WPF DatagridComboBoxColumn displaymemberpath description attribute

Question

DataGrid has AutoGeneratedColumns = true. Some of the properties are enum so the corresponding columns are DatagridComboBoxColumn. Enum definitions have a Description Attribute as follows:

public enum MyEnum
{
    [Description("first")]
    FirstEnum,

    [Description("second")]
    SecondEnum
}

I already have a utility method to display Description attributes in a ComboBox :

public class EnumToItemsSource : MarkupExtension
{
    private readonly Type _type;

    public EnumToItemsSource(Type type)
    {
        _type = type;
    }

    public override object ProvideValue(IServiceProvider serviceProvider)
    {
        return Enum.GetValues(_type).Cast<object>().Select(e => new { Value = e,
            Description = GetEnumDescription((Enum)e) });
    }

    public static string GetEnumDescription(Enum enumObj)
    {
        FieldInfo fieldInfo = enumObj.GetType().GetField(enumObj.ToString());
        object[] attributes = fieldInfo.GetCustomAttributes(false);
        if (attributes.Length == 0)
            return enumObj.ToString();
        else
        {
            DescriptionAttribute attrib = attributes.OfType<DescriptionAttribute>().FirstOrDefault();
            if (attrib != null)
                return attrib.Description;
            else
                return "No description";
        }
    }
}

And I use it in xaml as follows :

<ComboBox ItemsSource="{utils:EnumToItemsSource {x:Type myenums:MyEnum}}"
                              DisplayMemberPath="Description"
                              SelectedValuePath="Value"
                              SelectedValue="{Binding SomeProperty}"/>

Now my question is, how can I apply this to an auto generated column?

EDIT First try

I've try a first solution by doing it in the AutoGeneratingColumn event handler :

private void OnAutoGeneratingColumn(object sender, DataGridAutoGeneratingColumnEventArgs e)
    {
        DataGridComboBoxColumn col = e.Column as DataGridComboBoxColumn;
        if (col != null)
        {
            col.ItemsSource = EnumToIEnumerable.GetIEnumerable(e.PropertyType);
            col.DisplayMemberPath = "Value";
            col.SelectedValuePath = "Key";
            col.SelectedValueBinding = new Binding(e.PropertyName);
        }
    }

For that, I had to write a new helper static method to provide the list for the combobox items source :

public static class EnumToIEnumerable
{
    public static IEnumerable<KeyValuePair<Enum, string>> GetIEnumrable(Type type)
    {
        return Enum.GetValues(type).Cast<Enum>().Select((e) => new KeyValuePair<Enum, string>(e,
            EnumDescriptionConverter.GetEnumDescription((Enum)e)));
    }
}

It's working for displaying the description. But the programm cannot convert SelectedValue to the bound property. It throws silent exceptions and the combobox is red lined.

I try to translate the error message in english :

Conversion of EnumConverter is not possible from System.Collections.Generic.KeyValuePair
System.Windows.Data Error: 7 : ConvertBack cannot convert value '[Surface, m²]' (type 'KeyValuePair`2'). BindingExpression:Path=TypeQuantite; DataItem='MscaGridLineViewModel' (HashCode=39414053); target element is 'TextBlockComboBox' (Name=''); target property is 'SelectedItem' (type 'Object') NotSupportedException:'System.NotSupportedException: Conversion de EnumConverter impossible à partir de System.Collections.Generic.KeyValuePair`2[[System.Enum, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089],[System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]].

I don't understand why it's written target property is 'SelectedItem' because the SelectedValuePath contains an Enum object and the SelectedValueBinding binds it to a Property of Type "MyEnum" which is an enum.

Answer 1

The answer : I only had to add the line col.SelectedItemBinding = null;

private void OnAutoGeneratingColumn(object sender, DataGridAutoGeneratingColumnEventArgs e)
{
    DataGridComboBoxColumn col = e.Column as DataGridComboBoxColumn;
    if (col != null)
    {
        col.ItemsSource = EnumToIEnumerable.GetIEnumerable(e.PropertyType);
        col.DisplayMemberPath = "Value";
        col.SelectedValuePath = "Key";
        col.SelectedValueBinding = new Binding(e.PropertyName);
        col.SelectedItemBinding = null;
    }
}