float localX, float localY, float slop) {
return localX >= -slop && localY >= -slop && localX < ((mRight - mLeft) + slop) &&
localY < ((mBottom - mTop) + slop);
}注意坐标点的转化。继续来分析触摸事件ACTION_DOWN的传递，在找到能够接收ACTION_DOWN的Child之后，会执行dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)，然后根据返回值决定是否把事件继续往下一个Child传递：
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;
}如果dispatchTransformedTouchEvent返回true表示事件已经被消费，那就会直接break，事件就不会继续传递给下一个Child了，返回false的就会继续循环把事件传递给下一个Child
// 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);
}child == null的时候说明ViewGroup没有child，直接会调用到View的dispatchTouchEvent，其实就是ViewGroup本身； child != null的时候就会执行child.dispatchTouchEvent(transformedEvent)，child是View类型的，再看View的dispatchTouchEvent方法：
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();
}
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;
}
}
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;
}这里就很简单了，判断View是否是enabled的，如果是，就会触发这个View的OnTouchListener的onTouch，然后根据onTouch的返回值决定是否触发View的onTouchEvent，也就是说OnTouchListener会比onTouchEvent先执行，到这ACTION_DOWN事件传递结束，下面来总结以下传递流程与顺序：
image.png
MotionEvent.ACTION_UP的传递
上面提到，一个单点完整的触摸动作是从ACTION_DOWN开始，并以ACTION_UP或者ACTION_CANCEL结束的，ACTION_UP是在ACTION_DOWN已经发生的情况下再去基于当前View的一些特性，例如是否可点击，事件是否被消费来决定ACTION_UP是否能不能到达一些控件的，ACTION_UP依然也是从Activity的dispatchTouchEvent方法开始往下逐层传递，这边可通过对比Button和TextView对于ACTION_UP的不同处理作比较：
- Button与TextView对于ACTION_UP的区别，Buton是可点击的isClickable方法返回true，而TextView是不可点击的isClickable方法返回false，所以Button在处理ACTION_DOWN的时候，会在View的onTouchEvent返回true：
if (!result && onTouchEvent(event)) {
result = true;
}因此直接导致了View的dispatchTouchEvent方法也返回true，由此逐级继续向上返回这个true，因此Button的父控件，Activity的dispatchTouchEvent方法都会纷纷的返回true，在ViewGroup当中收到View的dispatchTouchEvent返回true的时候会执行以下代码：
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;
}因为View的dispatchTouchEvent返回true，所以也返回true，原因是dispatchTransformedTouchEvent中去分发执行了View的dispatchTouchEvent：
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);
}handled就是View的dispatchTouchEvent返回的值，表示事件已经被消费了，dispatchTransformedTouchEvent返回true之后，就执行了newTouchTarget = addTouchTarget(child, idBitsToAssign)：
private TouchTarget addTouchTarget(@NonNull View child, int pointerIdBits) {
final TouchTarget target = TouchTarget.obtain(child, pointerIdBits);
target.next = mFirstTouchTarget;
mFirstTouchTarget = target;
return target;
}把子控件赋值给了mFirstTouchTarget，如果mFirstTouchTarget不为null，当下一个事件ACTION_UP传递进入ViewGroup的时候：
// 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);
} 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;
}
}上面是ViewGroup的dispatchTouchEvent中对于mFirstTouchTarget是否为null的不同处理，对于Button来说，由于ACTION_DOWN被消费了，因此mFirstTouchTarget != null，所以会通过mFirstTouchTarget.child来把ACTION_UP继续分发给子View，前提当然是当前这个ViewGroup满足事件分发条件，例如事件未被拦截，这样ACTION_UP就能顺利的传递到子控件了，因此这就是为什么Button点击后能够收到ACTION_UP，而对于TextView而言，这里就不一样了，由于TextView是不可点击的，因此在执行View的onTouchEvent的时候会返回false，这将导致它的父控件ViewGroup的dispatchTransformedTouchEvent也返回false，所以dispatchTouchEvent返回false，因此mFirstTouchTarget并不会被初始化，即不会执行addTouchTarget方法，所以mFirstTouchTarget为null，当ACTION_UP从Activity传进ViewGroup的时候，发现mFirstTouchTarget == null，就是执行：
if (mFirstTouchTarget == null) {
// No touch targets so treat this as an ordinary view.
