根据View的事件机制,再添加在代码中添加一个自定义的LinearLayout,继承LinearLayout，然后复写了与事件分发机制有关的方法，日志输出
import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.widget.LinearLayout;
public class MyLinearLayout extends LinearLayout {
private static final String TAG = "MyLinearLayout";
public MyLinearLayout(Context context) {
super(context);
}
public MyLinearLayout(Context context, AttributeSet attrs) {
super(context, attrs);
}
public MyLinearLayout(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
int action = ev.getAction();
switch (action) {
case MotionEvent.ACTION_DOWN:
Log.e(TAG, "dispatchTouchEvent ACTION_DOWN");
break;
case MotionEvent.ACTION_MOVE:
Log.e(TAG, "dispatchTouchEvent ACTION_MOVE");
break;
case MotionEvent.ACTION_UP:
Log.e(TAG, "dispatchTouchEvent ACTION_UP");
break;
default:
break;
}
return super.dispatchTouchEvent(ev);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
int action = event.getAction();
switch (action) {
case MotionEvent.ACTION_DOWN:
Log.e(TAG, "onTouchEvent ACTION_DOWN");
break;
case MotionEvent.ACTION_MOVE:
Log.e(TAG, "onTouchEvent ACTION_MOVE");
break;
case MotionEvent.ACTION_UP:
Log.e(TAG, "onTouchEvent ACTION_UP");
break;
default:
break;
}
return super.onTouchEvent(event);
}
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
int action = ev.getAction();
switch (action) {
case MotionEvent.ACTION_DOWN:
Log.e(TAG, "onInterceptTouchEvent ACTION_DOWN");
break;
case MotionEvent.ACTION_MOVE:
Log.e(TAG, "onInterceptTouchEvent ACTION_MOVE");
break;
case MotionEvent.ACTION_UP:
Log.e(TAG, "onInterceptTouchEvent ACTION_UP");
break;
default:
break;
}
return super.onInterceptTouchEvent(ev);
}
@Override
public void requestDisallowInterceptTouchEvent(boolean disallowIntercept) {
super.requestDisallowInterceptTouchEvent(disallowIntercept);
Log.e(TAG, "requestDisallowInterceptTouchEvent ");
}
}
<?xml version="1.0" encoding="utf-8"?>
<com.loaderman.eventanalysis.MyLinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center"
tools:context="com.jcf.eventanalysis.MainActivity">
<com.loaderman.eventanalysis.MyButton
android:id="@+id/btn"
android:layout_width="200dp"
android:layout_height="100dp"
android:text="MyButton"/>
</com.loaderman.eventanalysis.MyLinearLayout>
MyLinearLayout中包含一个MyButton，MyButton是自定义Button，然后MainActivity就是直接加载布局,直接运行代码，然后点击我们的Button，如果没有MOVE一下，就不会触发MOVE事件，看一下日志的输出：
可以看到大体的事件流程为：
MyLinearLayout的dispatchTouchEvent -> MyLinearLayout的onInterceptTouchEvent -> MyButton的dispatchTouchEvent ->Mybutton的onTouchEvent
可以看出，在View上触发事件，最先捕获到事件的为View所在的ViewGroup，然后才会到View自身~
源码分析
ViewGroup - dispatchTouchEvent
源码分析
ViewGroup - dispatchTouchEvent
________________________________________ public boolean dispatchTouchEvent(MotionEvent ev) {
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;
if (onFilterTouchEventForSecurity(ev)) {
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;
// 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();
}
// 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;
// Update list of touch targets for pointer down, if needed.
final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0;
TouchTarget newTouchTarget = null;
boolean alreadyDispatchedToNewTouchTarget = false;
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;
}
}
}
// 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;
}
}
// Update list of touch targets for pointer up or cancel, if needed.
