Question

Is calling [myObject performSelector:@selector(something) withObject:nil]; the same as just calling [myObject performSelector:@selector(something)];?

Answer 1

The only difference is signature of the method you intend on calling from the @selector. Use performSelector when the method takes no arguments, and use performSelector:withObject if the method takes a single argument of type id. Otherwise, they both do the exact same thing.

From the NSObject Protocol Reference:

Discussion

This method is the same as performSelector: except that you
can supply an argument for aSelector. aSelector should identify a
method that takes a single argument of type id. For methods with other
argument types and return values, use NSInvocation.

As Chuck points out, this isn’t really enforced (at least not at this point in time). The code below executed fine without any exceptions being thrown at me.

-(void)viewDidLoad
{
    [super viewDidLoad];    
    [self performSelector:@selector(foo) withObject:nil];
}
-(void)foo
{
    NSLog(@"foo!");
}

On the other hand, this version of the code did cause problems. So it doesn’t work both ways.

-(void)viewDidLoad
{
    [super viewDidLoad];    
    [self performSelector:@selector(foo)];
}
-(void)foo:(id)myParameter
{
    NSLog(@"foo!");
}