Run your app in Simulator to make sure that the UI elements you added look the way you expect them to. If you click the Hello button, it should highlight, and if you click inside the text field, the keyboard should appear. At the moment, though, the button doesn’t do anything, the label just displays “Label,” and there’s no way to dismiss the keyboard after it appears. To add the functionality you want, you need to make the appropriate connections between the UI elements and the view controller. These connections are described next.

Note: Because you’re running the app in Simulator, and not on a device, you activate controls by clicking them instead of tapping them.

Create an Action for the Button

When the user activates a UI element, the element can send an action message to an object that knows how to perform the corresponding action method (such as “add this contact to the user’s list of contacts”). This interaction is part of the target-action mechanism, which is another Cocoa Touch design pattern.
In this tutorial, when the user taps the Hello button, you want it to send a “change the greeting” message (the action) to the view controller (the target). This message changes the string (that is, the model object) that the view controller manages. Then, the view controller updates the text that’s displayed in the label to reflect the change in the model object’s value.
Using Xcode, you can add an action to a UI element and set up its corresponding action method by Control-dragging from the element on the canvas to the appropriate source file (typically, a view controller’s source file). The storyboard archives the connections that you create in this way. Later, when the app loads the storyboard, the connections are restored.

To add an action for the button

When you Control-dragged from the Hello button to the HelloWorldViewController.h file and configured the resulting action, you accomplished two things:

• You added the appropriate code to the view controller class. Specifically, you added the following action method declaration to HelloWorldViewController.h:
  

  - (IBAction)changeGreeting:(id)sender;

  and caused Xcode to add the following stub implementation to HelloWorldViewController.m:
  

  - (IBAction)changeGreeting:(id)sender {

  }

  Note: IBAction is a special keyword that is used to tell Xcode to treat a method as an action for target-action connections. IBAction is defined to void.
  The sender parameter in the action method refers to the object that is sending the action message (in this tutorial, the sender is the button).
• You created a connection between the button and the view controller.

Next, you create connections between the view controller and the two remaining UI elements (that is, the label and the text field).