WPF Command Parameter Enum Type Binding

WPF Command Parameter Enum Type Binding

MVVM Framework Rule: .claude/rules/dotnet/wpf/mvvm-framework.md 설정에 따라 코드 스타일이 결정됩니다. Prism 9 사용 시 → PRISM.md 참조

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.

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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}" />

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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>

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Important Notes

1. Namespace declaration required: Must declare the assembly and namespace where enum is defined in XAML
2. Assembly reference: Specify assembly= when using enum from different project
3. Also applies to Converter: Use x:Static for ConverterParameter as well

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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;
    }
}