.NET MAUI RadioButtonGroup.SelectedValue does not work

Question

I can't get RadioButtonGroup.SelectedValue to bind to a viewmodel property. I've read everything that you can google including:

https://learn.microsoft.com/en-us/dotnet/maui/user-interface/controls/radiobutton?view=net-maui-9.0#respond-to-a-property-change

https://github.com/dotnet/maui-samples/blob/main/9.0/UserInterface/Views/RadioButtonDemos/RadioButtonDemos/Views/GroupedRadioButtonsViewModelPage.xaml

and other questions asked here.

I have made a simplified example to eliminate extraneous issues. I don't get it, it should work and it should be simple based on documentation.

View

   ...
<Grid>
       <ScrollView >
           <VerticalStackLayout HorizontalOptions="Center" Padding="20,0,20,0" >
               <Label Text="Select the course:"></Label>
               <VerticalStackLayout RadioButtonGroup.SelectedValue="{Binding SelectedThing}">
                   <RadioButton GroupName="FOO" Content="ONE" Value="1"></RadioButton>
                   <RadioButton GroupName="FOO" Content="TWO" Value="2" ></RadioButton>
                   <RadioButton GroupName="FOO" Content="THREE" Value="3"></RadioButton>
               </VerticalStackLayout>
               <Label Text="{Binding SelectedThing, StringFormat='The selection is: {0} (not working!)'}"></Label>
...

ViewModel

(based on mvvm toolkit ObservableObject)

 [ObservableProperty]
 private object selectedThing;

I'm not sure what else might be relevant.

Answer 1

I had to put GroupName at the same level as SelectedValue like this:

<VerticalStackLayout RadioButtonGroup.GroupName="FOO" RadioButtonGroup.SelectedValue="{Binding SelectedThing}">