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

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.

CodePudding user response：

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.