Out of control ListView

Question

I'm having a problem with a ListActivity. I've extended ArrayAdapter and Overridden getView to fill in the data for each row. I throw some data from my Adapter's ArrayList into a TextView.

My problem is, when I scroll, the TextView of each row populates with text that is not in its corresponding data in the ArrayList. What I mean is: say I have a row at the top of my list with a TextView that is populated with emptystring. If I'm at the bottom of my list and see a row with a TextView populated with "bob" and I flick to scroll to the top, the row at the top may now have "bob" in its TextView, but the data at that index of my ArrayList does not contain "bob." It contains emptystring (actually null). If I continue scrolling up and down, other rows will populate (or erase) with data that doesn't correspond to what's in the Adapter's ArrayList.

To cause this to happen, I don't need to scroll the ListView fast. However, it appears the faster I scroll, the more rows get messed up.

Here is my code. I realize I'm using findViewById every time getView gets called, but that's beside the point. I'm calling it against convertView; so it should be grabbing the correct TextView on each row, yes?

@Override
public View getView(int position, View convertView, ViewGroup parent) {

    // get the View for this list item
    View v = convertView;
    if (v == null) {
        LayoutInflater vi = (LayoutInflater)getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        v = vi.inflate(R.layout.layout_mylistlist_item, null);
    }

    // get the next object
    MyListItem myItem = m_items.get(position);

    // set up the list item
    if (myItem != null) {
        TextView txtName = (TextView) v.findViewById(R.id.mylist_name);

        // set text
        if (txtName != null && myItem.getName() != null) {
            txtName.setText(myItem.getName());
        }
    }

   // return the created view
    return v;
}

Answer 1

Exchange this

if (v == null) {
        LayoutInflater vi = (LayoutInflater)getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        v = vi.inflate(R.layout.layout_mylistlist_item, null);
    }

with this

if (v == null) {
        LayoutInflater vi = (LayoutInflater)getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        v = vi.inflate(R.layout.layout_mylistlist_item, parent, false);
    }

You have to pass "false" to the inflate(...) method.

If you have time, take a look at this year's I/O session about Android ListView: http://code.google.com/events/io/2010/sessions/world-of-listview-android.html

It's really worth watching it or at least scroll over the slides. They're also online.

Based on your feedback let me propose a way for binding the data with the ArrayAdapter. Maybe that solves your issue.

public class MyTestArrayAdapter extends ArrayAdapter<MyDataModel>{
   private final int resourceId;

   public MyTestArrayAdapter(Context context, int resourceId, List<MyDataModel> myDataModelList) {
      super(context, resourceId, myDataModelList);
      this.resourceId = resourceId;
   }

   @Override
   public View getView(int position, View convertView, ViewGroup parent) {
      if(convertView == null){
         LayoutInflater inflater = (LayoutInflater)getContext().getSystemService....
         convertView = inflater.inflate(resourceId, parent, false);
      }

      MyDataModel modelObj = getItem(position);

      TextView someDataView = convertView.findViewById(....);
      someDataView.setText(modelObj.getDataText());
      ...

      return convertView;
   }

}

I think you don't need to pass your data as a member of your ArrayAdapter. (I didn't try to compile nor run this, so it may need some adjustment)

Answer 2

I think the problem is your if(myItem != null) check at the bottom.

Try adding an else statement to that block that sets the textview to an emptystring.

Like so:

// set up the list item 
TextView txtName = (TextView) v.findViewById(R.id.mylist_name); 
if (myItem != null) {  
    // set text 
    if (txtName != null && myItem.getName() != null) { 
        txtName.setText(myItem.getName()); 
    } else
    {
        txtName.setText("");
    }
} 
else
{
    txtName.setText("");
}

The convertview will still have the old data in it when it is passed to you. You need to intentionally overwrite it even if your data is invalid, or it will keep its old data.