In WPF MenuItem, it it possible to use the opposite value of a bool

Question

In WPF, I have two menu items that are mutually opposite (X ticked, then Y unticked and vice versa).

Is it possible to use single bool property to bind these two?

For example below, I have used !IsX and it is not working!

<MenuItem Header="X or Y">
    <MenuItem IsCheckable="True" Header="Is X?" IsChecked="{Binding Path=IsX, Mode=TwoWay}" />
    <MenuItem IsCheckable="True" Header="Is Y?" IsChecked="{Binding Path=!IsX, Mode=TwoWay}" />
</MenuItem>

Answer 1

You need to write a custom converter for that:

[ValueConversion(typeof(bool), typeof(bool))]
public class InverseBooleanConverter: IValueConverter
{
    #region IValueConverter Members

    public object Convert(object value, Type targetType, object parameter,
        System.Globalization.CultureInfo culture)
    {
        if (targetType != typeof(bool))
            throw new InvalidOperationException("The target must be a boolean");

        return !(bool)value;
    }

    public object ConvertBack(object value, Type targetType, object parameter,
        System.Globalization.CultureInfo culture)
    {
        if (targetType != typeof(bool))
            throw new InvalidOperationException("The target must be a boolean");

        return !(bool)value;
    }

    #endregion
}

And then in your markup:

<MenuItem Header="X or Y">
    <MenuItem IsCheckable="True" Header="Is X?" IsChecked="{Binding Path=IsX, Mode=TwoWay}" />
    <MenuItem IsCheckable="True" Header="Is Y?" IsChecked="{Binding Path=IsX, Mode=TwoWay, Converter={StaticResource InverseBooleanConverter}}" />
</MenuItem>

Also you should create an instance of that in your resource file