Need help in understanding objective c code

Question

I need some help in understanding the following code:

1. What is the meaning of '@' in @"Reload"

   button = MakeTestButton(&button_rect, @"Reload", content); [button setTarget:web_view]; [button setAction:@selector(reload:)];

2. Where I can find the definition of "@selector(reload:)"?

Answer 1

1. String constants are declared as @"some text" in objective-c. This creates an instance of NSString.
2. I recommend you read Apple's documentation on selectors. Basically, @selector(reload:) will get a pointer to the method that will be called when an objects receives a reload: message.

Answer 2

@selector is a built in primitive in the language. Think of @selector(reload:) as "the name of the method 'reload:' ". It returns a SEL, which you can then pass to a function and later use it to call the method "reload:". In the context of your code, when you click the button, the button will call [web_view reload:self].

In @"Reload", the @ means that it's an NSString instance instead of a (char const *).

Answer 3

1. The @ sign indicates to the compiler that the string is an NSString instead of a standard "C" string. This is a shortcut for creating NSString objects.

2. See http://stackoverflow.com/questions/543161/explanation-of-cocoa-selector-usage