listview - Seamless nested scrolling (Android)

Question

We've all been advised against nesting views that contain a scrolling mechanism. However, in the latest Android release (5.0), the Phone app caught my attention with what seems to be a ListView inside of a ScrollView.

What really intrigued me was that the scrolling mechanism switched from the ScrollView to the ListView seamlessly.

Notice the content above the tabs is pushed out of view before the actual ListView begins scrolling.

I've tried duplicating this myself, but ended up unsuccessful. Here is the basic approach I was taking...

With a single, continuous touch event (no lifting of the finger) ...

As user scrolls, the ListView slowly covers up the ImageView. Once the ImageView is 100% covered and the ListView takes up the entire screen, the ListView begins to scroll.

I'm currently listening to touch events on the ListView and if the top has been reached, call requestDisallowInterceptTouchEvent on the ListView, i.e.

@Override
public boolean onTouch(View v, MotionEvent event) {
  if (listViewAtTop) {
    v.requestDisallowInterceptTouchEvent(true);
  } else {
    v.requestDisallowInterceptTouchEvent(false);
  }
  return false;
}

The switching scrolling context works, only if you lift your finger and continue scrolling.

Is there a different approach that will achieve the desired effect?

Answer 1

Android 5.0 Lollipop (API 21) added nested scrolling support.

From what I can tell, both ListView (AbsListView) and ScrollView support this now (if running on API 21), but it must be enabled on the scrolling views.

There are two ways, by calling setNestedScrollingEnabled(true) or with the layout attribute android:nestedScrollingEnabled="true" (which is undocumented)

To learn about how it works, or to support this for a custom widget, the key methods are these:

• onStartNestedScroll

• onNestedScrollAccepted

• onNestedPreScroll

• onNestedScroll

• onStopNestedScroll

Unfortunately, there is no guide or training which explains how this works other than the JavaDoc itself which is rather light and there are no examples other than ScrollView.