I'm trying to understand OOP so I can write better OOP code and one thing which keeps coming up is this concept of a delegate (using .NET). I could have an object, which is totally self contained (encapsulated); it knows nothing of the outside world... but then I attach a delegate to it. 

In my head, this is still quite well separated as the delegate only knows what to reference, but this by itself means it has to know about something else outside it's world! That a method exists within another class!

Have I got myself it total muddle here, or is this a grey area, or is this actually down to interpretation (and if so, sorry as that will be off topic I'm sure). My question is, do delegates defy/muddy the OOP pattern?


Question: WPF Validation Control Template overlapping
Answer: I'd say this is because your error message is on the AdornerLayer, which doesn't participate in the same layout as your control. MSDN says "rendering of an adorner is independent from rendering of the UIElement that the adorner is bound to." and that is why the message is just put on top of everything.   

You could put the error text into the original template, hide it based on Validation.HasError and include it in the layout process that way.  

But changing the layout of the control might not be the best way to go if a validation error occurs. You might consider providing additional information in a ToolTip.