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);
}
}
if (!handled && mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(ev, 1);
}
return handled;
}
ATION_DOWN的处理流程:
取消TouchTarget,重置TouchState的状态
cancelAndClearTouchTargets(ev); resetTouchState();
进行判断是否拦截
// 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;
}
两种可能会进入IF代码段
1、当前不允许拦截，即disallowIntercept =true，
2、当前允许拦截但是不拦截，即disallowIntercept =false,但是onInterceptTouchEvent(ev)返回false ;
注：disallowIntercept 可以通过viewGroup.requestDisallowInterceptTouchEvent(boolean);进行设置，而onInterceptTouchEvent(ev)可以进行复写。
接下来开始遍历所有的子View
进行判断当前的x,y坐标是否落在子View身上，如果在执行child.dispatchTouchEvent(ev)，就进入了View的dispatchTouchEvent代码中了，当child.dispatchTouchEvent(ev)返回true，则为mMotionTarget=child;然后return true;
小结：ViewGroup实现捕获到DOWN事件，如果代码中不做TOUCH事件拦截，则开始查找当前x,y是否在某个子View的区域内，如果在，则把事件分发下去。
把ACTION_DOWN时赋值的mMotionTarget，付给target ;
23行：if (!disallowIntercept && onInterceptTouchEvent(ev)) 当前允许拦截且拦截了，才进入IF体，当然了默认是不会拦截的~这里执行了onInterceptTouchEvent(ev)
28-30行：把坐标系统转化为子View的坐标系统
32行：直接return target.dispatchTouchEvent(ev);
可以看到，正常流程下，ACTION_MOVE在检测完是否拦截以后，直接调用了子View.dispatchTouchEvent，事件分发下去；
最后就是ACTION_UP了
17行：判断当前是否是ACTION_UP
21，28行：分别重置拦截标志位以及将DOWN赋值的mMotionTarget置为null，都UP了，当然置为null，下一次DOWN还会再赋值的~
最后，修改坐标系统，然后调用target.dispatchTouchEvent(ev);
正常情况下，整个代码的流程：
1、ACTION_DOWN中，ViewGroup捕获到事件，然后判断是否拦截，如果没有拦截，则找到包含当前x,y坐标的子View，赋值给mMotionTarget，然后调用 mMotionTarget.dispatchTouchEvent
2、ACTION_MOVE中，ViewGroup捕获到事件，然后判断是否拦截，如果没有拦截，则直接调用mMotionTarget.dispatchTouchEvent(ev)
3、ACTION_UP中，ViewGroup捕获到事件，然后判断是否拦截，如果没有拦截，则直接调用mMotionTarget.dispatchTouchEvent(ev)
当然了在分发之前都会修改下坐标系统，把当前的x，y分别减去child.left 和 child.top ，然后传给child;
关于拦截
如何拦截
上面的总结都是基于：如果没有拦截；那么如何拦截呢？
复写ViewGroup的onInterceptTouchEvent方法：
public boolean onInterceptTouchEvent(MotionEvent ev) {
int action = ev.getAction();
switch (action) {
case MotionEvent.ACTION_DOWN:
Log.e(TAG, "onInterceptTouchEvent ACTION_DOWN");
//如果你觉得需要拦截,return true
break;
case MotionEvent.ACTION_MOVE:
Log.e(TAG, "onInterceptTouchEvent ACTION_MOVE");
//如果你觉得需要拦截,return true
break;
case MotionEvent.ACTION_UP:
Log.e(TAG, "onInterceptTouchEvent ACTION_UP");
//如果你觉得需要拦截,return true
break;
default:
break;
}
return false;
}
默认是不拦截的，即返回false；如果你需要拦截，只要return true就行了，这要该事件就不会往子View传递了，并且如果你在DOWN retrun true ，则DOWN,MOVE,UP子View都不会捕获事件；如果你在MOVE return true , 则子View在MOVE和UP都不会捕获事件。
原因很简单，当onInterceptTouchEvent(ev) return true的时候，会把mMotionTarget 置为null ;
如何不被拦截
如果ViewGroup的onInterceptTouchEvent(ev) 当ACTION_MOVE时return true ，即拦截了子View的MOVE以及UP事件；
