WPF ObjectDataProvider Parameters

Question

I have an ObjectDataProvider for getting a list of enum members:

<ObjectDataProvider x:Key="GetEnumContents" MethodName="GetValues" ObjectType="{x:Type System:Enum}">
    <ObjectDataProvider.MethodParameters>
         <x:Type TypeName="Data:Status"/>
    </ObjectDataProvider.MethodParameters>
</ObjectDataProvider>

which I then use with:

<ComboBox SelectedItem="{Binding Status, UpdateSourceTrigger=PropertyChanged}" ItemsSource="{Binding Source={StaticResource GetEnumContents}}" />

In the same window, I'd then like to have a combo box for a different enum. How do I pass the enum type from the ComboBox declaration?

I've seen solutions to similar problems something like:

Path="MethodParameters[0]"

but here I don't want to bind the parameter to anything, I just want to hard-code it in the ComboBox declaration.

Any ideas?

I'm pretty sure that ObjectDataProvider doesn't support that kind functionality. You need a provider per type. The ODP just acts as a thin wrapper around the method call. — Bradley Uffner
I think you may be able to rig up an IValueConverter to get the kind of functionality you want though. Give me a few minutes to try it, and if it works out, I'll post an answer for you. — Bradley Uffner

Bradley Uffner Bradley Uffner · Accepted Answer · 2018-10-29T17:22:22

ObjectDataProvider doesn't support that kind of functionality, but you can "fake" it with the clever ~~abuse~~ usage of a Binding and an IValueConverter.

First, the IValueConverter:

class EnumConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return Enum.GetValues((Type)parameter);
    }

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

Here is how you use it:

<Window
    x:Class="EnumTest.MainWindow"
    [...snip...]
    xmlns:local="clr-namespace:EnumTest"
    Title="MainWindow"
    Width="800"
    Height="450"
    mc:Ignorable="d">
    <Window.Resources>
        <local:EnumConverter x:Key="EnumConverter" />
    </Window.Resources>
    <StackPanel>
        <ComboBox ItemsSource="{Binding Converter={StaticResource EnumConverter}, ConverterParameter={x:Type local:MyEnum1}}" />
        <ComboBox ItemsSource="{Binding Converter={StaticResource EnumConverter}, ConverterParameter={x:Type local:MyEnum2}}" />
    </StackPanel>
</Window>

Some Test Enums:

enum MyEnum1
{
    Red,
    Green,
    Blue,
}

enum MyEnum2
{
    Cat,
    Dog,
    Fish,
    Bird,
}

This produces the following output:

This takes advantage of the fact that you can pass an extra parameter to an IValueConverter, which I use to pass the Type of the enumeration to the converter. The converter just calls Enum.GetNames on that argument, and returns the result. The actual Binding will actually be bound to whatever the DataContext of the ComboBox happens to be. The EnumConverter just happily ignores it and operates on the parameter instead.

UPDATE

It works even better by binding directly to the type, skipping the ConverterParameter entirely, like so:

<ComboBox ItemsSource="{Binding Source={x:Type local:MyEnum1}, Converter={StaticResource EnumConverter}}" />

With adjustments to the converter:

public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
    return Enum.GetValues((Type)value);
}

Same result with less typing, and easier to understand, code.

WPF ObjectDataProvider Parameters

1 Answers