iOS 监听用户截屏并获取

集团考勤最新的意见反馈需求，参照了京东的截屏反馈。
重点就是如何监听到 用户触发了系统级的截屏，并获取到当前截屏图片。

监听到用户截屏后，有两种处理方式：

• 方式一：模拟用户的截屏动作，用layer 去绘制当前app的window 展示的内容，然后进行图像处理（比较复杂），获得UIImage
• 方式二：在截屏后，去访问用户相册，拿到用户相册的最后一张图片，判断是不是截屏，然后采用。

一、注册监听通知 -- userDidTakeScreenshot

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

二、监听用户截屏动作，并处理layer（方式一）

－(void)userDidTakeScreenshot:(NSNotification *)notification
{
    NSLog(@"检测到截屏");
    //人为截屏, 模拟用户截屏行为, 获取所截图片
    UIImage *image_ = [self imageWithScreenshot];
    //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);
    //添加边框
    CALayer * layer = [imgvPhoto layer];
    layer.borderColor = [
                         [UIColor whiteColor] CGColor];
    layer.borderWidth = 5.0f;
    //添加四个边阴影
    imgvPhoto.layer.shadowColor = [UIColor blackColor].CGColor;
    imgvPhoto.layer.shadowOffset = CGSizeMake(0, 0);
    imgvPhoto.layer.shadowOpacity = 0.5;
    imgvPhoto.layer.shadowRadius = 10.0;
    //添加两个边阴影
    imgvPhoto.layer.shadowColor = [UIColor blackColor].CGColor;
    imgvPhoto.layer.shadowOffset = CGSizeMake(4, 4);
    imgvPhoto.layer.shadowOpacity = 0.5;
    imgvPhoto.layer.shadowRadius = 2.0;
    [self.window addSubview:imgvPhoto];
}

三、处理截屏图像（方式一）

- (UIImage *)imageWithScreenshot
{
    NSData *imageData = [self dataWithScreenshotInPNGFormat];
    return [UIImage imageWithData:imageData];
}

- (NSData *)dataWithScreenshotInPNGFormat
{
    CGSize imageSize = CGSizeZero;
    UIInterfaceOrientation orientation = [UIApplication sharedApplication].statusBarOrientation;
    if (UIInterfaceOrientationIsPortrait(orientation))
        imageSize = [UIScreen mainScreen].bounds.size;
    else
        imageSize = CGSizeMake([UIScreen mainScreen].bounds.size.height, [UIScreen mainScreen].bounds.size.width);

    UIGraphicsBeginImageContextWithOptions(imageSize, NO, 0);
    CGContextRef context = UIGraphicsGetCurrentContext();
    for (UIWindow *window in [[UIApplication sharedApplication] windows])
    {
        CGContextSaveGState(context);
        CGContextTranslateCTM(context, window.center.x, window.center.y);
        CGContextConcatCTM(context, window.transform);
        CGContextTranslateCTM(context, -window.bounds.size.width * window.layer.anchorPoint.x, -window.bounds.size.height * window.layer.anchorPoint.y);
        if (orientation == UIInterfaceOrientationLandscapeLeft)
        {
            CGContextRotateCTM(context, M_PI_2);
            CGContextTranslateCTM(context, 0, -imageSize.width);
        }
        else if (orientation == UIInterfaceOrientationLandscapeRight)
        {
            CGContextRotateCTM(context, -M_PI_2);
            CGContextTranslateCTM(context, -imageSize.height, 0);
        } else if (orientation == UIInterfaceOrientationPortraitUpsideDown) {
            CGContextRotateCTM(context, M_PI);
            CGContextTranslateCTM(context, -imageSize.width, -imageSize.height);
        }
        if ([window respondsToSelector:@selector(drawViewHierarchyInRect:afterScreenUpdates:)])
        {
            [window drawViewHierarchyInRect:window.bounds afterScreenUpdates:YES];
        }
        else
        {
            [window.layer renderInContext:context];
        }
        CGContextRestoreGState(context);
    }

