WPF Command Parameter Enum Type Binding

Problem Scenario

When binding enum values to CommandParameter in WPF, passing as string causes type mismatch error.

Error Message

System.ArgumentException: 'Parameter "parameter" (object) cannot be of type System.String, as the command type requires an argument of type MyNamespace.MyEnum.'

Cause

When specifying CommandParameter="Pan" as a string in XAML, WPF passes it as System.String type. However, if the Command expects a specific enum type, automatic type conversion does not occur.

Solution

Use x:Static to Directly Reference Enum Value

<!-- Namespace declaration --> xmlns:viewmodels="clr-namespace:MyApp.ViewModels;assembly=MyApp.ViewModels"

<!-- Wrong method (passed as String) --> <Button Command="{Binding SelectToolCommand}" CommandParameter="Pan" />

<!-- Correct method (passed as Enum type) --> <Button Command="{Binding SelectToolCommand}" CommandParameter="{x:Static viewmodels:ViewerTool.Pan}" />

Complete Example

ViewModel (C#)

public enum ViewerTool { None, Pan, Zoom, WindowLevel }

public partial class ViewerViewModel : ObservableObject { [ObservableProperty] private ViewerTool _currentTool = ViewerTool.Pan;

[RelayCommand]
private void SelectTool(ViewerTool tool)
{
    CurrentTool = tool;
}

}

View (XAML)

<UserControl xmlns:viewmodels="clr-namespace:MyApp.ViewModels;assembly=MyApp.ViewModels">

<StackPanel Orientation="Horizontal">
    <!-- Select Pan tool -->
    <ToggleButton Content="Pan"
                  Command="{Binding SelectToolCommand}"
                  CommandParameter="{x:Static viewmodels:ViewerTool.Pan}"
                  IsChecked="{Binding CurrentTool,
                             Converter={StaticResource EnumToBoolConverter},
                             ConverterParameter={x:Static viewmodels:ViewerTool.Pan}}" />

    <!-- Select Zoom tool -->
    <ToggleButton Content="Zoom"
                  Command="{Binding SelectToolCommand}"
                  CommandParameter="{x:Static viewmodels:ViewerTool.Zoom}"
                  IsChecked="{Binding CurrentTool,
                             Converter={StaticResource EnumToBoolConverter},
                             ConverterParameter={x:Static viewmodels:ViewerTool.Zoom}}" />

    <!-- Select Window/Level tool -->
    <ToggleButton Content="W/L"
                  Command="{Binding SelectToolCommand}"
                  CommandParameter="{x:Static viewmodels:ViewerTool.WindowLevel}"
                  IsChecked="{Binding CurrentTool,
                             Converter={StaticResource EnumToBoolConverter},
                             ConverterParameter={x:Static viewmodels:ViewerTool.WindowLevel}}" />
</StackPanel>

</UserControl>

Important Notes

• Namespace declaration required: Must declare the assembly and namespace where enum is defined in XAML

• Assembly reference: Specify assembly= when using enum from different project

• Also applies to Converter: Use x:Static for ConverterParameter as well

Related Pattern

EnumToBoolConverter (for checking selection state)

public class EnumToBoolConverter : IValueConverter { public object Convert(object value, Type targetType, object parameter, CultureInfo culture) { return value?.Equals(parameter) ?? false; }

public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
    return (bool)value ? parameter : Binding.DoNothing;
}

}