AgentSkillsCN

binding-enum-command-parameters

使用 x:Static 标记扩展将枚举值绑定到 WPF CommandParameter。适用于将枚举类型传递给命令，或避免因字符串型命令参数而引发的错误。

SKILL.md
--- frontmatter
name: binding-enum-command-parameters
description: "Binds enum values to WPF CommandParameter using x:Static markup extension. Use when passing enum types to commands or avoiding string-based command parameter errors."

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

code
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

xml
<!-- 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#)

csharp
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)

xml
<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

  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

Related Pattern

EnumToBoolConverter (for checking selection state)

csharp
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;
    }
}