Why are outlets created in the header file instead of the implementation file?

you can create properties (including outlets) and methods in implementation files if you would like by using a class extension inside the implementation. However other classes would be unable to see these properties and methods. Its similar to public/private in other languages (though not exactly) with the interface in the header being "public", while the interface in the implementation is "private" (remember this is not 100% true, someone can still call the methods/access the properties if they know the method signature and ignore compiler warnings. there is not really a true concept of "private" in objective c. )

Some people believe its best not to expose properties to outside classes unless necessary. In my experience most people declare them in the header, but its perfectly fine to put them in the implementation if you want to keep them "hidden"

an example of a class extension inside an implementation file is below:

// start of the class extension
@interface ClassName()

- (void) someMethod;
@property (nonatomic, strong) NSArray *someArray;

@end
// end of the class extension

@implementation ClassName
....

Hi Thomas,

Essentially we declare all our class properties, methods, @IBOutlet's, @IBAction's etc. within our interface as that is the facade as it's known for the class, what happens is the implementation references the interface giving it access to the declarations.

Unlike Swift where you assign all your properties and such in the same single file, you need to be explicit in Objective-C because it's an older programming language.

Hope that helps.