Why does FrameworkElement's FindResource() Method Accept an Object and not a String?

Question

I understand that calling FindResource() on a FrameworkElement (e.g. a Window) can be used to find a resource in the FrameworkElement's ResourceDictionary.

For example, I've used it many times to access a Style through code to add a new Setter to the Style dynamically. I always pass the x:Key value of the Style as a string into the FindResource() method. Like... Style style = w.FindResource("GridDescriptionColumn") as Style;

My question is, I noticed that FindResource() accepts an argument of type object and not an argument of type string. I can't for the life of my think of a reason I would call FindResource() with an argument that is not a string. It makes me think that I may unaware of other ways to use FindResource().

Does anyone know why FindResource() accepts a parameter type of object and not string? If so, what would be an example of calling FindResource() with a parameter type other than a string?

Thanks.

Answer 1

A resource can have any object as a key. Adding a resource with an object key in code behind is easy and can be useful. In XAML, most of the time you're using a string as the x:Key. However there's a common case where the key is not a string and you might even have used without realizing it:

When a Style has no x:Key, it's applied to every instance of its TargetType. But there's an implicit key added by the compiler: the type of the TargetType itself.

In short, writing <Style TargetType="{x:Type Button}" /> in a resources section is exactly the same as writing <Style TargetType="{x:Type Button}" x:Key="{x:Type Button}" />. To get this resource back from code, you have to use FindResource(typeof(Button)), passing a Type and not a string.