从URL获取图像不清晰

Question

I am working on one application where i have to load images from server.

我正在尝试从应用商店的链接加载应用程序屏幕截图。 我得到了图像，但不是那么清晰和清晰。我正在后台获取图像，一切正常。但是生成的图像看起来有点模糊。我正在视网膜显示器上测试此图像。任何人都知道为什么会发生这种情况。任何解决方案都会有所帮助。

谢谢

这是我用于图像加载的代码：

// This will create the imageview with required frame & use the url to load the image
-(void)loadAppsScreenShots:(int)i Frame:(CGRect)frame withImageUrl:(NSString *)urlStr
{
    UIImageView *appImageView = [[UIImageView alloc] init];
    frame.origin.x = 0;
    appImageView.frame = frame;
    appImageView.tag = i;
    sharedImageCache = [ImageCache sharedImageCacheInstance];
    UIImage *image1 = [sharedImageCache getCachedImage:[NSString stringWithFormat:@"%@",urlStr]];
    if (image1==nil) 
    {       
        // Show indicator till image loads     
        UIActivityIndicatorView *indiView = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhite];
        indiView.center = CGPointMake(appImageView.frame.size.width/2, appImageView.frame.size.height/2);
        [appImageView addSubview:indiView];
        [indiView startAnimating];
        indiView.hidden = FALSE;
        // Show label indicating image loading process 
        UILabel *loadingLbl = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, 200, 25)];
        loadingLbl.text = @"";//@"Please wait...";
        loadingLbl.center = CGPointMake(appImageView.frame.size.width/2 + 5, appImageView.frame.size.height/2 + 23);
        loadingLbl.font = [UIFont fontWithName:@"Helvetica-Bold" size:15.0f];
        loadingLbl.textAlignment = UITextAlignmentCenter;
        loadingLbl.backgroundColor = [UIColor clearColor];
        loadingLbl.textColor = [UIColor whiteColor];
        [appImageView addSubview:loadingLbl];
        [appImageView sendSubviewToBack:loadingLbl];
        loadingLbl.hidden = FALSE;
        // Dictionalry to get all objects & pass it to method where we load the data
        NSMutableDictionary *dict = [[NSMutableDictionary alloc] init];
        [dict setObject:appImageView forKey:@"imageView"];
        if (urlStr != nil) {
            [dict setObject:urlStr forKey:@"url"];
        }
        [dict setObject:indiView forKey:@"indi"];
        [dict setObject:loadingLbl forKey:@"loadingLbl"];
        [self performSelectorInBackground:@selector(loadImageFromURLAndSaveInDocDir:) withObject:dict];
    }
    else 
    {
        appImageView.image = image1;
    }
    [[appView viewWithTag:i] addSubview:appImageView];
    [appView bringSubviewToFront:appImageView];
    appImageView.contentMode = UIViewContentModeScaleAspectFit;
    appImageView=nil;
}

-(void)loadImageFromURLAndSaveInDocDir:(NSMutableDictionary *)dict
{
    @autoreleasepool 
    {
        UIImageView *cellImageViewObj = [dict objectForKey:@"imageView"];
        NSString *url;
        UIActivityIndicatorView *indiview = [dict objectForKey:@"indi"];
        UILabel *Lbl = [dict objectForKey:@"loadingLbl"];        
        if ([dict objectForKey:@"url"]) 
        {
            url = [dict objectForKey:@"url"];
            // fetch the data
            NSURL *imgURL = [NSURL URLWithString:url];
            NSData *imgData = [NSData dataWithContentsOfURL:imgURL];
            NSString *filename = [Utils getFileNameFromURL:url];
            // Cache the image
            [sharedImageCache cacheImage:[NSString stringWithFormat:@"%@",filename] :imgData];
            UIImage *image1 = [[UIImage alloc] initWithData:imgData];
            cellImageViewObj.image = image1;
            image1=nil;
        }
        else {
            url = @"";
        }
        // set the content mode & hide the indicator & label
        cellImageViewObj.contentMode = UIViewContentModeScaleAspectFit;
        [indiview stopAnimating];
        indiview.hidden = TRUE;
        Lbl.hidden = TRUE;
        dict = nil;
    }
}

我做错了什么。

Answer 1

问题是您以自然大小显示图像。在视网膜设备上，您需要的图像宽度和高度是它们所绘制视图的两倍和两倍。

假设图像是 200x200，您将以 100x100 的视图显示它。 正确的方法是：

• 获取数据的 CGImageRef

• 使用以下方法创建 UIImage，比例为 2(对于视网膜(

  • (UIImage *(imageWithCGImage：(CGImageRef(imageRef scale：(CGFloat(scale orientation：(UIImageOrientation(orientation

结果是一个大小为 100x100 但比例为 2 的图像。

---

也就是说，由于您指定了"UIViewContentModeScaleAspectFit"，因此您可能只获取 200x200 的图像并将其关闭到 UIImageView，但在这种情况下，您必须强制图像视图的帧大小为 100x100。

Answer 2

如果图像大小与 imageview 不同，则可以根据视图按比例缩放服务器图像。

- (UIImage *)imageByScalingProportionallyToSize:(CGSize)targetSize;
- (UIImage *)imageByScalingProportionallyToSize:(CGSize)targetSize {
    UIImage *sourceImage = self;
    UIImage *newImage = nil;
    CGSize imageSize = sourceImage.size;
    CGFloat width = imageSize.width;
    CGFloat height = imageSize.height;
    CGFloat targetWidth = targetSize.width;
    CGFloat targetHeight = targetSize.height;
    CGFloat scaleFactor = 0.0;
    CGFloat scaledWidth = targetWidth;
    CGFloat scaledHeight = targetHeight;
    CGPoint thumbnailPoint = CGPointMake(0.0,0.0);
    if (CGSizeEqualToSize(imageSize, targetSize) == NO) {
        CGFloat widthFactor = targetWidth / width;
        CGFloat heightFactor = targetHeight / height;
        if (widthFactor < heightFactor) 
            scaleFactor = widthFactor;
        else
            scaleFactor = heightFactor;
        scaledWidth  = width * scaleFactor;
        scaledHeight = height * scaleFactor;
        // center the image
        if (widthFactor < heightFactor) {
            thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5; 
        } else if (widthFactor > heightFactor) {
            thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;
        }
    }

    // this is actually the interesting part:
    UIGraphicsBeginImageContext(targetSize);
    CGRect thumbnailRect = CGRectZero;
    thumbnailRect.origin = thumbnailPoint;
    thumbnailRect.size.width  = scaledWidth;
    thumbnailRect.size.height = scaledHeight;
    [sourceImage drawInRect:thumbnailRect];
    newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    if(newImage == nil) NSLog(@"could not scale image");

    return newImage ;
}