When should I use the “self” keyword?

Question

When should I be using the self expression in my iphone development applications? say i have 2 fields: UITextField *text1; and NSString *str1; retained and synthesized.

when i am accessing either of these 2 fields, when should i and when should i not use self.text1 and self.str1 ?

Answer 1

self is not a keyword, it is an expression. Additionally, you use it any time you want to refer to a method or property on yourself, or yourself directly. By "yourself" I am of course, referring to the instance of the class you are operating in.

Answer 2

There are certain circumstances where it's generally discouraged to use the self.-expression to access a property. Normally you always use self for any access of a property. It's the most secure and uncomplicated way. Especially if you used retain, then memory management will be done for you.

The two exceptions from this rule:

• Any init method.
• In dealloc.

In both cases you are dealing with an partially initialized object. There are some side effects that may occur when using setters or getters here -- because they are methods and hence may be overridden.

For example, take a class A with a property foo that has been subclassed by class B. The subclass B adds an property bar and overrode the setter for foo. Now your init-method calls setFoo:, because you used self.foo = ... with some initial value. The subclass, however, also accesses the value of bar in this setter. But in this case, it may happen that bar has never been initialized and points at some arbitrary data. Calling a setter in init my cause crashes, although the probability may not be too high in your own code.