implementing protocol methods in objective-c

Question

If I have an protocol (say UIPickerViewDataSource) and I implement its required methods, do I need to declare those methods in the header file of my class?

At the moment I'm not doing so and I get a warning of incomplete implementation (although everything works fine). If I do add the required methods in the then I don't get such warning:

- (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView;
- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component;

Is this the correct behaviour? Is it really necessary to add the declaration for required protocol methods in the header file of my class?

Answer 1

No, you don't. Declaring that the class implements that protocol and implementing the methods is enough. You could still declare them in the header for documentation purposes, though.

Answer 2

The correct way is to declare that your class implements the protocol. If for instance your class is called LordSandwichViewController, then your class interface must look like this:

@interface LordSandwichViewController : UIViewController <UIPickerViewDataSource> {
{
}

So you don't declare the protocol methods in your class interface, only the protocol.

Answer 3

Incomplete implementation warnings tell you that you are not implementing all the required methods you are either:

1. Defining in your header.
2. Declaring a method required by a protocol you're conforming to.

Look at what methods it's expecting, and implement those.