此时子View希望依然能够响应MOVE和UP时该咋办呢？
Android给我们提供了一个方法：requestDisallowInterceptTouchEvent(boolean) 用于设置是否允许拦截，我们在子View的dispatchTouchEvent中直接这么写：
@Override
public boolean dispatchTouchEvent(MotionEvent event) {
int action = event.getAction();
getParent().requestDisallowInterceptTouchEvent(true);
switch (action)
{
case MotionEvent.ACTION_DOWN:
Log.e(TAG, "dispatchTouchEvent ACTION_DOWN");
break;
case MotionEvent.ACTION_MOVE:
Log.e(TAG, "dispatchTouchEvent ACTION_MOVE");
break;
case MotionEvent.ACTION_UP:
Log.e(TAG, "dispatchTouchEvent ACTION_UP");
break;
default:
break;
}
return super.dispatchTouchEvent(event);
}
getParent().requestDisallowInterceptTouchEvent(true); 这样即使ViewGroup在MOVE的时候return true，子View依然可以捕获到MOVE以及UP事件。
注：如果ViewGroup在onInterceptTouchEvent(ev) ACTION_DOWN里面直接return true了，那么子View是没有办法的捕获事件的
如果没有找到合适的子View
我们的实例，直接点击ViewGroup内的按钮，当然直接很顺利的走完整个流程；
但是有两种特殊情况
1、ACTION_DOWN的时候，子View.dispatchTouchEvent(ev)返回的为false ;
如果你仔细看了，你会注意到ViewGroup的dispatchTouchEvent(ev)的ACTION_DOWN代码是这样的
if (child.dispatchTouchEvent(ev)) {
// Event handled, we have a target now.
mMotionTarget = child;
return true;
}
有在child.dispatchTouchEvent(ev)返回true了，才会认为找到了能够处理当前事件的View，即mMotionTarget = child;
但是如果返回false,那么mMotionTarget 依然是null
mMotionTarget 为null会咋样呢？
其实ViewGroup也是View的子类，如果没有找到能够处理该事件的子View，或者干脆就没有子View；
那么，它作为一个View，就相当于View的事件转发了~~直接super.dispatchTouchEvent(ev);
final View target = mMotionTarget;
if (target == null) {
// We don't have a target, this means we're handling the
// event as a regular view.
ev.setLocation(xf, yf);
if ((mPrivateFlags & CANCEL_NEXT_UP_EVENT) != 0) {
ev.setAction(MotionEvent.ACTION_CANCEL);
mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;
}
return super.dispatchTouchEvent(ev);
}
我们没有一个能够处理该事件的目标元素，意味着我们需要自己处理~~~就相当于传统的View~
2、那么什么时候子View.dispatchTouchEvent(ev)返回的为true
如果你仔细看了上篇博客，你会发现只要子View支持点击或者长按事件一定返回true~~
源码是这样的：
if (((viewFlags & CLICKABLE) == CLICKABLE ||
(viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)) {
return true ;
总结
1、如果ViewGroup找到了能够处理该事件的View，则直接交给子View处理，自己的onTouchEvent不会被触发；
2、可以通过复写onInterceptTouchEvent(ev)方法，拦截子View的事件（即return true），把事件交给自己处理，则会执行自己对应的onTouchEvent方法
3、子View可以通过调用getParent().requestDisallowInterceptTouchEvent(true); 阻止ViewGroup对其MOVE或者UP事件进行拦截；
实际应用中能解决哪些问题呢？
比如你需要写一个类似slidingmenu的左侧隐藏menu，主Activity上有个Button、ListView或者任何可以响应点击的View，你在当前View上死命的滑动，菜单栏也出不来；因为MOVE事件被子View处理了,你需要这么做：在ViewGroup的dispatchTouchEvent中判断用户是不是想显示菜单，如果是，则在onInterceptTouchEvent(ev)拦截子View的事件；自己进行处理，这样自己的onTouchEvent就可以顺利展现出菜单栏了~~