NSArrayController and Bindings

I’m trying out an exercise to make sure I understand the use of the NSArrayController. Here is what I have done… in just the AppDelegate class:
Created instance variables: NSMutableArray *myArray and NSString *myString… @property & @synthesize for each.

In my NIB, I add an NSArrayController and bind it to the AppDelegate.myArray
I add and “Add” button and connect it to the add: outlet on NSArrayController
I configure the Object Controller for the NSArrayController to be Class - NSString

I add an NSTextField to the NIB and bind it to AppDelegate and myString.

I confirm that the “Add” button adds null NSString objects to myArray.
I confirm that the NSTextField is updating myString.

How do I get myString to be the object added to myArray w/out writing the code? The code part is easy. But, I want to do it with only bindings.