Do I always have to call [super viewDidLoad] in the -viewDidLoad method?

In Apple's scrollView example they don't call that. I always thought that's a must. Why should I call that anyways?

Solution 1:

If you are overriding the method you should still call the method in the super. Even if the super class is not doing anything with it today, Apple might one day change the implementation and your code will mysteriously stop working. If you really don't need to do anything in that method, leave it out of your code entirely, and the super's method will run as usual, without any intervention on your part.

Solution 2:

No, you don't need to call [super viewDidLoad]. Edit: But read below, because I think you definitely should.

Let's be real here: Apple is not going to break thousands of apps, including those based on their published sample code, by deciding an event they're not currently handling suddenly needs to do something that developers may or may not want to stop and it's critical that if you don't need different behavior you not stop the event.

Edit: Having watched how Apple handles compatibility for an extra year, I now recommend learning and using the correct pattern. While I doubt your application binary will ever suddenly stop working, it's clear that the iPhone detects which SDK your binary was built against and modifies some OS behaviour based on this.

Apple might one day require a particular pattern be followed on some future SDK. This would not affect you until you rebuild with the latest Xcode + SDK, but then you'd get these breaks without any source code changes. Learn and follow the pattern to be safe.

Solution 3:

As Markus says, UIViewController doesn't do anything in its viewDidLoad method, so you don't have to call it. However, it's a good habit to get into, in case you change your inheritance structure and suddenly the class that used to inherit from UIViewController now inherits from something that does do something in the viewDidLoad method.

Solution 4:

Lets say you have 2 class, a Parent and a Child. Child inherits from Parent. They have a method called greet which returns a string.

Here is what the parent method looks like:

Code:

-(NSString *)greet {
   return @"Hello";
}

We want the child to learn from his parents. So we use super to say greet how Mommy would greet, but with our own little additions too.

Code: // Inherits from Parent

-(NSString *)greet {
  NSString *parentGreeting = [super greet];
  return [parentGreeting stringByAppendingString:@", Mommy"]
}

So now Parent greets "Hello", and the Child greets "Hello, Mommy". Later on, if we change the parent's greet to return just "Hi", then both classes will be affected and you will have "Hi" and "Hi, Mommy".

super is used to call a method as defined by a superclass. It is used to access methods that have been overriden by subclasses so that the class can wrap its own code around a method that it's parent class implements. It's very handy if you are doing any sort of inheritance at all.

Solution 5:

Apple's documentation for viewDidLoad does NOT state that you should call [super viewDidLoad], so I would go with what Apple's says. Note, however, that for other similar methods like viewDidAppear, you must call [super viewDidAppear].