NSMethodSignature和NSInvocation的使用

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);
} 

另外一个例子: