Objective-C中呼叫函式的方法是“訊息傳遞”，這個和普通的函式呼叫的區別是，你可以隨時對一個物件傳遞任何訊息，而不需要在編譯的時候宣告這些方法。所以Objective-C可以在runtime的時候傳遞訊息。

主要用到：SEL和@selector，當然還有performSelector

看例子：

先是三個函式：

1. -(void)CallBack0  
2. {  
3.     NSLog(@"CallBack0");  
4. }  
5. -(void)CallBack1:(int)a  
6. {  
7.     NSLog(@"CallBack1:a=%i",a);  
8. }  
9. -(void)CallBack2:(
   int)a b:(int)b  
10. {  
11.     NSLog(@"CallBack2:a=%i,b=%i",a,b);  
12. }  

1. [self performSelector:@selector(CallBack0)];  
2. [self performSelector:@selector(CallBack1:) withObject:1];  
3. [self performSelector:@selector(CallBack2:b:) withObject:1 withObject:2];  

1. NSString *[email protected]
   "CallBack0";  
2. SEL faSelector=NSSelectorFromString(a);  
3. [self performSelector:faSelector];  
4. NSString *[email protected]"CallBack1:";  
5. SEL fbSelector=NSSelectorFromString(b);  
6. [self performSelector:fbSelector withObject:1];  
7. NSString *[email protected]"CallBack2:b:";  
8. SEL fcSelector=NSSelectorFromString(c);  
9. [self performSelector:fcSelector withObject:1 withObject:2];