onInterceptTouchEvent和onTouchEvent调用时序
onInterceptTouchEvent()是ViewGroup的一个方法，目的是在系统向该ViewGroup及其各个childView触发onTouchEvent()之前对相关事件进行一次拦截，Android这么设计的想法也很好理解，由于ViewGroup会包含若干childView,因此需要能够统一监控各种touch事件的机会，因此纯粹的不能包含子view的控件是没有这个方法的，如LinearLayout就有，TextView就没有。
onInterceptTouchEvent()使用也很简单，如果在ViewGroup里覆写了该方法，那么就可以对各种touch事件加以拦截。但是如何拦截，是否所有的touch事件都需要拦截则是比较复杂的，touch事件在onInterceptTouchEvent()和onTouchEvent以及各个childView间的传递机制完全取决于onInterceptTouchEvent()和onTouchEvent()的返回值。并且，针对down事件处理的返回值直接影响到后续move和up事件的接收和传递。
关于返回值的问题，基本规则很清楚，如果return true,那么表示该方法消费了此次事件，如果return false，那么表示该方法并未处理完全，该事件仍然需要以某种方式传递下去继续等待处理。
SDK给出的说明如下：
- You will receive the down event here.
- The down event will be handled either by a child of this view group, or given to your own onTouchEvent() method to handle; this means you should implement onTouchEvent() to return true, so you will continue to see the rest of the gesture (instead of looking for a parent view to handle it). Also, by returning true from onTouchEvent(), you will not receive any following events in onInterceptTouchEvent() and all touch processing must happen in onTouchEvent() like normal.
- For as long as you return false from this function, each following event (up to and including the final up) will be delivered first here and then to the target's onTouchEvent().
- If you return true from here, you will not receive any following events: the target view will receive the same event but with the action ACTION_CANCEL, and all further events will be delivered to your onTouchEvent() method and no longer appear here.
由于onInterceptTouchEvent()的机制比较复杂，上面的说明写的也比较复杂，总结一下，基本的规则是：
- down事件首先会传递到onInterceptTouchEvent()方法
- 如果该ViewGroup的onInterceptTouchEvent()在接收到down事件处理完成之后return false，那么后续的move, up等事件将继续会先传递给该ViewGroup，之后才和down事件一样传递给最终的目标view的onTouchEvent()处理。
- 如果该ViewGroup的onInterceptTouchEvent()在接收到down事件处理完成之后return true，那么后续的move, up等事件将不再传递给onInterceptTouchEvent()，而是和down事件一样传递给该ViewGroup的onTouchEvent()处理，注意，目标view将接收不到任何事件。
- 如果最终需要处理事件的view的onTouchEvent()返回了false，那么该事件将被传递至其上一层次的view的onTouchEvent()处理。
- 如果最终需要处理事件的view 的onTouchEvent()返回了true，那么后续事件将可以继续传递给该view的onTouchEvent()处理。
下面用一个简单的实验说明上述复杂的规则。视图自底向上共3层，其中LayoutView1和LayoutView2就是LinearLayout，MyTextView就是TextView：
对应的xml布局文件如下：
<?xml version="1.0" encoding="utf-8"?>
<com.touchstudy.LayoutView1 xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent" >
<com.touchstudy.LayoutView2
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:gravity="center">
<com.touchstudy.MyTextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/tv"
android:text="AB"
android:textSize="40sp"
android:textStyle="bold"
android:background="#FFFFFF"
android:textColor="#0000FF"/>
</com.touchstudy.LayoutView2>
</com.touchstudy.LayoutView1>
下面看具体情况：
1.onInterceptTouchEvent()处理down事件均返回false，onTouchEvent()处理事件均返回true
------------------------------------------------------------------------------------------------------------------------------
04-11 03:58:42.620: DEBUG/LayoutView1(614): onInterceptTouchEvent action:ACTION_DOWN
04-11 03:58:42.620: DEBUG/LayoutView2(614): onInterceptTouchEvent action:ACTION_DOWN
04-11 03:58:42.620: DEBUG/MyTextView(614): onTouchEvent action:ACTION_DOWN
04-11 03:58:42.800: DEBUG/LayoutView1(614): onInterceptTouchEvent action:ACTION_MOVE
04-11 03:58:42.800: DEBUG/LayoutView2(614): onInterceptTouchEvent action:ACTION_MOVE
