When to access properties with 'self'

Question

I have read a number of questions on this site about this issue, I understand the following:

self.property accesses the getter/setter method created manually or by @synthesize. Depending upon whether the property is declared as retain, copy etc. the retain count is modified correctly, for example a retained property, releases the previous value assigned the new value with 'retain' and increments the retain count by 1.

Properties are usually declared with instance variables of the same name (can be different if you make the assignment manually). This is generally because the @synthesize generated accessors use the instance variable to reference the object in memory and then perform the relevant commands.

My question is based on the fact that in many examples, self.property and property are used interchangeably for different things and I'm having troubles determining the rules. One example in the 'Recipes' example app in the Apple Docs, has the following:

self.navigationItem.title = recipe.name;
nameTextField.text = recipe.name;    
overviewTextField.text = recipe.overview;    
prepTimeTextField.text = recipe.prepTime; 

and...

self.ingredients = sortedIngredients;

Each of these properties have associated private instance variables of the same name. All are declared in the same way with 'nonatomic, retain' attributes. Each are released in dealloc...

Yet 'ingredients' is accessed through self and 'prepTimeTextField' is accessed directly.

What is the reason for the difference in access methods?

What about if I'm accessing a view's delegate? Or a core-data object which was passed to a view controller by it's previous view controller as a retained property?

Many thanks

Answer 1

Depends. If your instance variables are dumb, it's fine to access them directly. But the reason most of us like to access members through properties is that we can change something about the logic of that member, and things will still work.

For example, sometimes you'll want to change a class to load something lazily, as opposed to immediately. If you're already using properties to access your instance variable, then you can just edit the accessor method and everything should just work.

Answer 2

you almost always want to access variables using the synthesized setters/getters, even if you aren't doing anything special with them at the moment.

if as your application develops, you find that you need to be doing further validation/formatting of variables, then you can just implement the required setter/getter method, and if you have used the synthesised methods this code will get called.

this is generally a good habit to get into.

Answer 3

If you declare your property like so:

@property (nonatomic, retain) NSMutableArray *myArray;

The generated setter will automatically retain the value that gets passed in. That's why you'll see this sometimes in Apple sample code:

self.myArray= [[NSMutableArray alloc] init]:
[self.myArray release];

"[self.myArray release]" is required because the retain count is two after the first line. Releasing it insures that it is down to 1 (where it should be).

If I am just using the automatically generated setters, I will not use them when working from inside of the class. It is just much simpler for me to do:

myArray = [[NSMutableArray alloc] init];

vs. the example above.

My two cents.