NSMethodSignature和NSInvocation的使用（方法传多参数）

动态调用方法时会用到，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];//获得类和方法的签名 
    NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSignature]; 
    //从签名获得调用对象 
    [invocation setTarget:self]; 
    //设置target 
    [invocation setSelector:selector];//设置selector 
    NSString *returnValue = nil; 
    NSString *argument1 = @"fist"; 
    NSNumber *argument2 = [NSNumber numberWithInt:102]; 
    [invocation setArgument:&argument1 atIndex:2];//设置参数，第一个参数index为2 
    [invocation setArgument:&argument2 atIndex:3]; 
    [invocation retainArguments];//retain一遍参数 
    [invocation invoke];//调用 
    [invocation getReturnValue:&returnValue];//得到返回值，此时不会再调用，只是返回值 
    NSLog(@"return value = %@",returnValue); 
}