Can I control creation of behaviors?

Question

Is it possible in WPF and Caliburn.Micro to control the creation of a System.Windows.Interactivity.Behavior.Behavior that I've bound in my view?

I have a situation where I want to inject a dependency via the Caliburn.Micro Bootstrapper to one of my custom behaviors, but I really don't want resort to some kind of service locator.

My view looks like this:

<TextBox x:Name="Output">
    <i:Interaction.Behaviors>
        <core:ScrollBehavior />
    </i:Interaction.Behaviors>
</TextBox>

and this is what I'm trying to achieve:

public class ScrollBehavior : Behavior<TextBox>
{
    private readonly IMyExteneralDependency _externalDependency;

    public ScrollBehavior(IMyExteneralDependency externalDependency)
    {
        _externalDependency = externalDependency;
    }

    protected override void OnAttached()
    {
        this.AssociatedObject.TextChanged += this.OnTextChanging;
    }

    protected override void OnDetaching()
    {
        this.AssociatedObject.TextChanged -= this.OnTextChanging;
    }

    private void OnTextChanging(object sender, TextChangedEventArgs e)
    {
        this.AssociatedObject.ScrollToEnd();
    }
}

Anyone have an idea of how I can achieve this?

Answer 1

Unfortunately, WPF is the one in charge of the creation of the class in this scenario. As such, there isn't a direct way to use constructor injection or other similar techniques.

As such, a service locator is a common means of handling this type of scenario. Silverlight even went as far as including MEF's CompositionInitializer for this exact type of scenario, but it was never included in WPF. I blogged a port for WPF that could be used in this type of scenario.