BooleanInvertConverter.cs

using System.Globalization;
using System.Windows;
using System.Windows.Data;
 
namespace Vereinsmeisterschaften.Converters;

[ValueConversion(typeof(bool), typeof(bool))]
public class BooleanInvertConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if(value != null && value is bool boolVal)
        {
            return !boolVal;
        }
        return null;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (value != null && value is bool boolVal)
        {
            return !boolVal;
        }
        return null;
    }
}