Resolve resources in binding conversion

[ProphetLamb]

Good day all,
my desired behavior is that changing the selection in the view model also changes the foreground color of the TabBarItem.

My attempt is pretty straight forward, yet I am unable to resolve the theme resource Theme.Brushes.Primary.Default to a Brush in the convert.
What library function allows this?

I attempted to work around this using different Styles to no avail. Using a style prevents me from inheriting from Theme.Styles.Buttons.Outline. Here i have the same issue again: To have my style BasedOn the button style I need the Style not the resource key for the style, which requires the TODO_THEME_BRUSH_FROM_KEY function.

Thanks in advance for any advice.

More generally, I am attempting to setup a TabBar for page navigation.

new TabBar().DataContext(new BindableNavigatorModel(), (bar, vm) =>

[...]

new TabBarItem
	.Resources(r => r.Add(icon))
	.Children(
	  new PathIcon()
	    .Data(icon)
	    .Foreground(
	      () => model.SelectedPage,
	      selectedPage => TODO_THEME_BRUSH_FROM_KEY(
	        selectedPage == typeof(MyPage) ? Theme.Brushes.Primary.Default : Theme.Brushes.Primary.Disabled
	      )
	    )
	);

public partial record NavigatorModel
{
    public NavigatorModel()
    {
        App = (App)Application.Current;
        ArgumentNullException.ThrowIfNull(App.Frame?.CurrentSourcePageType);
        SelectedPage = State.Value(this, () => App.Frame.CurrentSourcePageType);
        App.Frame.Navigated += (_, _) => SelectedPage.Update(_ => App.Frame.CurrentSourcePageType, default);
    }

    public App App { get; }

    public IState<Type> SelectedPage { get; }
}

[morning4coffe-dev]

Hey @ProphetLamb,

you should be able to use TryGetValue and apply the value to the Foreground directly. I tested this with a little bit different sample, so you will need to adjust it for your case. But for the general idea, you can do something like this:

.Background(x => x.Binding(() => vm.IsToggleOn).Convert(ConvertIsOnToBrush))

    private Brush ConvertIsOnToBrush(bool isOn) 
    {
        return isOn ? GetBrush("PrimaryBrush") : GetBrush("TertiaryBrush");
    }

    private Brush GetBrush(string key)
    {
        if (Application.Current.Resources.TryGetValue(key, out var brush))
        {
            return brush as SolidColorBrush;
        }

        throw new KeyNotFoundException($"The resource '{key}' was not found.");
    }