如何通过ConverterParameter将TimeSpan.FromSeconds传递给转换器？

Question

Given the following :

namespace Foo.Converters {
    public class TimespanConverter : IValueConverter {
        public object Convert( object value, Type targetType, object parameter, CultureInfo culture ) =>
            ( parameter as Func<double, TimeSpan> )?.Invoke( ( double )( value ) );
        public object ConvertBack( object value, Type targetType, object parameter, CultureInfo culture ) =>
            throw new NotImplementedException( );
    }
}

How can I pass TimeSpan.FromSeconds to the ConverterParameter ?

I've tried the following but it did not work -

<Window
    x:Class="Foo.MyWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:c="clr-namespace:Foo.Converters"
    xmlns:lib="clr-namespace:System;assembly=mscorlib"
    xmlns:local="clr-namespace:Foo"
    mc:Ignorable="d" Title="MainWindow" Height="350" Width="525">
    <Window.Resources>
        <c:TimespanConverter x:Key="TSC" />
    </Window.Resources>
    <Viewbox>
        <TextBlock Text="{Binding
            Seconds, Source={x:Static Application.Current},
            Converter={StaticResource TSC},
            ConverterParameter={x:Static lib:TimeSpan.FromSeconds}}" />
    </Viewbox>
</Window>

I get the error in designer - The member "FromSeconds" is not recognized or is not accessible . I've checked the TimeSpan struct and it is contained within the System namespace ( under the mscorlib assembly ), and I've used .FromFOO countless times for conversions in the past ( just not in this fashion ).

I do know that I could just call TimeSpan.FromSeconds directly in the converter, but I was hoping to have something more flexible.

So is what I'm trying to do possible? How can I do this correctly?

Answer 1

SOLUTION

With thanks to a helpful commenter, the error was in the implementation. Evidently, you cannot implicitly pass method or function names as arguments ( at least, not in from XAML ).

To circumvent this, I have changed the converter code to expose the TimeSpan.FromFOO functions as Func<double,TimeSpan> properties so that they can be passed to the ConverterParameter -

namespace Foo.Converters {
    public class TimespanConverter : IValueConverter {
        public static Func<double, TimeSpan> FromMilliseconds => TimeSpan.FromMilliseconds;
        public static Func<double, TimeSpan> FromSeconds => TimeSpan.FromSeconds;
        public static Func<double, TimeSpan> FromMinutes => TimeSpan.FromMinutes;
        public static Func<double, TimeSpan> FromHours => TimeSpan.FromHours;
        public static Func<double, TimeSpan> FromDays => TimeSpan.FromDays;

        public object Convert(
            object value, Type targetType, object parameter, CultureInfo culture ) =>
            ( parameter as Func<double, TimeSpan> )?.Invoke( ( double )( value ) );
        public object ConvertBack(
            object value, Type targetType, object parameter, CultureInfo culture ) =>
            throw new NotImplementedException( );
    }
}

And the window -

<Window
    x:Class="Foo.MyWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:c="clr-namespace:Foo.Converters"
    xmlns:lib="clr-namespace:System;assembly=mscorlib"
    xmlns:local="clr-namespace:Foo"
    mc:Ignorable="d" Title="MainWindow" Height="350" Width="525">
    <Window.Resources>
        <c:TimespanConverter x:Key="TSC" />
    </Window.Resources>
    <Viewbox>
        <TextBlock Text="{Binding
            Seconds, Source={x:Static Application.Current},
            Converter={StaticResource TSC},
            ConverterParameter={x:Static c:TimespanConverter.FromSeconds}}" />
    </Viewbox>
</Window>

The design-time error has gone away, but the text still doesn't show. I'm less worried about the text actually showing and the best method for implementing this, and this seems to be the best option for now. Additionally, it can be extended to any instance where one may wish to pass a Func as a ConverterParameter.