View的事件传递机制实例演示
本文通过具体的例子，逐一验证了上一篇文章View事件传递机制源码解析中的结论。结合这两篇文章，View的事件传递机制就了解的非常清楚了。
首先定义一个MyLinearLayout和MyButton，重写几个关键方法，代码如下
MyLinearLayout:
public class MyLinearLayout extends LinearLayout implements OnTouchListener,OnClickListener{
public MyLinearLayout(Context context, AttributeSet attrs) {
super(context, attrs);
this.setOnTouchListener(this);
this.setOnClickListener(this);
// TODO Auto-generated constructor stub
}
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
// TODO Auto-generated method stub
switch (ev.getAction()) {
case MotionEvent.ACTION_DOWN:
Log.d("Event", "MyLinearLayout----> dispatchTouchEvent, Action_DOWN" );
break;
case MotionEvent.ACTION_UP:
Log.d("Event", "MyLinearLayout----> dispatchTouchEvent, Action_UP" );
break;
case MotionEvent.ACTION_MOVE:
Log.d("Event", "MyLinearLayout----> dispatchTouchEvent, Action_Move" );
break;
case MotionEvent.ACTION_CANCEL:
Log.d("Event", "MyLinearLayout----> dispatchTouchEvent, Action_Cancel" );
break;
}
boolean result = super.dispatchTouchEvent(ev);
Log.d("Event", "MyLinearLayout---->dispatchTouchEvent: return value is " + result);
return result;
}
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
// TODO Auto-generated method stub
switch (ev.getAction()) {
case MotionEvent.ACTION_DOWN:
Log.d("Event", "MyLinearLayout----> onInterceptTouchEvent, Action_DOWN" );
break;
case MotionEvent.ACTION_UP:
Log.d("Event", "MyLinearLayout----> onInterceptTouchEvent, Action_UP" );
break;
case MotionEvent.ACTION_MOVE:
Log.d("Event", "MyLinearLayout----> onInterceptTouchEvent, Action_Move" );
break;
case MotionEvent.ACTION_CANCEL:
Log.d("Event", "MyLinearLayout----> onInterceptTouchEvent, Action_Cancel" );
break;
}
return false;
}
@Override
public boolean onTouchEvent(MotionEvent event) {
// TODO Auto-generated method stub
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
Log.d("Event", "MyLinearLayout----> onTouchEvent, Action_DOWN" );
break;
case MotionEvent.ACTION_UP:
Log.d("Event", "MyLinearLayout----> onTouchEvent, Action_UP" );
break;
case MotionEvent.ACTION_MOVE:
Log.d("Event", "MyLinearLayout----> onTouchEvent, Action_Move" );
break;
case MotionEvent.ACTION_CANCEL:
Log.d("Event", "MyLinearLayout----> onTouchEvent, Action_Cancel" );
break;
}
boolean result =super.onTouchEvent(event);
Log.d("Event", "MyLinearLayout---->onTouchEvent: return value is " +result );
return result;
}
@Override
public boolean onTouch(View v, MotionEvent event) {
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
Log.d("Event", "MyLinearLayout----> onTouch, Action_DOWN" );
break;
case MotionEvent.ACTION_UP:
Log.d("Event", "MyLinearLayout----> onTouch, Action_UP" );
break;
case MotionEvent.ACTION_MOVE:
Log.d("Event", "MyLinearLayout----> onTouch, Action_Move" );
break;
case MotionEvent.ACTION_CANCEL:
Log.d("Event", "MyLinearLayout----> onTouch, Action_Cancel" );
break;
}
return true;
}
@Override
public void onClick(View v) {
Log.d("Event", "MyLinearLayout----> onClick, " );
}
}
MyButton：
public class MyButton extends Button{
