better-genshin-impact/Build/MicaSetup/Design/Converters/AddConverter.cs

using System;
using System.Globalization;
using System.Windows.Data;

namespace MicaSetup.Design.Converters;

[ValueConversion(typeof(double), typeof(double))]
public class AddConverter : SingletonConverterBase<AddConverter>
{
    protected override object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (double.TryParse(value?.ToString(), NumberStyles.Any, culture, out var basis)
            && double.TryParse(parameter?.ToString(), NumberStyles.Any, culture, out var subtract))
        {
            return basis + subtract;
        }

        return UnsetValue;
    }
}