onInterceptTouchEvent and onTouchEvent

onInterceptTouchEvent是ViewGroup特有的，而onTouchEvent是View的，这两个的调用顺序都知道是先onInterceptTouchEvent后onTouchEvent。我这里要说是的onInterceptTouchEvent的拦截过程，先上code:

public class MyLayout extends LinearLayout {
 private static final String TAG = "OnInterceptTouchEventTest";
 public MyLayout(Context context, AttributeSet attrs) {
  super(context, attrs);
 }

 @Override
 public boolean onInterceptTouchEvent(MotionEvent ev) {
  Log.i(TAG, "MyLayout -- onInterceptTouchEvent --- event.getAction() = " + ev.getAction());
  if (ev.getAction() == ev.ACTION_DOWN) {
   return false;
  }
  return true;
 }

 @Override
 public boolean onTouchEvent(MotionEvent event) {
  Log.i(TAG, "MyLayout --- onTouchEvent --- event.getAction() = " + event.getAction());
  return true;
 }
}

public class MyImageView extends ImageView {
 private static final String TAG = "OnInterceptTouchEventTest";
 public MyImageView(Context context, AttributeSet attrs) {
  super(context, attrs);
 }

 @Override
 public boolean onTouchEvent(MotionEvent event) {
  Log.i(TAG, "MyImageView -- event.getAction() = " + event.getAction());
  return true;
 }

06-03 11:13:47.064: INFO/OnInterceptTouchEventTest(21734): MyLayout -- onInterceptTouchEvent --- event.getAction() = 0

06-03 11:13:47.064: INFO/OnInterceptTouchEventTest(21734): MyImageView -- event.getAction() = 0

06-03 11:13:47.142: INFO/OnInterceptTouchEventTest(21734): MyLayout -- onInterceptTouchEvent --- event.getAction() = 2

06-03 11:13:47.142: INFO/OnInterceptTouchEventTest(21734): MyImageView -- event.getAction() = 3

06-03 11:13:47.175: INFO/OnInterceptTouchEventTest(21734): MyLayout --- onTouchEvent --- event.getAction() = 2

06-03 11:13:47.192: INFO/OnInterceptTouchEventTest(21734): MyLayout --- onTouchEvent --- event.getAction() = 2

06-03 11:13:47.225: INFO/OnInterceptTouchEventTest(21734): MyLayout --- onTouchEvent --- event.getAction() = 2

06-03 11:13:47.392: INFO/OnInterceptTouchEventTest(21734): MyLayout --- onTouchEvent --- event.getAction() = 2

06-03 11:13:47.425: INFO/OnInterceptTouchEventTest(21734): MyLayout --- onTouchEvent --- event.getAction() = 2

06-03 11:13:47.562: INFO/OnInterceptTouchEventTest(21734): MyLayout --- onTouchEvent --- event.getAction() = 2

06-03 11:13:47.712: INFO/OnInterceptTouchEventTest(21734): MyLayout --- onTouchEvent --- event.getAction() = 2

06-03 11:13:47.842: INFO/OnInterceptTouchEventTest(21734): MyLayout --- onTouchEvent --- event.getAction() = 1

可见，当onInterceptTouchEvent返回true时截获事件，MyLayout的onTouchEvent就被执行，而MyImageView得到cancel事件,onInterceptTouchEvent也不在拦截，直至下一次down事件到来。所以当我们要在ViewGroup中得到非down事件时，down时就不能返回true，而且childView也要返回true，这样onInterceptTouchEvent才会认为自己没处理到，继续截获下一个事件。