IBOutlet and IBAction

Question

What is the purpose of using IBAction and IBOutlet in Objective-C coding for the iPhone, does it make any difference if I don't use them?

Answer 1

You need to use IBOutlet and IBAction if you are using interface builder (hence the IB prefix) for your GUI components. IBOutlet is needed to associate properties in your application with components in IB, and IBAction is used to allow your methods to be associated with actions in IB. As a simple example, suppose you defined a button and label in IB. To dynamically change the value of the label by pushing the button, you would define an action and property in your app similar to:

UILabel IBOutlet *myLabel;
-(IBAction) pushme;

Then in IB you would connect myLabel with the label and connect the pushme method with the button. You need IBAction and IBOutlet for these connections to eist in IB

Answer 2

IBAction and IBOutlets are used to hook up your interface made in Interface Builder with your controller. If you wouldn't use Interface Builder and build your interface completely in code, you could make a program without using them. But in reality most of us use Interface Builder, once you want to get some interactivity going in your interface, you will have to use IBActions and IBoutlets.

Answer 3

IBAction and IBOutlet are macros defined to denote variables and methods that can be referred to in Interface Builder.

IBAction resolves to "void" and IBOutlet resolves to nothing, but they signify to Xcode and Interface builder that these variables and methods can be used in Interface builder to link UI elements to your code.

If you're not going to be used Interface Builder at all, then you don't need them in your code, but if you are going to use it, then you need to specify IBAction for methods that will be used in IB and IBOutlet for objects that will be used in IB.

Answer 4

Interface Builder uses them to determine what members and messages can be 'wired' up to the interface controls you are using in your window/view.

IBOutlet and IBAction are purely there as markers that Interface Builder looks for when it parses your code at design time, they don't have any affect on the code generated by the compiler.