do I have to create a new object or can I use a method param?

So let's say I have this method that responds to a button event

- (void) myMethod: (id) sender

Is it better 开发者_如何学编程to use directly the function param?

NSLog(@"The sender tag is %d",sender.tag);

Or is it better to create a new object?

UIButton* myButton = (UIButton*) sender;
NSLog(@"The sender tag is %d",myButton.tag);

Why?

I've seen in tutorials that the preferred way in objective-c is the second one. But, in cases where you don't need to know the type of the sender and just access its properties/methods it should be Ok to use the first way. Am I missing something?

When you say UIButton* myButton = (UIButton*) sender;, you are not making a new object. You are simply making a new handle (pointer) to the sender object, and explicitly telling the compiler that it is a UIButton.

This means that you can call UIButton methods on it without having the compiler complain that they might not exist.

From a memory point of view, you should assume it makes no difference at all. The compiler is probably smart enough to not make you a new pointer anyway, and even if it did, it's going to be 4 bytes or so, which is not worth worrying about.

You're not missing anything and this isn't a particularly important issue. You have a few options:

NSLog(@"%d", sender.tag);

Sometimes that will produce warnings when compiling, depending on the type of the method parameter.

NSLog(@"%d", ((UIButton *)sender).tag);

Or finally:

UIButton *button = (UIButton *)sender;
NSLog(@"%d", button.tag);

(These all basically do the same thing, so it's mostly a matter of preference.)

If the sender is always UIButton, I would declare method as

- (void) myMethod: (UIButton*) sender

because it practically yield the same effect to pointer type casting. It also saves you one line of code.