How to Get Current First Responder from Window Controller in Cocoa?

I would like to find the first responder view in a window. To do this, I would like to implement a category like this: ``` @implementation NSView (ViewExtensions) - (NSView *)findFirstResponder { if ([self isFirstResponder]) { return self; } for (NSView *subView in [self subviews]) { NSView *firstResponder = [subView findFirstResponder]; if (firstResponder != nil) { return firstResponder; } } return nil; } @end ``` The above code is based on this question/answer on SO: Get the current first responder without using a private API. The problem, perhaps, is that NSResponder doesn't have an isFirstResponder method like UIResponder does. What is the equivalent for NSResponder? If the method above is implemented as above, I of course get the debug message: "'NSView' may not respond to 'isFirstResponder'". How do I make findFirstResponder work in Cocoa? Further information: I would later like to use the above method in my window controller in some way like: ``` NSArray *copiedObjects; if ([[self window]contentView] == MyTableView) { copiedObjects = [tableController selectedObjects]; } if ([[self window]contentView] == MyOutlineView) { copiedObjects = [treeController selectedFolders]; } ```