Using Listview in a scroll view

Question

In my app i did use scroll inside a Scrollview layout(root layout).when i did that the child scroll stopped scrolling.For this i found a solution code

childlistview.setOnTouchListener(new ListView.OnTouchListener() {


        @Override
        public boolean onTouch(View v, MotionEvent event) {
            // TODO Auto-generated method stub
            int action = event.getAction();
            switch (action) {
            case MotionEvent.ACTION_DOWN:
            v.getParent().requestDisallowInterceptTouchEvent(true);
            break;

            case MotionEvent.ACTION_UP:
            v.getParent().requestDisallowInterceptTouchEvent(false);
            break;
            }

            v.onTouchEvent(event);
            return false;
        }
        });

It solved the problem.But i can't understand this code.Can anyone help?

Answer 1

In your case, Scrollview is parent whereas ListView is its child.

So, in normal case when you try to scroll, the ScrollView will intercept that event and the scroll of ScrollView will occur. It will not reach the ListView within as it is already handlled by the parent ScrollView.

However, when you set a TouchListener to the child ListView and override its the onTouch() as you have done, a different behaviour is observed.

 case MotionEvent.ACTION_DOWN: 

This event happens when the first finger is pressed onto the screen.

  v.getParent().requestDisallowInterceptTouchEvent(true);

This will prevent the parent from intercepting the touch event, so that the child can handle the event appropriately.

  case MotionEvent.ACTION_UP:

This event fires when all fingers are off the screen.

  v.getParent().requestDisallowInterceptTouchEvent(false);

This will allow the parent to intercept the touch events thereafter, for rest of the screen leaving the childview.

Hope it helps you.