How can I put a ListView into a ScrollView without it collapsing?

Question

I\'ve searched around for solutions to this problem, and the only answer I can find seems to be \"don\'t put a ListView into a ScrollView\". I have yet to see any real expl

Answer 1

ListView is actually already capable of measuring itself to be tall enough to display all items, but it doesn't do this when you simply specify wrap_content (MeasureSpec.UNSPECIFIED). It will do this when given a height with MeasureSpec.AT_MOST. With this knowledge, you can create a very simple subclass to solve this problem which works far better than any of the solutions posted above. You should still use wrap_content with this subclass.

public class ListViewForEmbeddingInScrollView extends ListView {
    public ListViewForEmbeddingInScrollView(Context context) {
        super(context);
    }

    public ListViewForEmbeddingInScrollView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public ListViewForEmbeddingInScrollView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, MeasureSpec.makeMeasureSpec(Integer.MAX_VALUE >> 4, MeasureSpec.AT_MOST));
    }
}

Manipulating the heightMeasureSpec to be AT_MOST with a very large size (Integer.MAX_VALUE >> 4) causes the ListView to measure all of its children up to the given (very large) height and set its height accordingly.

This works better than the other solutions for a few reasons:

1. It measures everything correctly (padding, dividers)
2. It measures the ListView during the measure pass
3. Due to #2, it handles changes in width or number of items correctly without any additional code

On the downside, you could argue that doing this is relying on undocumented behavior in the SDK which could change. On the other hand, you could argue that this is how wrap_content should really work with ListView and that the current wrap_content behavior is just broken.

If you're worried that the behavior could change in the future, you should simply copy the onMeasure function and related functions out of ListView.java and into your own subclass, then make the AT_MOST path through onMeasure run for UNSPECIFIED as well.

By the way, I believe that this is a perfectly valid approach when you are working with small numbers of list items. It may be inefficient when compared to LinearLayout, but when the number of items is small, using LinearLayout is unnecessary optimization and therefore unnecessary complexity.