Question

In my example activity, I have
– a ListView containing
– multiple HorizontalScrollView containing
– a set of TextView

The horizontal scrolling experience is rather bad though.
When I initiate a horizontal scroll (or fling), I must be very careful to make it work.

As soon as the horizontal scroll contains a (small) vertical component, the vertical ListView scrolling takes over and stops the horizontal scrolling completely.

Any suggestion on how to improve this?

Thanks in advance,

Marc

import android.app.Activity;
import android.database.DataSetObserver;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.HorizontalScrollView;
import android.widget.LinearLayout;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.RelativeLayout;
import android.widget.TextView;

public class Test extends Activity 
{
private final static int N = 20;//number of HorizontalScrollView
private final static int M = 20;//number of TextViews inside a single HorizontalScrollView


@Override
protected void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    LinearLayout layout = new LinearLayout(this);
    //create a list of HorizontalScrollViews
    final HorizontalScrollView[] hors = new HorizontalScrollView[N];
    for (int i = 0; i < hors.length; i++)
    {
        hors[i] = new HorizontalScrollView(this, null);
        hors[i].setMinimumHeight(60);
        LinearLayout ll = new LinearLayout(this);
        ll.setOrientation(LinearLayout.HORIZONTAL);
        hors[i].addView(ll);
        for (int j = 0; j < M; j++)
        {
            TextView t = new TextView(Test.this);
            t.setText("HorizontalScrollView: "+i+"; TextView: "+j);
            t.setMinimumHeight(40);
            ll.addView(t);
        }
    }
    //add a ListView
    ListView list = new ListView(this);
    layout.addView(list);
    list.setAdapter(new BaseAdapter()
    {

        @Override
        public View getView(int position, View convertView, ViewGroup parent)
        {
            return hors[position];
        }

        @Override
        public long getItemId(int position)
        {
            return 0;
        }

        @Override
        public Object getItem(int position)
        {
            return hors[position];
        }

        @Override
        public int getCount()
        {
            return N;
        }
    });

    setContentView(layout);

}


}

Answer 1

The problem is that ListView (or rather its parent AbsListView) implements onInterceptTouchEvent and hence ListView can intercept all touch events as soon as it considers it is in a better position to handle them.

This can be avoided by calling requestDisallowInterceptTouchEvent, e.g. by subclassing HorizontalScrollView and in its dispatchTouchEvent:

public boolean dispatchTouchEvent(MotionEvent ev)
{
  boolean ret = super.dispatchTouchEvent(ev);
  if(ret) 
  {
    requestDisallowInterceptTouchEvent(true);
  }
  return ret;
}       

It needs some refinement (like only call requestDisallowInterceptTouchEvent if the horizontal component is larger than the vertical one) since now it hardly ever allows the ListView to take control.