Issue with TaskResultConverter when using MVVM toolkit with WinUI3 (AsyncRelayCommand)

[omar-awwad]

I created a new WinUI 3 project to try the MVVM toolkit (AsyncRelayCommand sample) ,

I used the same code as in the documentation but I get this error

I think it is related to TaskResultConverter when used in the binding
<Run Text="{x:Bind MyViewModel.DownloadTextCommand.ExecutionTask, Converter={StaticResource TaskResultConverter}, Mode=OneWay}"/> , when i remove the converter attribute ; no error occurs but get this message when click the button :

I used the following package in the Page XAML
xmlns:converters="using:CommunityToolkit.WinUI.UI.Converters"
while the MVVM sample app code use the
xmlns:converters="using:Microsoft.Toolkit.Uwp.UI.Converters"

when trying to install Microsoft.Toolkit.Uwp.UI I get this error :

Error NU1202 Package Microsoft.Toolkit.Uwp.UI 7.1.2 is not compatible with net6.0-windows10.0.19041 (.NETCoreApp,Version=v6.0) / win10-x86. Package Microsoft.Toolkit.Uwp.UI 7.1.2 supports: uap10.0.17763 (UAP,Version=v10.0.17763)

I get confused with which version to use,

here is my project config

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>WinExe</OutputType>
    <TargetFramework>net6.0-windows10.0.19041.0</TargetFramework>
    <TargetPlatformMinVersion>10.0.17763.0</TargetPlatformMinVersion>
    <RootNamespace>App2</RootNamespace>
    <ApplicationManifest>app.manifest</ApplicationManifest>
    <Platforms>x86;x64;arm64</Platforms>
    <RuntimeIdentifiers>win10-x86;win10-x64;win10-arm64</RuntimeIdentifiers>
    <PublishProfile>win10-$(Platform).pubxml</PublishProfile>
    <UseWinUI>true</UseWinUI>
    <EnablePreviewMsixTooling>true</EnablePreviewMsixTooling>
  </PropertyGroup>

................

 <ItemGroup>
	  <PackageReference Include="CommunityToolkit.Mvvm" Version="7.1.2" />
	  <PackageReference Include="CommunityToolkit.WinUI.UI" Version="7.1.2" />
	  <PackageReference Include="Microsoft.WindowsAppSDK" Version="1.0.0" />
	  <PackageReference Include="Microsoft.Windows.SDK.BuildTools" Version="10.0.22000.194" />
	  <Manifest Include="$(ApplicationManifest)" />
  </ItemGroup>

any help?

[omar-awwad]

I think I get to know the source of this error.
I created my own TaskConverterClass as follow: -

public  class MyTaskResultConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, string language)
        {
            Task task = value as Task;
            if (task != null)
            {
                return task.GetResultOrDefault();
            }
            return null;
            // return DependencyProperty.UnsetValue;
        }

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

this line was the source of the error,
return DependencyProperty.UnsetValue;
I comment it and things worked fine,

any explanation for that? is this an issue or did I miss something

[michael-hawker]

@Sergio0694 @azchohfi could this be a WinUI C#/WinRT issue?

@omar-awwad the Microsoft.Toolkit packages are for UWP projects, so you're correct you should be using the CommunityToolkit.WinUI ones instead. Also, if you use Binding instead of x:Bind do you get the same error?

[azchohfi]

Yes, it looks like a CSWinRT issue. I would report this at https://github.com/microsoft/CsWinRT/issues

[omar-awwad]

when referencing default converter and using Binding instead of x:bind, things worked fine without error
xmlns:convert="using:CommunityToolkit.WinUI.UI.Converters"
<Run Text="{Binding Path=DownloadTextCommand.ExecutionTask, Converter={StaticResource TaskResultConverter}, Mode=OneWay}"/>

[michael-hawker]

@omar-awwad that's good to know that the regular Binding works, probably does indicate a CsWinRT issue with the harder cast of x:Bind that Alex mentioned. Mind posting a copy of your issue on the CsWinRT repo (feel free to link back here). Thanks!