public MyButton(Context context, AttributeSet attrs) {
super(context, attrs);
// TODO Auto-generated constructor stub
}
@Override
public boolean dispatchTouchEvent(MotionEvent event) {
// TODO Auto-generated method stub
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
Log.d("Event", "MyButton-----> dispatchTouchEvent, Action_DOWN" );
break;
case MotionEvent.ACTION_UP:
Log.d("Event", "MyButton-----> dispatchTouchEvent, Action_UP" );
break;
case MotionEvent.ACTION_MOVE:
Log.d("Event", "MyButton-----> dispatchTouchEvent, Action_Move" );
break;
case MotionEvent.ACTION_CANCEL:
Log.d("Event", "MyButton-----> dispatchTouchEvent, Action_Cancel" );
break;
}
boolean result = super.dispatchTouchEvent(event);
//Log.d("Event", "MyButton----->dispatchTouchEvent: return value is " + result);
return result;
}
@Override
public boolean onTouchEvent(MotionEvent event) {
// TODO Auto-generated method stub
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
Log.d("Event", "MyButton-----> onTouchEvent, Action_DOWN" );
break;
case MotionEvent.ACTION_UP:
Log.d("Event", "MyButton-----> onTouchEvent, Action_UP" );
break;
case MotionEvent.ACTION_MOVE:
Log.d("Event", "MyButton-----> onTouchEvent, Action_Move" );
break;
case MotionEvent.ACTION_CANCEL:
Log.d("Event", "MyButton-----> onTouchEvent, Action_Cancel" );
break;
}
boolean result = super.onTouchEvent(event);
Log.d("Event", "MyButton----->onTouchEvent: return value is " +result );
return result;
}
}
代码很明了，就是打印了各种事件和方法名称。唯一特殊的就是对Layout也实现了onTouch和onClick监听。
然后在Activity中实现Button的onTouch和onClick，同时继承Activity的onTouchEvent方法：
public class ViewActivity extends Activity implements OnClickListener,OnTouchListener{
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.customview_main);
Button mEvButton=(Button)findViewById(R.id.event_btn);
mEvButton.setOnClickListener(this);
mEvButton.setOnTouchListener(this);
}
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
switch (v.getId()) {
case R.id.event_btn:
Log.d("Event", "Button----> onClick" );
break;
default:
break;
}
}
@Override
public boolean onTouch(View v, MotionEvent event) {
// TODO Auto-generated method stub
if (v.getId() == R.id.event_btn){
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
Log.d("Event", "Button----> onTouch, Action_DOWN" );
break;
case MotionEvent.ACTION_UP:
Log.d("Event", "Button----> onTouch, Action_UP" );
break;
case MotionEvent.ACTION_MOVE:
Log.d("Event", "Button----> onTouch, Action_Move" );
break;
case MotionEvent.ACTION_CANCEL:
Log.d("Event", "Button----> onTouch, Action_Cancel" );
break;
default:
break;
}
}
return false;
}
@Override
public boolean onTouchEvent(MotionEvent event) {
// TODO Auto-generated method stub
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
Log.d("Event", "Activity----> onTouch, Action_DOWN" );
break;
case MotionEvent.ACTION_UP:
Log.d("Event", "Activity----> onTouch, Action_UP" );
break;
case MotionEvent.ACTION_MOVE:
Log.d("Event", "Activity----> onTouch, Action_Move" );
break;
case MotionEvent.ACTION_CANCEL:
