Behavior bindable property with DynamicResource not supported?

[mattleibow]

Discussed in #13691

^{Originally posted by Cybrosys March 4, 2023}
Hi,

I raised this Q&A and also a bug in the MCT repo:
CommunityToolkit/Maui#1054

It is a question related to doing a DynamicResource binding against a bindable property on the StatusBarBehaior, if it is supported or a bug. If it is a bug I think it belongs here in the main MAUI repo.

Here is a link to the bug in the MCT Repo:
CommunityToolkit/Maui#1056

So, is this a bug in the MAUI repo or a limitation? For me as a developer and consumer, since the XAML does not show any error I would expect and assume that I would be able to use a DynamicResource binding for the StatusBarBehavior's StatusBarColor bindable property.

I also expressed in one of my comments that if I wanted to start investigating this, where would I start? I do not know who would own the DynamicResource binding. When doing a normal Bind I would expect it to be owned by the UI element itself, targeting a defined BindingContext. However, DynamicResource bindings seem a bit more "magical" in that they work without a BindingContext being defined/assigned.

There are several issues currently related to DynamicResource bindings not working in .NET 7 but in .NET 6. So I do not know if this problem is related to Behavors specifically or a core issue with DynamicResource.

Update

I got information here CommunityToolkit/Maui#1056 that it can't use DynamicResource because it does not inherit from VisualElement or implement IResourcesProvider.

I would argue that you should be able to use DynamicResource even when not inheriting from VisualElement. The reason being that you can put any type of value into a ResourceDictionary, so in essence it is just a normal binding where the source is the parent or app's ResourceDictionary.

[github-actions]

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[mattleibow]

@mikeparker104 do you have a repro?

[mattleibow]

This may be a workaround:

public static class IconTintColor
{
    public static readonly BindableProperty TintColorProperty =
        BindableProperty.CreateAttached("TintColor", typeof(Color), typeof(IconTintColor), default,
            propertyChanged: OnTintColorChanged);

    private static void OnTintColorChanged(BindableObject bindable, object oldValue, object newValue)
    {
        if (bindable is not View view)
            return;
        
        if (view.Behaviors.OfType<IconTintColorBehavior>().FirstOrDefault() is { } existing)
        {
            existing.TintColor = (Color)newValue;
        }
        else
        {
            var behavior = new IconTintColorBehavior
            {
                TintColor = (Color)newValue
            };
            view.Behaviors.Add(behavior);
        }

    }

    public static Thickness GetTintColor(BindableObject view)
    {
        return (Thickness)view.GetValue(TintColorProperty);
    }

    public static void SetTintColor (BindableObject view, bool value)
    {
        view.SetValue(TintColorProperty, value);
    }
}

Used like:

<Image
    Source="dotnet_bot.png"
    HeightRequest="185"
    Aspect="AspectFit"
    SemanticProperties.Description="dot net bot in a race car number eight"
    local:IconTintColor.TintColor="{DynamicResource TargetColor}">
    <!-- <Image.Behaviors>
        <toolkit:IconTintColorBehavior TintColor="{DynamicResource TargetColor}" />
    </Image.Behaviors> -->
</Image>

[mikeparker104]

@mikeparker104 do you have a repro?

@mattleibow adding repro: https://github.com/mikeparker104/repro_23578

[StephaneDelcroix]

Behaviors are meant to be shared, stateless, and should never have inherited from BO, and not allowing the definition of any BP. We could make this work, but really I think we shouldn't

[ME-MarvinE]

public static class IconTintColor
{
public static readonly BindableProperty TintColorProperty =
BindableProperty.CreateAttached("TintColor", typeof(Color), typeof(IconTintColor), default,
propertyChanged: OnTintColorChanged);

private static void OnTintColorChanged(BindableObject bindable, object oldValue, object newValue)
{
    if (bindable is not View view)
        return;
    
    if (view.Behaviors.OfType<IconTintColorBehavior>().FirstOrDefault() is { } existing)
    {
        existing.TintColor = (Color)newValue;
    }
    else
    {
        var behavior = new IconTintColorBehavior
        {
            TintColor = (Color)newValue
        };
        view.Behaviors.Add(behavior);
    }

}

public static Thickness GetTintColor(BindableObject view)
{
    return (Thickness)view.GetValue(TintColorProperty);
}

public static void SetTintColor (BindableObject view, bool value)
{
    view.SetValue(TintColorProperty, value);
}

}

This works great! Though I had to ammend some mismatching parameter/property types which were preventing the use of hardcoded values.

(GetTintColor was returning a Thickness instead of Color and SetTintColor's value parameter was of type bool instead of Color:

public static class IconTintColor
{
    public static readonly BindableProperty TintColorProperty =
        BindableProperty.CreateAttached("TintColor", typeof(Color), typeof(IconTintColor), default,
            propertyChanged: OnTintColorChanged);

    private static void OnTintColorChanged(BindableObject bindable, object oldValue, object newValue)
    {
        if (bindable is not View view)
            return;
        
        if (view.Behaviors.OfType<IconTintColorBehavior>().FirstOrDefault() is { } existing)
        {
            existing.TintColor = (Color)newValue;
        }
        else
        {
            var behavior = new IconTintColorBehavior
            {
                TintColor = (Color)newValue
            };
            view.Behaviors.Add(behavior);
        }

    }

    public static Color GetTintColor(BindableObject view)
    {
        return (Color )view.GetValue(TintColorProperty);
    }

    public static void SetTintColor (BindableObject view, Color value)
    {
        view.SetValue(TintColorProperty, value);
    }
}