iOS 关于监听手机截图,UIView生成UIImage, UIImage裁剪与压缩的总结

来源：cnblogs　　作者：甘林梦　　时间：2018/12/27 9:36:08　　对本文有异议

一. 关于监听手机截图

1. 背景: 发现商品的售价页总是被人转发截图,为了方便用户添加截图分享的小功能

首先要注册用户截屏操作的通知

- (void)viewDidLoad {
    [super viewDidLoad];
    //注册用户的截屏操作通知
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(userDidTakeScreenshot:)
                                                 name:UIApplicationUserDidTakeScreenshotNotification object:nil];
}

之后人为截图

// 截屏响应
- (void)userDidTakeScreenshot:(NSNotification *)notification
{
    //人为截屏, 模拟用户截屏行为, 获取所截图片
    _screenshotImg = [UIutils imageWithScreenshot]; // 这里封装了一下 获得图片就可以取分享啦
    DhshareActionSheetScreenshot *shareAlert = [[DhshareActionSheetScreenshot alloc] init];
    [shareAlert showWithImg:_screenshotImg];
}

人为截图,在这里可以对图片进行一些操作,比如添加自己的APP二维码啥的类似微博

/**
 *  截取当前屏幕 并修改
 */
+ (UIImage *)imageWithScreenshot
{
    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  image;
}

当然最后不要忘记注销通知,这里要注意,根据需求来,如果商品详情页又可以跳转到别的商品详情页最好这样注销,

避免跳到别的商品详情页多次截图

- (void)viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];
    [[NSNotificationCenter defaultCenter] removeObserver:self name:UIApplicationUserDidTakeScreenshotNotification object:nil];
}

二. UIView生成UIImag

UIView生成UIImage 时可以转一下jpg格式,这样图片不会太大具体参数可以百度,屏幕密度我一般采用0.7;

// UIView生成图片
+(UIImage*)convertViewToImage:(UIView*)v{
    CGSize s = v.bounds.size;
    // 下面方法，第一个参数表示区域大小。第二个参数表示是否是非透明的。如果需要显示半透明效果，需要传NO，否则传YES。第三个参数就是屏幕密度了
    //    NSLog(@"[UIScreen mainScreen].scale-%f",[UIScreen mainScreen].scale);
    // 3.0 高清图 分享不了 用2.0即可 或者分享的时候压缩图片
    UIGraphicsBeginImageContextWithOptions(s, YES, [UIScreen mainScreen].scale);
    [v.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage*image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    
    NSData * data = UIImageJPEGRepresentation(image, 0.7);
    UIImage* imagelast = [UIImage imageWithData:data];
    
    return imagelast;
}

三. UIImage的裁剪

// 图片裁剪
+ (UIImage *)ct_imageFromImage:(UIImage *)image inRect:(CGRect)rect{
    
    //把像 素rect 转化为 点rect（如无转化则按原图像素取部分图片）
    CGFloat scale = [UIScreen mainScreen].scale;
    CGFloat x= rect.origin.x*scale,y=rect.origin.y*scale,w=rect.size.width*scale,h=rect.size.height*scale;
    CGRect dianRect = CGRectMake(x, y, w, h);
    
    //截取部分图片并生成新图片
    CGImageRef sourceImageRef = [image CGImage];
    CGImageRef newImageRef = CGImageCreateWithImageInRect(sourceImageRef, dianRect);
    UIImage *newImage = [UIImage imageWithCGImage:newImageRef scale:[UIScreen mainScreen].scale orientation:UIImageOrientationUp];
    
    NSData * data = UIImageJPEGRepresentation(newImage, 0.7);
    UIImage* imagelast = [UIImage imageWithData:data];
    return imagelast;
}

四. UIImage的压缩

分享图片时根据分享的应用不同对图片大小是有限制的,微信是10M,但是qq小一些,

另外小程序分享的话也是有限制的128Kb,当截图裁剪后无法满足时就需要压缩一下

先是密度压缩然后大小压缩,一般都可以解决的

// 图片压缩
+ (UIImage *)compressImage:(UIImage *)image toByte:(NSUInteger)maxLength {
    // Compress by quality
    CGFloat compression = 0.7;
    //UIImage转换为NSData
    NSData *data = UIImageJPEGRepresentation(image, compression);
    if (data.length < maxLength){
        return image;
    }
    CGFloat max = 1;
    CGFloat min = 0;
    for (int i = 0; i < 6; ++i) {
        compression = (max + min) / 2;
        data = UIImageJPEGRepresentation(image, compression);
        if (data.length < maxLength * 0.9) {
            min = compression;
        } else if (data.length > maxLength) {
            max = compression;
        } else {
            break;
        }
    }
    UIImage *resultImage = [UIImage imageWithData:data];
    if (data.length < maxLength){
        return resultImage;
    }
    // Compress by size
    NSUInteger lastDataLength = 0;
    while (data.length > maxLength && data.length != lastDataLength) {
        lastDataLength = data.length;
        CGFloat ratio = (CGFloat)maxLength / data.length;
        CGSize size = CGSizeMake((NSUInteger)(resultImage.size.width * sqrtf(ratio)),
                                 (NSUInteger)(resultImage.size.height * sqrtf(ratio))); // Use NSUInteger to prevent white blank
        UIGraphicsBeginImageContext(size);
        [resultImage drawInRect:CGRectMake(0, 0, size.width, size.height)];
        resultImage = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
        data = UIImageJPEGRepresentation(resultImage, compression);
    }
    return resultImage;
}