Using self in method call

Question

When using property/synthesize for a UITableView, UIButton, etc should self be included in the method call on that variable? Using UITableView as an example is there a difference between [self.myTableView visibleCells] and [myTableView visibleCells]? Or say [self.myImage setImage:...] and [myImage setImage:...]?

I've seen Apple code that does use self (Bubble Level) and examples in the book Beginning iPhone Development that do not use self. I'd like to understand this better, especially since using self in my UIScrollView method calls has caused erratic/buggy scrolling behavior. Thanks.

Answer 1

Using self.myTableView is another way of saying [self myTableView] (it can also be [self setMyTableView:...]; if used in an assignation statement). In other words, you're executing a method.

Using myTableView accesses the instance variable directly.

Personally, I generally prefer using the former method, since it usually frees me from manually managing memory and gives me the benefit of KVO notifications. However, there is the miniscule overhead of the extra method call, which you may wish to avoid.

Which style you choose to use is up to you, and each way has its benefits and disadvantages.

Answer 2

The difference comes down to how you define the property. For example, say you have the following:

@interface MyObject : NSObject {
   NSObject *memberVariable;
}
@property (nonatomic, retain) NSObject *memberVariable;
@end

@implementation MyObject
    @synthesize memberVariable;
@end

Specifying (nonatomic, retain) actually tells @synthesize how to create the getter and setter methods. Specifying retain causes the setter method to call retain on objects I pass to it. So, self.memberVariable = someOtherObject is equivalent to memberVariable = [someOtherObject retain];

This is also why you should never do self.memberVariable = [[NSObject alloc] init]; if you've specified retain in the property definition. alloc initializes the retain count to 1, passing the object to the setter method increases the retain count to 2.

Answer 3

This comes down to whether or not your accessor methods have custom behavior, in which case you'd always want the accessors called even from within the class, and whether you want to make sure KVO notifications are generated. If you're using stock accessors (e.g., synthesized) and it won't affect anything to access the instance variable directly from within the class, you're saving yourself a method call.