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
}可以看到dispatchTransformedTouchEvent的child参数（方法的第三个参数）直接传了一个null，这样将导致当前的ViewGroup无法将ACTION_UP传递给它的子控件，而是直接调用了：
if (child == null) {
handled = super.dispatchTouchEvent(transformedEvent);
}由于ViewGroup的父类是View，因此最终执行了View的dispatchTouchEvent，所以ACTION_UP就只传递到了ViewGroup，并不再往下传递，对于Activity的层级结构来说我们通过setContentView设置的布局是嵌套在DecorView中的，DecorView是一个ViewGroup，ACTION_UP是从Activity的dispatchTouchEvent传递进来的，因此ACTION_UP最终只会传递到DecorView这层，而不会传递到我们设置的布局控件了，当把TextView通过setClickable(true)设置成可点击的时候，TextView和它的父控件ViewGroup就能收到ACTION_UP事件，当把Button通过setClickable(false)，那么Button就喝TextView一样，无法收到ACTION_UP事件，下面来搞一个Demo，Demo地址：https://github.com/liuhongda/TouchEventDemo，Activity布局文件：
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.lhd.touchevent.MainActivity">
<com.lhd.touchevent.MyRelativeLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<com.lhd.touchevent.MyTextView
android:id="@+id/my_tv"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Hello World!"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<com.lhd.touchevent.MyButton
android:id="@+id/my_btn"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="button"
android:layout_below="@id/my_tv"/>
</com.lhd.touchevent.MyRelativeLayout>
</android.support.constraint.ConstraintLayout>MainActivity：
public class MainActivity extends Activity {
static final String tag = "MainActivity";
MyButton myButton;
MyTextView myTextView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
myTextView = (MyTextView) findViewById(R.id.my_tv);
myButton = (MyButton) findViewById(R.id.my_btn);
myTextView.setClickable(true);
myButton.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
Log.d(tag, "myButton onTouch:" + event);
return false;
}
});
myTextView.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
Log.d(tag, "myTextView onTouch:" + event);
return false;
}
});
Log.d(tag, "tv:" + myTextView.isClickable());
Log.d(tag, "btn:" + myButton.isClickable());
}
@Override
public boolean onTouchEvent(MotionEvent event) {
Log.d(tag, "onTouchEvent:" + event);
return super.onTouchEvent(event);
}
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
Log.d(tag, "dispatchTouchEvent:" + ev);
boolean touch = super.dispatchTouchEvent(ev);
Log.d(tag, "dispatchTouchEvent:" + touch);
return touch;
}
}MyRelativeLayout：
public class MyRelativeLayout extends RelativeLayout {
static final String tag = "MyRelativeLayout";
public MyRelativeLayout(Context context) {
super(context);
}
public MyRelativeLayout(Context context, AttributeSet attrs) {
super(context, attrs);
}
public MyRelativeLayout(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
@RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
public MyRelativeLayout(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
super(context, attrs, defStyleAttr, defStyleRes);
}
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
Log.d(tag, "dispatchTouchEvent:" + ev);
return super.dispatchTouchEvent(ev);
}
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
Log.d(tag, "onInterceptTouchEvent:" + ev.toString());
boolean touch = super.onInterceptTouchEvent(ev);
Log.d(tag, "onInterceptTouchEvent:" + touch);
return touch;
}
@Override
public boolean onTouchEvent(MotionEvent event) {
Log.d(tag, "onTouchEvent:" + event);
return super.onTouchEvent(event);
}
@Override
public void requestDisallowInterceptTouchEvent(boolean disallowIntercept) {
Log.d(tag, "requestDisallowInterceptTouchEvent");
super.requestDisallowInterceptTouchEvent(disallowIntercept);
}
}MyTextView：
public class MyTextView extends android.support.v7.widget.AppCompatTextView {
static final String tag = "MyTextView";
public MyTextView(Context context) {
super(context);
}
public MyTextView(Context context, @Nullable AttributeSet attrs) {
super(context, attrs);
}
public MyTextView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
@Override
public boolean dispatchTouchEvent(MotionEvent event) {
Log.d(tag, "dispatchTouchEvent:" + event);
return super.dispatchTouchEvent(event);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
Log.d(tag, "onTouchEvent:" + event);
boolean touch = super.onTouchEvent(event);
Log.d(tag, "touch:" + touch);
return touch;
}
@Override
public boolean isClickable() {
return super.isClickable();
}
}MyButton：
public class MyButton extends android.support.v7.widget.AppCompatButton {
