Hello, I have an NSPopUpButton, an NSMutableArray of custom objects in my app delegate, and an array controller for it. I have a problem where adding an object to the array, either directly with addObject: or using the same on the controller WILL NOT CHANGE THE MENU. The object is added to the array ok, but it doesn't update. Here are my bindings: Controller Content Array -> App Delegate.constantArray conPopUp Content -> controller.arrangedObjects Content values -> controller.arrangedObjects.listString Selected object -> App Delegate.selectedConstant The custom object is MMConstantFactor which declares a string method 'listString'. The app delegate has an NSMutableArray constantArray and MMConstantFactor selectedConstant. Any help is massively appreciated, I'm in a rush!