navigationBarrespondsToSelector方法 判断对象是否接受到了某个方法

 if ([self.navigationController.navigationBarrespondsToSelector:@selector(setBackgroundImage:forBarMetrics:)]) {

        [self.navigationController.navigationBarsetBackgroundImage:[UIImageimageNamed:@"nav_bg.png"] forBarMetrics:UIBarMetricsDefault];

    }

 

 

[self.navigationController.navigationBarrespondsToSelector:@selector(setBackgroundImage:forBarMetrics:)]

判断当前的对象self 的navigationController 是否响应了方法(消息) setBackgroundImage:forBarMetrics: