Question

I don’t understand when I need to invoke the overriden methods or it is just not required.

For example, for dealloc it is necessary

-(void) dealloc
{
   ...
   [super dealloc];
}

For init also I guess..

-(void) init
{
   [super init];
   ..
}

What about viewWillAppear ? and should I invoke the super method before or later my custom code ?

(void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
}

thanks

Answer 1

The only way to know for sure if and when to call super in an overridden method, is to read the documentation for that method.

For the examples you gave:
init: The documentation states:

Subclass versions of init need to incorporate the initialization code
for the classes they inherit from, through a message to super:
…
Note that the message to super precedes the initialization code added
in the method. This sequencing ensures that initialization proceeds in
the order of inheritance.

dealloc: The documentation states:

Subclasses must implement their own versions of dealloc to allow the
release of any additional memory consumed by the object—such as
dynamically allocated storage for data or object instance variables
owned by the deallocated object. After performing the class-specific
deallocation, the subclass method should incorporate superclass
versions of dealloc through a message to super:

viewWillAppear: The documentation states:

You can override this method to perform custom tasks associated with
presenting the view.
…
If you override this method, you must call
super at some point in your implementation.

Every method is different. If you override viewDidAppear:, you must call super. If you override loadView, you must not. Basically, any time you override a method, you should check the documentation for that method to see if you should call super, and if so, whether you should do it before or after your own implementation.

If the documentation doesn’t say, then it’s up to you. After first scolding the author for his omission, do whatever you think makes sense. I’d generally be inclined not to call super if the documentation doesn’t say either way.