04-11 03:58:42.800: DEBUG/MyTextView(614): onTouchEvent action:ACTION_MOVE
…… //省略过多的ACTION_MOVE
04-11 03:58:43.130: DEBUG/LayoutView1(614): onInterceptTouchEvent action:ACTION_UP
04-11 03:58:43.130: DEBUG/LayoutView2(614): onInterceptTouchEvent action:ACTION_UP
04-11 03:58:43.150: DEBUG/MyTextView(614): onTouchEvent action:ACTION_UP
------------------------------------------------------------------------------------------------------------------------------
总结：这是最常见的情况，onInterceptTouchEvent并没有做任何改变事件传递时序的操作，效果上和没有覆写该方法是一样的。可以看到，各种事件的传递本身是自底向上的，次序是：LayoutView1->LayoutView2->MyTextView。注意，在onInterceptTouchEvent均返回false时，LayoutView1和LayoutView2的onTouchEvent并不会收到事件，而是最终传递给了MyTextView。
2.LayoutView1的onInterceptTouchEvent()处理down事件返回true，MyTextView的onTouchEvent()处理事件返回true
------------------------------------------------------------------------------------------------------------------------------
04-11 03:09:27.589: DEBUG/LayoutView1(446): onInterceptTouchEvent action:ACTION_DOWN
04-11 03:09:27.589: DEBUG/LayoutView1(446): onTouchEvent action:ACTION_DOWN
04-11 03:09:27.629: DEBUG/LayoutView1(446): onTouchEvent action:ACTION_MOVE
04-11 03:09:27.689: DEBUG/LayoutView1(446): onTouchEvent action:ACTION_MOVE
…… //省略过多的ACTION_MOVE
04-11 03:09:27.959: DEBUG/LayoutView1(446): onTouchEvent action:ACTION_UP
------------------------------------------------------------------------------------------------------------------------------
总结: 从Log可以看到，由于LayoutView1在拦截第一次down事件时return true，所以后续的事件（包括第一次的down）将由LayoutView1本身处理，事件不再传递下去。
3.LayoutView1，LayoutView2的onInterceptTouchEvent()处理down事件返回false，MyTextView的onTouchEvent()处理事件返回false,LayoutView2的onTouchEvent()处理事件返回true
----------------------------------------------------------------------------------------------------------------------------
04-11 09:50:21.147: DEBUG/LayoutView1(301): onInterceptTouchEvent action:ACTION_DOWN
04-11 09:50:21.147: DEBUG/LayoutView2(301): onInterceptTouchEvent action:ACTION_DOWN
04-11 09:50:21.147: DEBUG/MyTextView(301): onTouchEvent action:ACTION_DOWN
04-11 09:50:21.147: DEBUG/LayoutView2(301): onTouchEvent action:ACTION_DOWN
04-11 09:50:21.176: DEBUG/LayoutView1(301): onInterceptTouchEvent action:ACTION_MOVE
04-11 09:50:21.176: DEBUG/LayoutView2(301): onTouchEvent action:ACTION_MOVE
04-11 09:50:21.206: DEBUG/LayoutView1(301): onInterceptTouchEvent action:ACTION_MOVE
04-11 09:50:21.217: DEBUG/LayoutView2(301): onTouchEvent action:ACTION_MOVE
…… //省略过多的ACTION_MOVE
04-11 09:50:21.486: DEBUG/LayoutView1(301): onInterceptTouchEvent action:ACTION_UP
04-11 09:50:21.486: DEBUG/LayoutView2(301): onTouchEvent action:ACTION_UP
----------------------------------------------------------------------------------------------------------------------------
总结： 可以看到，由于MyTextView在onTouchEvent()中return false，down事件被传递给其父view，即LayoutView2的onTouchEvent()方法处理，由于在LayoutView2的onTouchEvent()中return true，所以down事件传递并没有上传到LayoutView1。注意，后续的move和up事件均被传递给LayoutView2的onTouchEvent()处理，而没有传递给MyTextView。
应大家的要求，我把源代码贴上，其实很简单，就是基础文件，主要是用来观察事件的传递。
主Activity: InterceptTouchStudyActivity.Java：
public class InterceptTouchStudyActivity extends Activity {
static final String TAG = "ITSActivity";
TextView tv;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.layers_touch_pass_test);
}
}LayoutView1.java：
