動(dòng)態(tài)調(diào)用方法時(shí)會(huì)用到，例子 

-(NSString *)myMethod:(NSString *)param1 withParam2:(NSNumber *)param2 
{ 
    NSString *result = @"objc"; 
    NSLog(@"par = %@",param1); 
    NSLog(@"par 2 = %@",param2); 
    return result; 
} 


-(void)invokeMyMethodDynamically 
{ 
    SEL selector = @selector(myMethod:withParam2:); 
    NSMethodSignature *methodSignature = [[self class] instanceMethodSignatureForSelector:selector];//獲得類和方法的簽名 
    NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSignature]; 
    //從簽名獲得調(diào)用對(duì)象 
    [invocation setTarget:self]; 
    //設(shè)置target 
    [invocation setSelector:selector];//設(shè)置selector 
    NSString *returnValue = nil; 
    NSString *argument1 = @"fist"; 
    NSNumber *argument2 = [NSNumber numberWithInt:102]; 
    [invocation setArgument:&argument1 atIndex:2];//設(shè)置參數(shù)，第一個(gè)參數(shù)index為2 
    [invocation setArgument:&argument2 atIndex:3]; 
    [invocation retainArguments];//retain一遍參數(shù) 
    [invocation invoke];//調(diào)用 
    [invocation getReturnValue:&returnValue];//得到返回值，此時(shí)不會(huì)再調(diào)用，只是返回值 
    NSLog(@"return value = %@",returnValue); 
} 

另外一個(gè)例子: