Building Cocoa Applications: A Step by Step Guide

Customizing Buttons and Making Connections

In this section we’ll use IB to add more interface specifications to the Calculator.nib file, including customizing buttons further and making several different types of connections between objects. In order to make connections which involve an object of the Controller class, we need a representation of it in IB.

Instantiating (Creating an Instance of) the Controller Class

Creating the Controller class isn’t enough: we also need to create an object that is a member of this class, called an instance. Then we have to arrange for the numeric keypad of buttons in the Calculator window to send action messages to the instance whenever these buttons are clicked.

1. Make sure the Classes tab is displayed in IB’s Nib File window (titled “MainMenu.nib”), then select the Controller class (recall that it’s a subclass of NSObject). If you have trouble finding it, use the Search feature in the window.

2. Choose IB’s Classes → Instantiate Controller menu command.

This will create an icon called “Controller” under the Instances tab in the Calculator’s Nib File window, as shown in Figure 5-17 (IB automatically displays the Instances tab view). This icon represents an instance object of the Controller class — it can be used as the target object of action messages and also to initialize outlets. You can change the name from “Controller” to something else if you like — the name isn’t used for anything except your convenience in IB. Note the little circles with exclamation ...