Question

I have a simple ComboBox that has some simple values. I’m trying to do 2 way binding with an enum property on my model.

<ComboBox d:LayoutOverrides="Height" Grid.Column="1" SelectedItem="{Binding SortType, Converter={StaticResource sortSelect}, Mode=TwoWay}">
      <ListBoxItem Content="Ascending" Tag="Ascending"/>
      <ListBoxItem Content="Descending" Tag="Descending"/>
      <ListBoxItem Content="Absolute Ascending" Tag="AbsoluteAscending"/>
      <ListBoxItem Content="Absolute Descending" Tag="AbsoluteDescending" />
    </ComboBox>

Here is my ValueConverter

public class RdiSortMatchConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        var val = (RdiSort) value;
        switch (val)
        {
            case RdiSort.Ascending:
                return "Ascending";
            case RdiSort.Descending:
                return "Descending";
            case RdiSort.AbsoluteAscending:
                return "Absolute Ascending";
            case RdiSort.AbsoluteDescending:
                return "Absolute Descending";
            default:
                throw new ArgumentOutOfRangeException();
        }
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return (RdiSort) Enum.Parse(typeof (RdiSort), (string) ((ListBoxItem) value).Tag);
    }
}

The ConvertBack method works fine, and updates my model based on the Tag value in the ListBoxItem, but I cant get the initial Enum value to select the correct ListBoxItem

whats the best way about achieving this, or is there a better way of binding t Enums (take into consideration that I need custom descriptions for each Enum value.

Answer 1

You can do it like this. First add a description for each of your Enum values

public enum RdiSort
{ 
    [Description("Ascending Description")] 
    Ascending, 
    [Description("Descending Description")] 
    Descending, 
    [Description("AbsoluteAscending Description")] 
    AbsoluteAscending,
    [Description("AbsoluteDescending Description")] 
    AbsoluteDescending
} 

Then use an ObjectDataProvider for your ComboBox

xmlns:sys="clr-namespace:System;assembly=mscorlib"
xmlns:MyEnumerations="clr-namespace:MyEnumerations" 

<ObjectDataProvider MethodName="GetValues" 
                    ObjectType="{x:Type sys:Enum}" 
                    x:Key="RdiSortValues"> 
    <ObjectDataProvider.MethodParameters> 
        <x:Type TypeName="MyEnumerations:RdiSort" /> 
    </ObjectDataProvider.MethodParameters> 
</ObjectDataProvider> 

Use the RdiSortValues provider in your ComboBox and create a DataTemplate with a TextBlock and a Converter to see the Description instead of the Enum value.

<local:EnumDescriptionConverter x:Key="EnumDescriptionConverter"/>

<ComboBox SelectedItem="{Binding SortType}"
          ItemsSource="{Binding Source={StaticResource RdiSortValues}}">
    <ComboBox.ItemTemplate>
        <DataTemplate>
            <TextBlock Text="{Binding Converter={StaticResource EnumDescriptionConverter}}"/>
        </DataTemplate>
    </ComboBox.ItemTemplate>
</ComboBox>

And finally the converter. There is no need to ConvertBack since the converter is only used in the TextBlock for displaying.

public class EnumDescriptionConverter : IValueConverter
{
    private string GetEnumDescription(Enum enumObj)
    {
        FieldInfo fieldInfo = enumObj.GetType().GetField(enumObj.ToString());
        object[] attribArray = fieldInfo.GetCustomAttributes(false);
        if (attribArray.Length == 0)
        {
            return enumObj.ToString();
        }
        else
        {
            DescriptionAttribute attrib = attribArray[0] as DescriptionAttribute;
            return attrib.Description;
        }
    }

    object IValueConverter.Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (value != null)
        {
            RdiSort myEnum = (RdiSort)value;
            string description = GetEnumDescription(myEnum);
            return description;
        }
        return null;
    }
    object IValueConverter.ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return string.Empty;
    }
}