onInterceptTouchEvent，onTouchEvent仅查看ACTION_DOWN [英] onInterceptTouchEvent, onTouchEvent only see ACTION_DOWN

问题描述

我有一个顶级ViewGroup，我称它为SliderView，我想在其中检测滑动.这通常可以正常工作，但是一个奇怪的失败仍然存在.

I have a top level ViewGroup, which I call SliderView, in which I want to detect swiping. This is mostly working, but one weird failure persists.

SliderView的本质是重写onInterceptTouchEvent，并且在用户实际滑动后，返回"true"以防止其他视图占用MotionEvent.这是一段代码:

The essence of SliderView is to override onInterceptTouchEvent and, once the user is actually swiping, return "true" to prevent other views from seing the MotionEvent. Here is a snip of code:

public class SliderView extends ViewGroup
{
  enum MoveState { MS_NONE, MS_HSCROLL, MS_VSCROLL };
  private MoveState moveState = MoveState.MS_NONE;

  ... other code ...

  public boolean onInterceptTouchEvent(MotionEvent e)
  {
    final int action = e.getAction();
    switch (action & MotionEvent.ACTION_MASK)
    {
      case MotionEvent.ACTION_DOWN:
        moveState = MoveState.MS_NONE;
        break;

      case MotionEvent.ACTION_MOVE:
        if (moveState == MoveState.MS_NONE)
        {
          if (motion is horizontal)
          {
            moveState = MoveState.MS_VSCROLL;
            return true;
          }
          else
            moveState = MoveState.MS_VSCROLL; // let child window handl MotionEvent
        }
        else if (moveState == MoveState.MS_HSCROLL)
          return true; // don't let children see motion event.
    }
    return super.onInterceptTouchEvent (e);
  }

  ... other code ...
}

据我了解，我的SliderView(最外面的视图)应该始终接收onInterceptTouchEvent.在我的一项测试中，顶级子级是A.但是，在以下情况下，这似乎不是.

It is my understanding that my SliderView (which is the outermost view) should always recevie onInterceptTouchEvent. In one of my tests, where the top level child is a However, in the following case, this appears not to be.

当顶级子级是ScrollView时，onInterceptTouchEvent将获得ACTION_MOVE，而我的代码将执行我想要的操作.在另一种情况下，顶级子对象是LinearLayout，则有时会失败:它始终会获得ACTION_DOWN，但仅当用户触摸LinearLayout内的小部件时才会获得ACTION_MOVE；如果触摸空白区域，则只有ACTION_DOWN通过.

When the top level child is a ScrollView, onInterceptTouchEvent gets ACTION_MOVE and my code does what I want. In another case, where the top level child is a LinearLayout, it fails sometimes: it always gets ACTION_DOWN but gets ACTION_MOVE only if the user touches a widget inside the LinearLayout; if touching blank area, only ACTION_DOWN comes through.

我会注意到，它的行为就像是在SliderView外部发生了失败案例触摸一样.但是，如果是这种情况，为什么我会收到ACTION_DOWN事件?

I'll note that it behaves as if the fail-case touches are happening outside the SliderView. However, if that were the case, why would I get the ACTION_DOWN events?

第二条注释:查看ScrollView的源代码，我看到它检查了"inChild"；我还没有弄清楚这是干什么的，它可能有什么用.

Second note: looking at the source code for ScrollView, I see it checking for "inChild"; I have not figured out what that's for and how it might be relevant.

推荐答案

由于user123321的回答这里

Due to the answer of user123321 here

onInterceptTouchEvent仅在父级具有从onTouchEvent返回"true"的子视图时才被调用.一旦孩子返回true，父母现在就有机会拦截该事件

onInterceptTouchEvent only get called if the parent has a child view which returns "true" from onTouchEvent. Once the child returns true, the parent now has a chance to intercept that event

这篇关于onInterceptTouchEvent，onTouchEvent仅查看ACTION_DOWN的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！