Relax conditions for converters

[FoggyFinder]

MCVE

    public class M2Conv : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            if (value is int v) return v * 2;
            return value;
        }

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

And usage:

public int IntValue { get; } = 42;

<TextBlock Background="Yellow" Text="{Binding IntValue, Converter={StaticResource m2}}}" />

In Avalonia this will not work due to ImplicitConversions restrictions in TryConvertImplicit.

In WPF the same converter works just fine.

Additional thoughts: if I have int property that bound to Text and it works I would expect that if my converter returns int it will work as well.

[grokys]

Hmm, unsure about this one. Avalonia is asking you to convert object value to targetType and you're instead converting the value to a different type.

I need to look into how/why WPF handles this, but my initial thought is that your converter is broken.

[FoggyFinder]

Any decision? :-)

[grokys]

Sorry, I've not had chance to look into it. Any idea where in the WPF codebase it handles IValueConverter returning a type other than the type it was asked for?

[FoggyFinder]

no, sadly

[grokys]

Just to check: what is targetType when your converter is called?

[FoggyFinder]

String

[grokys]

Yeah, so I really think this is a bug in your code. I know that WPF handles it fine, but there's nothing to my knowledge that says that WPF should accept this, I expect it's a case of it working by accident.

[FoggyFinder]

But can it at least gave a warning or something? Because currently it just does nothing so TextBlock is empty.

[FoggyFinder]

Anyway warning is a different Q. Closing the issue since this is not a bug.

[grokys]

Hmm yeah it should be outputting an error to the log. If that's not happening then that is a bug I think.

[FoggyFinder]

There is a error/warning message on master. So I will wait until next release is out and then re-check again.