从iOS7开始Apple提供了[UIApplicationUserDidTakeScreenshotNotification]通知来告知用户已经进行截屏操作。可以监听该通知并进行相应的提示。

- (void)viewDidLoad {
    [super viewDidLoad];
    
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(userDidTakeScreenshot) name:UIApplicationUserDidTakeScreenshotNotification object:nil];
    
    [[NSNotificationCenter defaultCenter] addObserverForName:UIApplicationUserDidTakeScreenshotNotification object:nil queue:[NSOperationQueue mainQueue] usingBlock:^(NSNotification * _Nonnull note) {
        NSLog(@"检测到截屏方法2");
    }];
}

-(void)userDidTakeScreenshot{
    NSLog(@"检测到截屏方法1");
}