public class LayoutView1 extends LinearLayout {
private final String TAG = "LayoutView1";
public LayoutView1(Context context, AttributeSet attrs) {
super(context, attrs);
Log.d(TAG,TAG);
}
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
int action = ev.getAction();
switch(action){
case MotionEvent.ACTION_DOWN:
Log.d(TAG,"onInterceptTouchEvent action:ACTION_DOWN");
// return true;
break;
case MotionEvent.ACTION_MOVE:
Log.d(TAG,"onInterceptTouchEvent action:ACTION_MOVE");
break;
case MotionEvent.ACTION_UP:
Log.d(TAG,"onInterceptTouchEvent action:ACTION_UP");
break;
case MotionEvent.ACTION_CANCEL:
Log.d(TAG,"onInterceptTouchEvent action:ACTION_CANCEL");
break;
}
return false;
}
@Override
public boolean onTouchEvent(MotionEvent ev) {
int action = ev.getAction();
switch(action){
case MotionEvent.ACTION_DOWN:
Log.d(TAG,"onTouchEvent action:ACTION_DOWN");
break;
case MotionEvent.ACTION_MOVE:
Log.d(TAG,"onTouchEvent action:ACTION_MOVE");
break;
case MotionEvent.ACTION_UP:
Log.d(TAG,"onTouchEvent action:ACTION_UP");
break;
case MotionEvent.ACTION_CANCEL:
Log.d(TAG,"onTouchEvent action:ACTION_CANCEL");
break;
}
return true;
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
// TODO Auto-generated method stub
super.onLayout(changed, l, t, r, b);
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
// TODO Auto-generated method stub
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
}
}LayoutView2.java：
public class LayoutView2 extends LinearLayout {
private final String TAG = "LayoutView2";
public LayoutView2(Context context, AttributeSet attrs) {
super(context, attrs);
Log.d(TAG,TAG);
}
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
int action = ev.getAction();
switch(action){
case MotionEvent.ACTION_DOWN:
Log.d(TAG,"onInterceptTouchEvent action:ACTION_DOWN");
break;
case MotionEvent.ACTION_MOVE:
Log.d(TAG,"onInterceptTouchEvent action:ACTION_MOVE");
break;
case MotionEvent.ACTION_UP:
Log.d(TAG,"onInterceptTouchEvent action:ACTION_UP");
break;
case MotionEvent.ACTION_CANCEL:
Log.d(TAG,"onInterceptTouchEvent action:ACTION_CANCEL");
break;
}
return false;
}
@Override
public boolean onTouchEvent(MotionEvent ev) {
int action = ev.getAction();
switch(action){
case MotionEvent.ACTION_DOWN:
Log.d(TAG,"onTouchEvent action:ACTION_DOWN");
break;
case MotionEvent.ACTION_MOVE:
Log.d(TAG,"onTouchEvent action:ACTION_MOVE");
break;
case MotionEvent.ACTION_UP:
Log.d(TAG,"onTouchEvent action:ACTION_UP");
break;
case MotionEvent.ACTION_CANCEL:
Log.d(TAG,"onTouchEvent action:ACTION_CANCEL");
break;
}
return true;
}
}MyTextView.java:
public class MyTextView extends TextView {
private final String TAG = "MyTextView";
public MyTextView(Context context, AttributeSet attrs) {
super(context, attrs);
Log.d(TAG,TAG);
}
@Override
public boolean onTouchEvent(MotionEvent ev) {
int action = ev.getAction();
switch(action){
case MotionEvent.ACTION_DOWN:
Log.d(TAG,"onTouchEvent action:ACTION_DOWN");
break;
case MotionEvent.ACTION_MOVE:
Log.d(TAG,"onTouchEvent action:ACTION_MOVE");
break;
case MotionEvent.ACTION_UP:
Log.d(TAG,"onTouchEvent action:ACTION_UP");
break;
case MotionEvent.ACTION_CANCEL:
Log.d(TAG,"onTouchEvent action:ACTION_CANCEL");
break;
}
return false;
}
public void onClick(View v) {
Log.d(TAG, "onClick");
}
public boolean onLongClick(View v) {
Log.d(TAG, "onLongClick");
return false;
}
}