static final String tag = "MyButton";
public MyButton(Context context) {
super(context);
}
public MyButton(Context context, AttributeSet attrs) {
super(context, attrs);
}
public MyButton(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
@Override
public boolean dispatchTouchEvent(MotionEvent event) {
Log.d(tag, "dispatchTouchEvent:" + event);
return super.dispatchTouchEvent(event);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
Log.d(tag, "onTouchEvent:" + event);
boolean touch = super.onTouchEvent(event);
Log.d(tag, "touch:" + touch);
return touch;
}
@Override
public boolean isClickable() {
return super.isClickable();
}
}点击TextView的ACTION_DOWN和ACTION_UP的传递结果打印：
12-06 00:10:27.258 13203-13203/? D/MainActivity: dispatchTouchEvent:MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=185.09766, y[0]=105.0, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51416868, downTime=51416868, deviceId=0, source=0x1002 }
12-06 00:10:27.258 13203-13203/? D/MyRelativeLayout: dispatchTouchEvent:MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=185.09766, y[0]=21.0, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51416868, downTime=51416868, deviceId=0, source=0x1002 }
12-06 00:10:27.258 13203-13203/? D/MyRelativeLayout: onInterceptTouchEvent:MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=185.09766, y[0]=21.0, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51416868, downTime=51416868, deviceId=0, source=0x1002 }
12-06 00:10:27.258 13203-13203/? D/MyRelativeLayout: onInterceptTouchEvent:false
12-06 00:10:27.258 13203-13203/? D/MyTextView: dispatchTouchEvent:MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=185.09766, y[0]=21.0, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51416868, downTime=51416868, deviceId=0, source=0x1002 }
12-06 00:10:27.258 13203-13203/? D/MainActivity: myTextView onTouch:MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=185.09766, y[0]=21.0, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51416868, downTime=51416868, deviceId=0, source=0x1002 }
12-06 00:10:27.259 13203-13203/? D/MyTextView: onTouchEvent:MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=185.09766, y[0]=21.0, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51416868, downTime=51416868, deviceId=0, source=0x1002 }
12-06 00:10:27.259 13203-13203/? D/MyTextView: touch:false
12-06 00:10:27.259 13203-13203/? D/MyRelativeLayout: onTouchEvent:MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=185.09766, y[0]=21.0, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51416868, downTime=51416868, deviceId=0, source=0x1002 }
12-06 00:10:27.259 13203-13203/? D/MainActivity: onTouchEvent:MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=185.09766, y[0]=105.0, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51416868, downTime=51416868, deviceId=0, source=0x1002 }
12-06 00:10:27.259 13203-13203/? D/MainActivity: dispatchTouchEvent:false
12-06 00:10:27.361 13203-13203/? D/MainActivity: dispatchTouchEvent:MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=185.09766, y[0]=105.0, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51416972, downTime=51416868, deviceId=0, source=0x1002 }
12-06 00:10:27.361 13203-13203/? D/MainActivity: onTouchEvent:MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=185.09766, y[0]=105.0, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51416972, downTime=51416868, deviceId=0, source=0x1002 }
12-06 00:10:27.361 13203-13203/? D/MainActivity: dispatchTouchEvent:false日志打印中MyTextView: touch:false是MyTextView的onTouchEvent方法里面打印的：
@Override
public boolean onTouchEvent(MotionEvent event) {
Log.d(tag, "onTouchEvent:" + event);
boolean touch = super.onTouchEvent(event);
Log.d(tag, "touch:" + touch);
return touch;
}而ACTION_UP确实只打印了MainActivity级别的，MainActivity以下的就没打印了，ACTION_UP是只传到了DecorView这一层，大家可以通过打断点的方式跟进DecorView的dispatchTouchEvent，而点击Button后ACTION_DOWN与ACTION_UP的传递：
12-06 00:16:39.884 13203-13203/com.lhd.touchevent D/MainActivity: dispatchTouchEvent:MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=205.09277, y[0]=220.07812, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51789495, downTime=51789495, deviceId=0, source=0x1002 }
12-06 00:16:39.884 13203-13203/com.lhd.touchevent D/MyRelativeLayout: dispatchTouchEvent:MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=205.09277, y[0]=136.07812, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51789495, downTime=51789495, deviceId=0, source=0x1002 }
