Binding checked menu items to ViewModel commands

Question

I have in XAML 3 menu items defined (using WPF-MDI):

<MenuItem Header="_Generic" Name="Generic" ToolTip="Generic Visual Studio designer theme" 
          Command="{Binding Path=SelectGenericTheme}"/>
<MenuItem Header="_Luna" Name="Luna" ToolTip="Blue Windows XP theme"
          Command="{Binding Path=SelectLunaTheme}"/>
<MenuItem Header="_Aero" Name="Aero" ToolTip="Windows Vista/7 theme" 
          Command="{Binding Path=SelectAeroTheme}"/>

And the definitions of the commands and current selection in the ViewModel:

    public enum ESelectedTheme
    {
        Generic,
        Luna,
        Aero
    }

    ESelectedTheme _selectedTheme;

    ICommand _selectGenericThemeCommand;
    public ICommand SelectGenericThemeCommand
    {
        get { return _selectGenericThemeCommand ?? (_selectGenericThemeCommand = new RelayCommand(param => SelectGenericTheme(), 
            param => true)); }
    }

    void SelectGenericTheme()
    {
        _selectedTheme = ESelectedTheme.Generic;
    }


    ICommand _selectLunaThemeCommand;
    public ICommand SelectLunaThemeCommand
    {
        get
        {
            return _selectLunaThemeCommand ?? (_selectLunaThemeCommand = new RelayCommand(param => SelectLunaTheme(),
                param => true));
        }
    }

    void SelectLunaTheme()
    {
        _selectedTheme = ESelectedTheme.Luna;
    }


    ICommand _selectAeroThemeCommand;
    public ICommand SelectAeroThemeCommand
    {
        get
        {
            return _selectAeroThemeCommand ?? (_selectAeroThemeCommand = new RelayCommand(param => SelectAeroTheme(),
                param => true));
        }
    }

    void SelectAeroTheme()
    {
        _selectedTheme = ESelectedTheme.Aero;
    }

I have 2 questions (hope that is allowed inside one post):

1. I want to bind the IsChecked property in XAML to the value that is selected (_selectedTheme). I think I need to write a converter but I don't know how.
2. I made 3 copies of ICommands (one for each theme) ... what if I would have 20 themes ... is there a way to make this code parameterized?

Thanks in advance.

Answer 1

It will not be necessary to parameterize the command as the binding will do everything but as noted it would be possible using CommandParameter. Here the converter will get the enum parameter.

An example:

<MenuItem Header="_Description" IsCheckable="True"
        IsChecked="{Binding Path=DisplayMode_Current,
                            Converter={StaticResource EnumToBooleanConv},
                            ConverterParameter=Description}" />
<MenuItem Header="_Web-Page" IsCheckable="True"
        IsChecked="{Binding Path=DisplayMode_Current,
                            Converter={StaticResource EnumToBooleanConv},
                            ConverterParameter=WebPage}" />

The converter can look something like this:

public class EnumToBooleanConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        // You could also directly pass an enum value using {x:Static},
        // then there is no need to parse
        string parameterString = parameter as string;
        if (parameterString == null)
            return DependencyProperty.UnsetValue;

        if (Enum.IsDefined(value.GetType(), value) == false)
            return DependencyProperty.UnsetValue;

        object parameterValue = Enum.Parse(value.GetType(), parameterString);

        return parameterValue.Equals(value);
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        string parameterString = parameter as string;
        if (parameterString == null)
            return DependencyProperty.UnsetValue;

        return Enum.Parse(targetType, parameterString);
    }
}

As the XAML is still verbose (and redundant!) you could take it further by binding the ItemsSource of the parent MenuItem to the enum values and then work with the ItemTemplate and ItemContainerStyle.