Custom ArrayAdapter setBackground in getView

Question

I'm working on a ListActivity which will display a bunch of numbers (weights). I would like to change the background of a specific row in the ListView. To do this I have created a custom implementation of the ArrayAdapter class and have overridden the getView method. The adapter accepts a list of numbers and sets the background of the row with the number 20 to yellow (for simplicity reasons).

public class WeightListAdapter extends ArrayAdapter<Integer> {

private List<Integer> mWeights;

public WeightListAdapter(Context context, List<Integer> objects) {
    super(context, android.R.layout.simple_list_item_1, objects);

    mWeights = objects;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    View v = super.getView(position, convertView, parent);

    int itemWeight = mWeights.get(position);
    if (itemWeight == 20) {
        v.setBackgroundColor(Color.YELLOW);
    }
    return v;
}

}

The problem is that not only the row with the number 20 gets the yellow background but also the row with the number 0 (the first row that is) and I'm not sure why this is so.

Am I doing something wrong in the getView method (like calling the super method)? My reasoning for the implementation is: All the returned views should be the same (that's why I'm calling the super method) only the view fitting the if criteria should be changed.

Thanks for your help!

Answer 1

Android's view is re-use a component for each row. I got this problem too.

Answer 2

If it's due to reuse, why don't you add another check for if itemWeight not equal to 20? If not equal, then set the background back to normal.

Answer 3

I did a bit of research to find out how this should be done properly. I'm writing this down for the others with the same problem, as I guess this is the proper way how to do it. Please, let me know, if I am mistaken or if this solution has any flaws I'm not seeing.

public class WeightListAdapter extends ArrayAdapter<Integer> {

private static final int TYPE_COUNT = 2;
private static final int TYPE_ITEM_COLORED = 1;
private static final int TYPE_ITEM_NORMAL = 0;

public WeightListAdapter(Context context, List<Integer> objects) {
    super(context, android.R.layout.simple_list_item_1, objects);
}

@Override
public int getViewTypeCount() {
    return TYPE_COUNT;
}

@Override
public int getItemViewType(int position) {

    int item = getItem(position);

    return (item == 30) ? TYPE_ITEM_COLORED : TYPE_ITEM_NORMAL;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    View v = super.getView(position, convertView, parent);
    switch (getItemViewType(position)) {
    case TYPE_ITEM_COLORED:
        v.setBackgroundColor(Color.YELLOW);
        break;
    case TYPE_ITEM_NORMAL:
        break;
    }

    return v;

}

}

Apparently the base class already implements the logic ensuring the correct convertView is passed to the getView method (based on the getViewItemType and getViewTypeCount methods).