File Scope? Swift Delegates and Protocols

Question

I'm working on building a new Swift app roughly based off an old Obj-c app. I'm currently working on the delegates

Here is what my obj-c code looked like in the .h file

@interface MyAppViewController : CustomViewController
@property (nonatomic, weak) id<MyAppViewControllerDelegate> delegate;
@end

@protocol MyAppViewControllerDelegate <NSObject>
- (void)myAppViewController:(MyAppViewController *)controller loggedInStudent:    (MYStudent *)student;
- (void)myAppViewControllerWantsSignUp:(MyAppViewController *)controller;
@end

In SWIFT I did:

class MyAppViewController: CustomViewController {

var delegate: MyAppViewControllerDelegate?
protocol MyAppViewControllerDelegate{
func myAppViewController(controller: MyAppViewController, loggedInStudent:     MYStudent)
func myAppViewControllerWantsSignUp(controller: MyAppViewController)

I've done a lot of reading and study on this, so I thought I was doing it basically right (totally new to swift though... so)

I'm getting this error though, "Declaration is only valid in file scope" on the protocol MyAppViewControllerDelegate { I assumed this had something to do with declaring it within the class, so I moved it out, only now my code within the class doesn't recognize the delegate variable I declared..

Any ideas?

Answer 1

Should be this:

protocol MyAppViewControllerDelegate {
    func myAppViewController(controller: MyAppViewController, loggedInStudent:     MYStudent)
    func myAppViewControllerWantsSignUp(controller: MyAppViewController)
}

class MyAppViewController: CustomViewController {

    var delegate: MyAppViewControllerDelegate?
}

Although, if you're following a common pattern where the object that owns MyAppViewController is also its delegate, this may cause memory issues. You can use class typing to allow weak delegation like so:

protocol MyAppViewControllerDelegate : class {
    func myAppViewController(controller: MyAppViewController, loggedInStudent:     MYStudent)
    func myAppViewControllerWantsSignUp(controller: MyAppViewController)
}

class MyAppViewController: CustomViewController {

    weak var delegate: MyAppViewControllerDelegate?
}

This is slightly limiting because it requires you to use a class for your delegate, but it will help avoid retain cycles :)

Answer 2

From what I see in your source code is that you've declared your protocol inside of your class. Just declare the protocol outside of the class declaration and you'll be fine.

Update:

The default access level is set to internal which is defined as

Internal access enables entities to be used within any source file from their defining module, >but not in any source file outside of that module. You typically use internal access when >defining an app’s or a framework’s internal structure.

In contrast to Objective-C or C you don't need a forward declaration if the implementation haven't happened before the usage.

Source: The Swift Programming Language, Access Control