How to implement "inheritance" in Objective-C? How to maintain delegate object while overrriding super class's methods?

Question

I have 2 classes. Son inherits from Dad. (Note code has been simplified)

@interface Dad : NSObject
@interface Son : Dad

Dad Class

- (void)setupSession
{
    dadSession = [NSURLSession config:config delegate:self delegateQueue:mainQueue];    
    // PROBLEM: self == Son, not Dad
}

Son class

- (void)startDadSession
{
    [super setupSession];
}

then someone somewhere calls...

[son startDadSession];

I want the Dad class to be its own delegate for its session, but when I call [super setupSession] from the Son class, when the execution goes into the Dad class self == Son.

Is there a way to have self not be the instance of the Child class here?

Answer 1

Sadly, inheritance and delegates may sometimes interact in bad ways. Generally I find it hard to write code when a class inherits from another class that is a delegate. But it is necessary from time to time.

One solution I try is to override the delegate methods in the subclass and add a check for the correct instance ofNSURLSession, or whichever is the correct object. If it is the wrong session, pass it on to the super class implementation. E.g.

- (void)URLSession:(NSURLSession *)session didBecomeInvalidWithError:(NSError *)error {
    if (session == self.sonSession) {
        // do stuff
    } else {
        // Unknown session, should be the dadSession so pass it on
        [super URLSession:session didBecomeInvalidWithError:error];
    }
}