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Cocoa Programming for OS X: The Big Nerd Ranch Guide by Aaron Hillegass, Adam Preble, Nate Chandler

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Challenge: Add Menu Item Validation

Add menu item validation to disable the Configure Die menu item if no DieView is presently first responder. If you need to, refer back to the section in Chapter 21.

One hint: the is operator returns true if the left operand is of the same type as the right operand.

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