Is it possible to create a Xamarin Converter dynamically and in one line?

Question

Xamarin Converters normally have to be static (not changed after start) and classes which makes them quite an overkill for what they do in the most cases. Therefore I thought it would be easier to define them in a one-liner at runtime.

Answer 1

Yes it is possible with an wrapper class and if you create your objects before calling InitializeComponent.

Here is an example wrapper class:

    public class XamarinFormsConverter<TIn, TOut> : IValueConverter {
        private readonly Func<TIn, TOut> _func;

        public XamarinFormsConverter(Func<TIn, TOut> func) => _func = func;

        public object Convert(object value, Type targetType, object _, CultureInfo __) {
            if (targetType != typeof (TOut)) {
                throw new Exception("Converter used with wrong targetType");
            }

            if (value is TIn val) {
                return _func(val);
            }
            throw new Exception("Converter used with wrong inputType");
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) => throw new NotImplementedException();
    }

and an example on how to use it:

        public ResourceDictionary Converters { get; } = new ResourceDictionary {
            ["IsLoggedInToColor"] = new XamarinFormsConverter<bool, Color>(input => input ? Color.FromRgb(132, 255, 255) : Color.FromRgb(64, 196, 255)),
            ["IsLoggedInToView"] = new XamarinFormsConverter<bool, object>(input => input ? Views.User.ToString() : Views.Login.ToString()),
            ["BoolInvert"] = new XamarinFormsConverter<bool, bool>(input => !input),
            ["FromPercent"] = new XamarinFormsConverter<int, double>(input => (double)input / 100)
        };

its important to add the Converters befor initalizing:

        public MainPage() {
            ViewModel = new ViewModel();
            Resources.Add(ViewModel.Converters);
            InitializeComponent();
            BindingContext = ViewModel;
        }

Technicallly it would also be possible to change the behaviors of the converters after the initialization, but the names and objects must be created before.

I hope some people can use this to make their code simpler and more readable.