Question

I’m using MVVM, in case it makes a difference.

My MainWindowViewModel has two DependencyProperties, TheList, and TheSelectedItem. TheList is a List<Type>, TheSelectedItem is a Type.

The MainWindow has a ComboBox. When the MainWindowViewModel loads it grabs a list of all the classes in the assembly that implement IMyInterface and sets TheList to this.

Each of these classes has a custom attribute applied called DisplayName, which has one parameter, that will be used to show a user-friendly name for the class instead of the name the application knows about for the class.

I’ve also got a ValueConverter for the express purpose of converting these types into the display names.

    public class TypeToDisplayName : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            if (targetType.Name == "IEnumerable")
            {
                List<string> returnList = new List<string>();
                if (value is List<Type>)
                {
                    foreach (Type t in value as List<Type>)
                    {
                        returnList.Add(ReflectionHelper.GetDisplayName(t));
                    }
                }

                return returnList;
            }
            else
            {
                throw new NotSupportedException();
            }
        }

        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            return typeof(BasicTemplate);
        }
    }

So, what I wind up with is a ComboBox with a list of names in it that the user should be able to understand. Awesome! This is just what I want!

Next step: I bind the SelectedItem property of my ComboBox to my TheSelectedItem property in my ViewModel.

Here’s the problem: When I make a selection, I get a little red box around my ComboBox and the TheSelectedItem property on my ViewModel never gets set.

I’m pretty sure it’s because of a type mismatch (the items in the ComboBox appear to be strings now, and TheSelectedItem is of type Type–also, when I change TheSelectedItem to a string instead of a Type, it works). But I don’t know where I need to start coding to convert the (hopefully unique) DisplayName that’s in the ComboBox back to a Type object.

Thanks in advance for any help. I’m pretty stumped on this one.

Answer 1

If I understand your question correctly then you use that Converter on the ItemsSource for the ComboBox? In that case I think you can let the ItemsSource be like it is and instead just Convert each type when they are presented like this.

<ComboBox ...>
    <ComboBox.ItemTemplate>
        <DataTemplate>
            <TextBlock Text="{Binding Path=typeName, Converter={StaticResource TypeToDisplayNameConverter}}"/>
        </DataTemplate>
    </ComboBox.ItemTemplate>
</ComboBox>

And then just convert each type in the Converter.

public class TypeToDisplayNameConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        Type t = (Type)value;
        return ReflectionHelper.GetDisplayName(t);
    }
    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        return value;
    }
}