WPF - using an ObjectDataProvider

by Gregor Uhlenheuer on February 6, 2012

The ObjectDataProvider is a pretty neat construct in WPF to build custom data providers for existing types. I find those especially useful when working with enumerations. If you want to list all possible values of an enumeration in a ComboBox, this are the steps you have to take.

First you have to create a static instance of the ObjectDataProvider in some resource dictionary. In the resources of the current window this could look like the following:

<Window.Resources>
    <ObjectDataProvider
        MethodName="GetValues"
        ObjectType="{x:Type sys:Enum}"
        x:Key="myEnumTypeProvider">
        <ObjectDataProvider.MethodParameters>
            <x:Type TypeName="local:MyEnumType"/>
        </ObjectDataProvider.MethodParameters>
    </ObjectDataProvider>
</Window.Resources>

The above lines are roughly equivalent to the invokation of GetValues in your code-behind:

// the enumeration type
public enum MyEnumType
{
    First,
    Second,
    Third
}

// usage of Enum.GetValues to manually set the container's items
internal static void SetComboBoxValues(ComboBox container)
{
    if (container == null)
        throw new ArgumentNullException("container");

    var enumValues = Enum.GetValues(typeof(MyEnumType));
    container.ItemsSource = enumValues;
    container.SelectedIndex = 0;
}

The next step is to add a static binding for the ItemsSource of your container to the new data provider:

<ComboBox
    Name="myTypeSelector"
    ItemsSource="{Binding Source={StaticResource myEnumTypeProvider}}"/>

Notice that you may have to add the necessary namespace declarations (for System in mscorlib and your project’s own namespace) in your XAML’s header like:

xmlns:local=“clr-namespace:MyProject”

Discriminated unions in F#

Using a discriminated union in F# sadly does not work the same way. In order to obtain the types of a union type you have to use reflection and bind the values manually to the container’s ItemsSource.

open System.Windows.Controls
open Microsoft.FSharp.Reflection

type MyUnionType =
    | First
    | Second
    | Third

let getUnionNames =
    FSharpType.GetUnionCases typeof<MyUnionType>
    |> Array.map (fun t -> t.Name)

let setComboBoxValues (cb : ComboBox) =
    cb.ItemsSource <- getUnionNames
    cb.SelectedIndex <- 0

In case you really want to use a real enumeration in F# you have to define the discriminated union like this instead:

let MyRealEnumType =
    | First = 0
    | Second = 1
    | Third = 2

This post is tagged with programming, .net and wpf