iOS 获取系统截屏事件

1.系统通知名称

UIApplicationUserDidTakeScreenshotNotification

以下是系统给出的说明

// This notification is posted after the user takes a screenshot (for example by pressing both the home and lock screen buttons)
UIKIT_EXTERN NSNotificationName const UIApplicationUserDidTakeScreenshotNotification NS_AVAILABLE_IOS(7_0);

2.注册监听对象

你可以写在想要的页面控制器或者直接放在AppDelegate中

[[NSNotificationCenter defaultCenter] addObserver:self
                                          selector:@selector(userDidTakeScreenshot:)
                                              name:UIApplicationUserDidTakeScreenshotNotification
                                            object:nil];

处理方法:

#pragma mark - 用户截屏通知事件
- (void)userDidTakeScreenshot:(NSNotification *)notification {
    NSLog(@"检测到截屏");
    // 手动截取当前屏幕图片
    UIImage *mainScreenshot = [[UIApplication sharedApplication].keyWindow yg_screenshot];

    /*
     自定义处理方法的代码,随意吧
    */
//添加显示
    UIImageView *imgvPhoto = [[UIImageView alloc]initWithImage:image_];
    imgvPhoto.frame = CGRectMake(self.window.frame.size.width/2, self.window.frame.size.height/2, self.window.frame.size.width/2, self.window.frame.size.height/2);
   //添加显示
    UIImageView *imgvPhoto = [[UIImageView alloc]initWithImage:mainScreenshot];
    imgvPhoto.image = mainScreenshot;
    imgvPhoto.frame = CGRectMake(kSCREEN_WIDTH * 1/6, kSCREEN_HEIGHT * 1/6, kSCREEN_WIDTH * 2/3, kSCREEN_HEIGHT * 2/3);
    //添加边框
    CALayer * layer = [imgvPhoto layer];
    layer.borderColor = [
                         [UIColor clearColor] CGColor];
    layer.borderWidth = 1.0f;
    //
    UIView *backView = [[UIView alloc]initWithFrame:CGRectMake(0, 0, kSCREEN_WIDTH, kSCREEN_HEIGHT)];
    backView.backgroundColor = [[UIColor grayColor] colorWithAlphaComponent:0.8];
    UIButton *shareBtn = [UIButton buttonWithType:UIButtonTypeSystem];
    shareBtn.titleLabel.font = [UIFont systemFontOfSize:17.0];
    [shareBtn setTintColor:[UIColor whiteColor]];
    shareBtn.frame = CGRectMake(kSCREEN_WIDTH/5,kSCREEN_HEIGHT ,kSCREEN_WIDTH*3/5,50);
    [shareBtn.layer setMasksToBounds:YES];
    [shareBtn.layer setBorderWidth:1];
    shareBtn.layer.cornerRadius = 6;
    [shareBtn setTitle:@"分享给好友" forState:UIControlStateNormal];
    shareBtn.backgroundColor = [UIColor orangeColor];
    [shareBtn addTarget:self action:@selector(shareBtn:) forControlEvents:UIControlEventTouchUpInside];
    
    [backView addSubview:imgvPhoto];
    [backView addSubview:shareBtn];
    
    UIWindow *window = [UIApplication sharedApplication].keyWindow;
    [window addSubview:backView];
    
    [UIView animateWithDuration:1.0 animations:^{
        imgvPhoto.transform = CGAffineTransformMakeScale(0.8, 0.8);
        shareBtn.transform = CGAffineTransformMakeTranslation(0, -50);
    }];
    //3秒后消失
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(6 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        [backView removeFromSuperview];
    });

}

3.获取截屏图片UIImage对象

- (UIImage *)yg_screenshot {
   
   UIGraphicsBeginImageContextWithOptions(self.bounds.size, NO, [UIScreen mainScreen].scale);
// 这个函数主要用于处理layer层，并且在layer层添加图片等图层
   如果贸然的添加图片 那么图片的边缘就会和背景图层有种分割感 不够自然
   render的意思是渲染
   所以它会使图片和背景图层在结合的地方更自然
   [self.layer renderInContext:UIGraphicsGetCurrentContext()];
   UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
   UIGraphicsEndImageContext();
   NSData *imageData = UIImageJPEGRepresentation(image, 0.5);//数值 0 - 1 之间
   image = [UIImage imageWithData:imageData];
   return image;
}

4.UIImageJPEGRepresentation 使用中存在的问题

iOS上有两种转化图片的的简单方法：
1丶UIImageJPEGRepresentation(<#UIImage * _Nonnull image#>, <#CGFloat compressionQuality#>)
参数1：图片，参数2：压缩系数
2丶UIImagePNGRepresentation(<#UIImage * _Nonnull image#>)
参数：图片
UIImageJPEGRepresentation 压缩后图片较小图片质量也无较大差异：
UIImagePNGRepresentation 压缩图片的图片较大；
日常工作中推荐使用的是UIImageJPEGRepresentation图压缩后节省内存，减少避免图片过多照成的卡顿现象。
当然如果对图片画质有极高的要求的话，还是使用UIImagePNGRepresentation。
使用UIImageJPEGRepresentation遇到的问题：
///< NSData *data = UIImageJPEGRepresentation(image, 1);偶然发现使用UIImageJPEGRepresentation 一些无背景的白色图案经过压缩之后会变成白色背景无图案的图片，因为像素低，再经压缩后，就会导致图片失真, 成为白底无图案的图片（这种情况应该不常见，但确实存在)；