ios - Objective C syntax understanding

Question

I am a newbie to objective C. I was looking through a few tutorials online to create like a dropdown using the iOS sdk. So I came across the picker view, and from a few online resources I came to know that I would have to provide a delegate and a datasource for the picker.

And the syntax in the header file for the interface is something like this.

@interface ViewController : UIController <UIPickerViewDataSource, UIPickerViewDelegate>

@end

Now, I understand that UIController is the parent of ViewController, but what does the greater than & less than mean here?

Answer 1

<UIPickerViewDataSource, UIPickerViewDelegate> means that the class conforms to these two protocols. Protocols are akin to interfaces in C# and Java^✝; they describe a list of methods you must implement in your class. Your class, ViewController, must implement all methods that are required by the UIPickerViewDataSource and UIPickerViewDelegate protocols.</sup>

See Working with Protocols, UIPickerViewDataSource Protocol Reference and UIPickerViewDelegate Protocol Reference.

^{✝ With the slight difference that methods in protocols can be marked as optional, whereas methods in interfaces are always required.}

Answer 2

Those are called protocols: formal lists of declarations for which the corresponding methods and/or properties are to be implemented by the class that conforms to these protocols.

More about protocols here.