Is there any way to convert the members of a collection used as an ItemsSource?

Question

In WPF you can use an IValueConverter or IMultiValueConverter to convert a data-bound value from say an int to a Color.

I have a collection

Answer 1

Yes you can. It is acting the same as with the IValueConverter. You simply treat the value parameter for the Convert method as a collection.

Here is an example of Converter for a collection:

public class DataConvert : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        ObservableCollection convertible = null;
        var result = value as ObservableCollection;

        if (result != null)
        {
            convertible = new ObservableCollection();
            foreach (var item in result)
            {
                if (item == "first")
                {
                    convertible.Add(1);
                }
                else if (item == "second")
                {
                    convertible.Add(2);
                }
                else if (item == "third")
                {
                    convertible.Add(3);
                }
            }
        }

        return convertible;
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

In this case is just a proof of concept, but I think it should show the idea very well. The Converter converts from a simple collection of strings like this:

ModelItems = new ObservableCollection();
        ModelItems.Add("third");
        ModelItems.Add("first");
        ModelItems.Add("second");

into a collection of integers corresponding to the string meaning.

And here is the corresponding XAML (loc is the reference of the current assembly where is the converter):

If you want to make a two way binding, you have to implement also the convert back. From the experience of working with MVVM, i suggest to use something like the Factory Pattern to transform from Model in ViewModel and backwards.