Question

I have been wondering about the following lines of code

[self performSelector:@selector(myMethod) withObject:self afterDelay:1.0];
[self performSelector:@selector(myMethod) withObject:nil afterDelay:1.0];

1. Whats the difference between the above 2 lines of code.
2. When should we set object as nil and when should we set object as self?

In most cases I have noticed the object to be set as nil.

Answer 1

The difference is whether or not you are passing an object to the selector. All the selector is doing is describing a method.

[self performSelector:@selector(myMethod) withObject:nil afterDelay:1.0];

is different from:

[self performSelector:@selector(myMethod:usingThis:) withObject:nil afterDelay:1.0];

Now if you want the selector (i.e. method) to work on some object that you pass in, say an Array, Dictionary, or class. You use withObject. As in:

[self performSelector:@selector(myMethod:) withObject:myDictionary afterDelay:1.0];

-(void)myMethod:(NSDictionary*)dictionary
{
// Do something with object
}

You could pass in anything including a reference to the current class (e.g. self), as you did in your example.