Question

What is / are the differences between declaring these Protocols these ways? Is it just that the ones in the .h file are publicly available?

in .h file:
@interface TestViewController : UIViewController <UITableViewDataSource, UITableViewDelegate>

in .m file:
@interface TestViewController () <UISearchBarDelegate, UISearchDisplayDelegate, UIAlertViewDelegate, MKMapViewDelegate, CLLocationManagerDelegate>

Answer 1

When you add the protocols to the .h file, this tells everyone that includes the header file that the class adheres to the given protocols.

When you add the protocols to the .m file, this is essentially a private indication that the class adheres to the protocols. Only the implementation knows.

You should only use the first form (in the .h file) when outside classes need to know that the class adheres to the protocol. You should use the second form (in the .m file) when only the implementation cares.

In the example you gave, it is highly unlikely that other classes need to know about the class adhering to the table view protocols. Those should be in the .m file. It’s also unlikely any other class needs to know about the search protocols. These are implementation details. These belong in the .m file.

There may be cases where you use both. This is fine.

Here’ my guideline. Put it in the .m file unless you have a specific need to let other classes know about the use of the protocol.