CODEWITHSUNDEEP
objective-cxcodeoop
OutOnAWeekend
OutOnAWeekend

Reputation: 1453

Understanding what exactly 'self' means

I am having a hard time understanding how a particular code works so I went ahead and added the line

NSLog(@"%@ - %@", [self class], NSStringFromSelector(_cmd));

at the start of every method in the hope that I will be able to see the exact sequence in which the various methods are invoked along with their class names.

However, at times [self class] is returning the name of a class in which the method is not actually present. For example, it shows the following in debug console - PhotographersTableViewController - shouldAutorotateToInterfaceOrientation:, whereas, the method shouldAutorotateToInterfaceOrientation is actually present in CoreDataTableViewController.

How can this happen?

P.S. Also, is there a way in Xcode to add a line in all the methods of a file?

Upvotes: 0

Views: 119

Answers (3)

CRD
CRD

Reputation: 53000

This is due to inheritance, which is fundamental to the way in which Obj-C, and most object-oriented programming languages, work. Glossing over details, this is how it works:

In all probability you have a declaration in your code like:

@interface PhotographersTableViewController : CoreDataTableViewController { ... }

This declares PhotographersTableViewController as an extension of CoreDataTableViewController - PhotographersTableViewController is said to inherit the methods of CoreDataTableViewController.

When you a method call:

PhotographersTableViewController *myPhotoView;
...
[myPhotoView shouldAutorotateToInterfaceOrientation];

Then Obj-C first looks for the method shouldAutorotateToInterfaceOrientation in class PhotographersTableViewController, which fails, and then in class CoreDataTableViewController, which succeeds - so it invokes the method defined in CoreDataTableViewController passing it the current object, i.e. the one referenced by the variable myPhotoView, as the value of the self argument (self is just an argument to the method supplied automatically by Obj-C).

This process is fundamental to inheritance and Obj-C.

Therefore when you print out the value of self you see the original object type.

The above glosses over a lot of detail, much of it very important: no mention of instance variables, hiding, scope, etc., etc. If you're learning Obj-C and object-oriented programming together you need to find a good book and read up on the details.

Upvotes: 4

Shubhank
Shubhank

Reputation: 21805

Self is an instance that is accessing the current method.. And for the other ques.. I don't think there is such an option to put certain line in every method... You can try code snippets though

Upvotes: 0

bandejapaisa
bandejapaisa

Reputation: 26952

If PhotographersTableViewController extends CoreDataTableViewController, then self is PhotographersTableViewController, even though the method exists in CoreDataTableViewController.

Upvotes: 0

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