Objective-C Class Initializer

This post is the first in a series of posts about Objective-c / Cocoa programming tips.
As you should already known, a basic initializer for an objective-c class looks like this:

- (id)init {
    if (self = [super init]) {
        /* Put your code here */
    return self;

But what does it mean?
Firstly, the minus sign tell us it is an instance method. It can only be called on an already allocated object.
Secondly, your initializer returns an id object. An id object is more flexible to use than a pointer, it can refer to any kind of object. It also allows to call method that aren't on the interface declaration, without getting a warning from the compiler.
Thirdly, we put the result of the call to the super initializer in our self pointer. This pointer represents the object we are currently initializing. As a matter of fact, in most cases we don't need to to change the self value. It is only a security in case the super initializer would return something else than the object to be initialized. I don't know any class where it can happen, but it's better to be careful.
Finally, if the call to the super initializer fail, that is to say if it returns a nil pointer value, the initialization code isn't executed and nil is returned by this method.


As I am writing from my phone, today's article will be short.

When creating your cocoa's application, you will often be asked to set a delegate object. This is not specific to objective-c development.

I will take a simple example : a table. There exists two ways two create cells in a table. The first one is active, we tell the table to add a cell, and we do so for each cell. The second one is passive. When the table want to be draw or updated, he ask our code what it should do.

How many rows should I have? What cell should I display there? What should I do when my cell is selected?

That is delegation. The answers are given by an instance of a class implementing an interface. This object is the delegate.

As a matter of fact, in iOS development, a UITableView use a double delegation. The delegate defines the behavior while the datasource defines the content.