    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return UIImagePNGRepresentation(image);
}

四、方式二：获取用户最后一张图片

static NSTimeInterval const latestAssetFetchInterval = 10;

@interface AJUserPhotoFetchManager ()

@property (nonatomic, strong, nullable) NSDate *lastAssetcreationDate;
@end

static NSString * const kLastAssetcreationDateKey = @"kLastAssetcreationDateKey";
@implementation AJUserPhotoFetchManager

#pragma mark - 单例方法
static AJUserPhotoFetchManager *sharedInstance;
+ (id)allocWithZone:(struct _NSZone *)zone
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        sharedInstance = [super allocWithZone:zone];
        sharedInstance.lastAssetcreationDate = [[NSUserDefaults standardUserDefaults] objectForKey:kLastAssetcreationDateKey];
    });
    
    return sharedInstance;
}

+ (AJUserPhotoFetchManager *)sharedUserPhotoFetchManager
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        sharedInstance = [[AJUserPhotoFetchManager alloc]init];
        sharedInstance.lastAssetcreationDate = [[NSUserDefaults standardUserDefaults] objectForKey:kLastAssetcreationDateKey];
    });
    return sharedInstance;
}


/** 点击“＋”号的时候获取相册列表，获取最新保存的一张图片。
  * 根据图片保存时间，与当前时间戳进行计算，获得间隔时间。从而判断是否是需求的时间间隔。（时间间隔自定义）
 */
- (void)fetchLatestPhotoInTimeIntervalWithCompletion:(void (^)(UIImage *result, NSDictionary *info))completion{
    // 此处不能主动获取权限，在用户同意的情况下可以去获取
    PHAuthorizationStatus status = [PHPhotoLibrary authorizationStatus];
    if (status == PHAuthorizationStatusAuthorized) {
        
//        AJUserPhotoFetchManager *sharedUserPhotoFetchManager = [AJUserPhotoFetchManager sharedUserPhotoFetchManager];
        PHAsset *latestAsset = [self fetchLatestPhotoAsset];
        NSDate *nowDate = [NSDate date];
        NSTimeInterval timeInterval = [nowDate timeIntervalSinceDate:latestAsset.creationDate];// 创建时间距离的时间间隔
        if (timeInterval > latestAssetFetchInterval) { // 超出时间了
            return;
        }
        // 对一张图片10s内两次获取，虽然是同一张图片，系统回调的图片结果地址不一致。 
        // 阅读了相关博客也不建议用回调的info里面字段作判断, 所以这里采用的图片的时间戳
        if (self.lastAssetcreationDate && [self.lastAssetcreationDate compare:latestAsset.creationDate] != NSOrderedAscending) { // 上次已经获取过了
            return;
        }
        
        PHImageRequestOptions *options = [[PHImageRequestOptions alloc] init];
        options.deliveryMode = PHImageRequestOptionsDeliveryModeHighQualityFormat;
        
        [[PHImageManager defaultManager] requestImageForAsset:latestAsset targetSize:UIScreen.mainScreen.bounds.size contentMode:PHImageContentModeAspectFit options:options resultHandler:^(UIImage *result, NSDictionary *info) {
            self.lastAssetcreationDate = latestAsset.creationDate;
            [[NSUserDefaults standardUserDefaults] setObject:latestAsset.creationDate forKey:kLastAssetcreationDateKey];
            completion(result, info);
        }];
    }
}

- (PHAsset *)fetchLatestPhotoAsset{

    PHFetchOptions *options = [[PHFetchOptions alloc]init];
    if (@available(iOS 9.0, *)) {
        options.fetchLimit = 1;
    }
    options.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:@"creationDate" ascending:NO]];
    PHFetchResult *assetsFetchResults = [PHAsset fetchAssetsWithOptions:options];
    return assetsFetchResults.firstObject;
}

+ (void)requestAuthorization:(void (^)(PHAuthorizationStatus))handler{
    [PHPhotoLibrary requestAuthorization:handler];
}