12-06 00:16:39.884 13203-13203/com.lhd.touchevent D/MyRelativeLayout: onInterceptTouchEvent:MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=205.09277, y[0]=136.07812, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51789495, downTime=51789495, deviceId=0, source=0x1002 }
12-06 00:16:39.884 13203-13203/com.lhd.touchevent D/MyRelativeLayout: onInterceptTouchEvent:false
12-06 00:16:39.884 13203-13203/com.lhd.touchevent D/MyButton: dispatchTouchEvent:MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=205.09277, y[0]=70.078125, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51789495, downTime=51789495, deviceId=0, source=0x1002 }
12-06 00:16:39.885 13203-13203/com.lhd.touchevent D/MainActivity: myButton onTouch:MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=205.09277, y[0]=70.078125, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51789495, downTime=51789495, deviceId=0, source=0x1002 }
12-06 00:16:39.885 13203-13203/com.lhd.touchevent D/MyButton: onTouchEvent:MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=205.09277, y[0]=70.078125, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51789495, downTime=51789495, deviceId=0, source=0x1002 }
12-06 00:16:39.885 13203-13203/com.lhd.touchevent D/MyButton: touch:true
12-06 00:16:39.885 13203-13203/com.lhd.touchevent D/MainActivity: dispatchTouchEvent:true
12-06 00:16:40.004 13203-13203/com.lhd.touchevent D/MainActivity: dispatchTouchEvent:MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=205.09277, y[0]=220.07812, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51789615, downTime=51789495, deviceId=0, source=0x1002 }
12-06 00:16:40.004 13203-13203/com.lhd.touchevent D/MyRelativeLayout: dispatchTouchEvent:MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=205.09277, y[0]=136.07812, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51789615, downTime=51789495, deviceId=0, source=0x1002 }
12-06 00:16:40.004 13203-13203/com.lhd.touchevent D/MyRelativeLayout: onInterceptTouchEvent:MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=205.09277, y[0]=136.07812, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51789615, downTime=51789495, deviceId=0, source=0x1002 }
12-06 00:16:40.004 13203-13203/com.lhd.touchevent D/MyRelativeLayout: onInterceptTouchEvent:false
12-06 00:16:40.004 13203-13203/com.lhd.touchevent D/MyButton: dispatchTouchEvent:MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=205.09277, y[0]=70.078125, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51789615, downTime=51789495, deviceId=0, source=0x1002 }
12-06 00:16:40.005 13203-13203/com.lhd.touchevent D/MainActivity: myButton onTouch:MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=205.09277, y[0]=70.078125, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51789615, downTime=51789495, deviceId=0, source=0x1002 }
12-06 00:16:40.005 13203-13203/com.lhd.touchevent D/MyButton: onTouchEvent:MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=205.09277, y[0]=70.078125, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51789615, downTime=51789495, deviceId=0, source=0x1002 }
12-06 00:16:40.005 13203-13203/com.lhd.touchevent D/MyButton: touch:true
12-06 00:16:40.005 13203-13203/com.lhd.touchevent D/MainActivity: dispatchTouchEvent:trueMyButton: touch:true，这是MyButton的onTouchEvent里面的打印，而ACTION_UP确实有被MyButton以及MyRelativeLayout收到，日志证实了我们上面基于源码的分析是正确的
总结
- 事件触摸机制的几个重要的方法：
- ViewGroup中的dispatchTouchEvent方法，负责把事件分发给子View，如果没有子View，就自己处理了
- ViewGroup的onInterceptTouchEvent方法，是否拦截触摸事件，控制触摸事件的流向，true表示拦截事件，false表示不拦截
- ViewGroup的requestDisallowInterceptTouchEvent方法控制onInterceptTouchEvent是否可以拦截，如果requestDisallowInterceptTouchEvent传进去的方法参数disallowIntercept为true表示不允许拦截，false表示允许拦截
- View的dispatchTouchEvent负责把触摸事件进行处理，这里已经是触摸事件传递的终点了，不会再往下传递了，里面回去触发OnTouchListener，onTouchEvent，注意OnTouchListener会比onTouchEvent先触发，如果OnTouchListener返回true，那么事件就会被消费掉，onTouchEvent将不会被触发，对于View来说还有OnClickListener和OnLongClickListener事件，这些都是在onTouchEvent中在ACTION_UP来的时候处理判断的，因此如果OnTouchListener这里把触摸事件拦截了，那OnClickListener和OnLongClickListener事件将无法触发到
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原始发表：2017.12.06 ，如有侵权请联系 cloudcommunity@tencent.com 删除
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