The main idea:

I want to pass an Action from a ViewModel to a CustomControl, such that whenever these Actions are invoked from the ViewModel, it automatically invokes a method within the CustomControl.

The detailed idea:

I want to be able to show some messages on command. So I have these Actions on my MainViewModel that are invoked whenever I need them to show.

public class MainViewModel
{
    // assuming these get and set methods are basically normal gets and sets
    public Action ShowErrorMsg
    {
        get => GetValue<Action>();
        set => SetValue(value);
    }

    public Action ShowSuccessMsg
    {
        get => GetValue<Action>();
        set => SetValue(value);
    }

    public void SendMessage()
    {
        // some send message logic here
        // ...

        // invoke the actions based on result
        if (sendSuccess)
        {
            ShowSuccessMsg?.Invoke();
        }
        else ShowErrorMsg?.Invoke();
    }
}

I have a CustomLabel control class that extends from Label, and it sits in the MainView.xaml like this, and I want it to pass in said Actions:

<controls:CustomLabel Text="Error!" TextColor="Red"
                      ShowMessageAction="{Binding ShowErrorMsg}" />

<controls:CustomLabel Text="Success!" TextColor="Green"
                      ShowMessageAction="{Binding ShowSuccessMsg}" />

In the CustomLabel class, a BindableProperty will be assigned with any arbitrary Action and I want it to be invoked whenever the Action in MainViewModel is invoked. From there, an animation is fired, and the text fades out in 8 seconds.

public class CustomLabel : Label
{ 
    public static readonly BindableProperty ShowMessageActionProperty =
       BindableProperty.Create(nameof(ShowMessageAction), 
                               typeof(Action), 
                               typeof(CustomLabel), 
                               propertyChanged: OnShowMessageChanged);

    public Action ShowMessageAction
    {
        get => (Action)GetValue(ShowMessageActionProperty);
        set => SetValue(ShowMessageActionProperty, value);
    }
    
    // this should be fired when there is a new Action binded
    public static void OnShowMessageChanged(BindableObject sender, object oldValue, object newValue)
    {
        var thisLabel = sender as CustomLabel;

        var action = newValue as Action;
       
        // subscribe the animation method to the Action that this class is bound to
        action += thisLabel.ShowMessageAnimation;
    }

    // animation is fired when action is called, fades out in 8 seconds
    private void ShowMessageAnimation()
    {
        this.IsVisible = true;

        Timer timer = new Timer(8000);
        timer.Elapsed += (_, _) =>
        {
            Application.Current.Dispatcher.Dispatch(async () =>
            {
                await this.FadeTo(0, 1000);
                this.IsVisible = false;
                this.Opacity = 1;
            });
        };

        timer.Start();
    }
}

However, unless I explicitly specify the Action from within CustomLabel, the Action from MainViewModel and ShowMessageAction don’t sync as it should (sometimes the propertyChanged isn’t even fired at all). Is there a fundamental gap in my knowledge, or is there a workaround/ a better way to approach this that I am completely missing?

What I have tried:

• I have tried assigning ShowMessageAction with MainViewModel.ShowMessage in the constructor and that works fine, but does not allow me to be flexible on which Action I want to pass in.
• I have tried subscribing within the Set method in ShowMessageAction property, manually subscribing from MainView.xaml.cs, to no avail.