Log.d("Event", "Activity----> onTouch, Action_Cancel" );
break;
default:
break;
}
return super.onTouchEvent(event);
}
好了，先分析一下上边的代码，看起来很长，但是逻辑很简单：
1.MyLinearLayout和MyButton同时实现了Touch和Click监听
2.MyLinearLayout不消耗事件（Intercept方法返回false）
3:MyButton的onTouch监听返回false，onTouchEvent方法返回的是super.onTouchEvent。
运行一下看下打印的log如下：
1: D/Event(2256): MyLinearLayout----> dispatchTouchEvent, Action_DOWN
2: D/Event(2256): MyLinearLayout----> onInterceptTouchEvent, Action_DOWN
3: D/Event(2256): MyButton-----> dispatchTouchEvent, Action_DOWN
4: D/Event(2256): Button----> onTouch, Action_DOWN
5: D/Event(2256): MyButton-----> onTouchEvent, Action_DOWN
6: D/Event(2256): MyButton----->onTouchEvent: return value is true
7: D/Event(2256): MyLinearLayout---->dispatchTouchEvent: return value is true
8: D/Event(2256): MyLinearLayout----> dispatchTouchEvent, Action_UP
9: D/Event(2256): MyLinearLayout----> onInterceptTouchEvent, Action_UP
10: D/Event(2256): MyButton-----> dispatchTouchEvent, Action_UP
11: D/Event(2256): Button----> onTouch, Action_UP
12: D/Event(2256): MyButton-----> onTouchEvent, Action_UP
13: D/Event(2256): MyButton----->onTouchEvent: return value is true
14: D/Event(2256): MyLinearLayout---->dispatchTouchEvent: return value is true
15: D/Event(2256): Button----> onClick
DOWN事件先传递到ViewGroup的dispatchTouchEvent（第一行），下一步，所有的DOWN必然会进入onInterceptTouchEvent（第二行），返回的是false，继续向下分发，到了MyButton的dispatchTouchEvent（第三行），MyButton是一个单一View，进入dispatch以后，首先判断是否设置了onTouchListener，是的话进入onTouch方法（第四行）。此处我们返回的是false，继续向下传递，进入onTouchEvent（第五行），查看View的onTouchEvent方法就知道，因为Button是CLICKABLE的，返回值必定为true（第六行），DOWN事件在此处被消费，传递返回值true给ViewGroup，MyLinearLayout的dispatch返回true，DOWN事件结束（第七行）。
然后UP事件到来，先进入dispatch（第8行）。按上文的ViewGroup分析结论2，DOWN交给了子View处理，后续事件(UP)，会继续进入Intercept（第9行），返回的是false，不拦截事件，继续向下分发，到了MyButton的dispatchTouchEvent（第10行），然后和DOWN事件一样，依次进入onTouch，onTouchEvent，返回true。
最后执行的是onClick方法，上文对View的分析已经知道了，只有UP才会引发Click，所以最后打印的是Click。
现在修改一下button的onTouch方法，返回true，再查看一下Log，会发现Button的onTouchEvent和Click方法都不会执行了，因为onTouch拦截了事件，不会传递到onTouchEvent。
接下来我们试一下，MyLinearLayout拦截事件的情况，把Intercept返回true,打印Log如下
1: MyLinearLayout----> dispatchTouchEvent, Action_DOWN
2: MyLinearLayout----> onInterceptTouchEvent, Action_DOWN
3: MyLinearLayout----> onTouch, Action_DOWN
4: MyLinearLayout----> onTouchEvent, Action_DOWN
5: MyLinearLayout---->onTouchEvent: return value is true
6: MyLinearLayout---->dispatchTouchEvent: return value is true
7: MyLinearLayout----> dispatchTouchEvent, Action_UP
8: MyLinearLayout----> onTouch, Action_UP
9: MyLinearLayout----> onTouchEvent, Action_UP
10�:MyLinearLayout---->onTouchEvent: return value is true
11: :MyLinearLayout---->dispatchTouchEvent: return value is true
12: MyLinearLayout----> onClick,
可以看到，LinearLayout拦截了事件，交给了自己处理，所以后续事件UP不再进入Intercept，而是直接给了自己的onTouch，因为onTouch返回了false，所以还会继续向下交给onTouchEvent和onClick。
其他的情况可以自己试验一下，如果将Button的onTouch和onTouchEvent都设置返回false，那么，即使MyLinearLayout不消费事件(intercept返回false），事件仍然会交给MyLinearLayout来处理.
最后一种情况，所有的View都不拦截事件，手动把返回值全部改成false。运行一下就会发现，事件最终会传递到Activity的onTouchEvent。
