Question

Specific performance and behaviour difference using properties or accessing the ivars directly.

For Global variables, What is the difference between using this:

@interface myClass (){

    UIImageView *myView;
}

-(void)loadView{

  [super loadView];
  myView = [[UIImageView alloc] initWithFrame:CGrectMake(0,0,100,100)];
}

And doing this:

    @interface myClass (){

    }

    @property (nonatomic, strong) UIImageView *myView; 

@synthesize myView = _myView;

    -(void)loadView{

    [super loadView];
    myView = [[UIImageView alloc] initWithFrame:CGrectMake(0,0,100,100)];
    }

What benefits can we have with every approach?
What are the reasons to recommend to always uses properties?

Answer 1

In the first case, your instance variable (or ivar) myView is private to the class and cannot be accessed by another class.

In the second case, you have provided a property that allows other classes to access your ivar via synthesized accessors. The alternative to declared properties is to write your own accessor methods. The @synthesize notation does that for you.

See Apple documentation on declared properties