iPhone是否压缩保存在我的应用程序文档目录中的图像？

我们正在缓存从服务器下载的图像。我们从ASIHTTPRequest回调获取数据，如下所示：

#pragma mark ASIHTTPRequest callback
-(void)imageDownloadFinished:(ASIHTTPRequest*)aRequest
{
    NSString* fileName = aRequest.url.path.lastPathComponent; 
    [self imageDidArrive:[aRequest responseData] forFileName:fileName];
}

 NSArray *paths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES);
 NSString *documentsDirectory = [paths objectAtIndex:0] ; 
 NSString* folder = [[documentsDirectory stringByAppendingPathComponent:@"flook.images"] retain];
        NSString* fileName = [folder stringByAppendingFormat:@"/%@", aBaseFilename];

 BOOL writeSuccess = [anImageData writeToFile:fileName atomically:NO];

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES);
 NSString *documentsDirectory = [paths objectAtIndex:0] ; 
 NSString* folder = [[documentsDirectory stringByAppendingPathComponent:@"flook.images"] retain];
        NSString* fileName = [folder stringByAppendingFormat:@"/%@", aBaseFilename];

 image = [UIImage imageWithContentsOfFile:fileName];

我们将图像数据写入本地存储器，如下所示：

#pragma mark ASIHTTPRequest callback
-(void)imageDownloadFinished:(ASIHTTPRequest*)aRequest
{
    NSString* fileName = aRequest.url.path.lastPathComponent; 
    [self imageDidArrive:[aRequest responseData] forFileName:fileName];
}

 NSArray *paths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES);
 NSString *documentsDirectory = [paths objectAtIndex:0] ; 
 NSString* folder = [[documentsDirectory stringByAppendingPathComponent:@"flook.images"] retain];
        NSString* fileName = [folder stringByAppendingFormat:@"/%@", aBaseFilename];

 BOOL writeSuccess = [anImageData writeToFile:fileName atomically:NO];

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES);
 NSString *documentsDirectory = [paths objectAtIndex:0] ; 
 NSString* folder = [[documentsDirectory stringByAppendingPathComponent:@"flook.images"] retain];
        NSString* fileName = [folder stringByAppendingFormat:@"/%@", aBaseFilename];

 image = [UIImage imageWithContentsOfFile:fileName];

下载的图像总是预期大小，大约45-85KB

稍后，我们从缓存中读取图像，如下所示：

#pragma mark ASIHTTPRequest callback
-(void)imageDownloadFinished:(ASIHTTPRequest*)aRequest
{
    NSString* fileName = aRequest.url.path.lastPathComponent; 
    [self imageDidArrive:[aRequest responseData] forFileName:fileName];
}

 NSArray *paths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES);
 NSString *documentsDirectory = [paths objectAtIndex:0] ; 
 NSString* folder = [[documentsDirectory stringByAppendingPathComponent:@"flook.images"] retain];
        NSString* fileName = [folder stringByAppendingFormat:@"/%@", aBaseFilename];

 BOOL writeSuccess = [anImageData writeToFile:fileName atomically:NO];

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES);
 NSString *documentsDirectory = [paths objectAtIndex:0] ; 
 NSString* folder = [[documentsDirectory stringByAppendingPathComponent:@"flook.images"] retain];
        NSString* fileName = [folder stringByAppendingFormat:@"/%@", aBaseFilename];

 image = [UIImage imageWithContentsOfFile:fileName];

偶尔，从缓存读取返回的图像要小得多，因为它们要压缩得多——大约5-10KB。操作系统对我们这样做了吗

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编辑-结果是我们正在下载小图像，因此问题不在iPhone上

如果我正确读取了您的代码，您使用的是NSData方法writeToFile:atomicaly:写入文件。它对NSData对象的内容进行精确的逐字节写入

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NSData对象似乎是直接从HTTP响应的内容创建的，因此答案是否定的，不应该发生任何压缩。

我们有了解决方案。当手机在3G网络上运行时，O2善意地介入并对我们的图像应用额外的JPG压缩，使它们看起来格外可怕

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看看这个。

顺便说一句，我正在调试不是我自己的代码，所以我很愿意相信我错过了一些东西！anImageData是如何创建的？例如，您是否使用UIImageJPEGresentation？它由ASIHTTPRequest回调提供，以便在图像下载时成功：pragma mark ASIHTTPRequest回调-voidimageDownloadFinished:ASIHTTPRequest*aRequest；{NSString*fileName=aRequest.url.path.lastPathComponent；[self-imagedidarrim:[aRequest-responseData]forFileName:fileName]；}并且图像是JPGs。肯定发生了什么事情！但也许它在我尚未发现的代码的某个角落。