在阅读内容之前删除了NSURLSessionDownloadTask文件

Question

我有以下一段代码，它已经工作了好几个月，并且刚刚开始间歇性地断开。

我在更改方式，它被调用，所以它不是完全不足为奇，但症状莫名其妙我。正在被某些请求下载的临时文件在数据读取之前似乎被删除。

我对文件属性，它的位置，并在模拟器上运行时，我甚至证实该文件包含正确的数据，而在一个断点。但是只要[NSData dataWithContentsOfFile:[location path]]或[NSData dataWithContentsOfURL:location]被调用时，文件从文件系统中删除，如果我使用的方法与NSError进去时，我得到的错误是Error Domain=NSCocoaErrorDomain Code=260 "The operation couldn’t be completed.

我的代码：

- (void)makeSoapRequest:(NSURL *)url soapRequest:(NSString *)soapRequest completionBlock:(void (^)(NSData *xmlToParse, int error))completionBlock attemptNumber:(int)attemptNumber 
{ 
    NSURLSessionConfiguration *sessionConfiguration = [NSURLSessionConfiguration defaultSessionConfiguration]; 
    NSURLSession *session = [NSURLSession sessionWithConfiguration:sessionConfiguration delegate:nil delegateQueue:nil]; 
    NSData *bodyData = [soapRequest dataUsingEncoding:NSUTF8StringEncoding]; 

    NSMutableURLRequest *request = [[NSMutableURLRequest alloc]initWithURL:url]; 
    [request setHTTPMethod:@"POST"]; 
    [request addValue:@"text/xml; charset=utf-8" forHTTPHeaderField:@"Content-Type"]; 
    [request addValue:@"" forHTTPHeaderField:@"SOAPAction"]; 
    [request addValue:[NSString stringWithFormat:@"%d",(int)[bodyData length]] forHTTPHeaderField:@"Content-Length"]; 
    [request setHTTPBody:bodyData]; 

    NSURLSessionDownloadTask *downloadTask = [session downloadTaskWithRequest:request completionHandler:^(NSURL *location, NSURLResponse *response, NSError *error) { 
    if (!(location == nil)) 
    { 
     dispatch_async(dispatch_get_main_queue(), ^{ 
      if (error) 
      { 
       NSLog(@"nsurl error was: %@", error); 
      } 
      else 
      { 
       NSError* errorObj; 
       NSString *path = [location path]; 

       NSDictionary* attribs = [[NSFileManager defaultManager] attributesOfItemAtPath:path error:&errorObj]; 
       NSData *xmlData= [NSData dataWithContentsOfFile:path options:NSDataReadingMappedIfSafe error:&errorObj]; 
       if (errorObj != nil) { 
        NSLog(@"Attributes of file: %@", attribs); 
        NSLog(@"Error reading the downloaded data, error was: %@", errorObj); 
       } 
       completionBlock(xmlData, 0); 
       return; 
      } 
     }); 
    } 
    else 
    { 
     if (error) 
     { 
      dispatch_async(dispatch_get_main_queue(), ^{ 
       completionBlock(nil,-1); 
      }); 
     } 
     else 
     { 
      dispatch_async(dispatch_get_main_queue(), ^{ 
       completionBlock(nil,-1); 
      }); 
     } 
    } 
}]; 
[downloadTask resume]; 
} 

我属性打印：

Attributes of file: { 
NSFileCreationDate = "2016-11-23 13:15:00 +0000"; 
NSFileExtensionHidden = 0; 
NSFileGroupOwnerAccountID = 501; 
NSFileGroupOwnerAccountName = mobile; 
NSFileModificationDate = "2016-11-23 13:15:00 +0000"; 
NSFileOwnerAccountID = 501; 
NSFileOwnerAccountName = mobile; 
NSFilePosixPermissions = 384; 
NSFileReferenceCount = 1; 
NSFileSize = 947; 
NSFileSystemFileNumber = 534146; 
NSFileSystemNumber = 16777218; 
NSFileType = NSFileTypeRegular; 
} 

错误日志：

2016-11-23 13:27:43.285 GCMMobile[2780:829109] Error reading the downloaded data, error was: Error Domain=NSCocoaErrorDomain Code=260 "The operation couldn’t be completed. (Cocoa error 260.)" UserInfo=0x1704605c0 {NSFilePath=/private/var/mobile/Containers/Data/Application/BF6BE574-AA1A-492E-A1DD-04334F33E2D7/tmp/CFNetworkDownload_VHyKp6.tmp, NSUnderlyingError=0x17024ce10 "The operation couldn’t be completed. No such file or directory"} 

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Answer 1

问题是，您正在从NSURLSessionDownloadTask完成处理程序返回之前移动或打开下载的文件。由于documentation状态：

你必须移动这个文件或打开它为您完成 处理程序返回前阅读。否则，文件被删除，数据丢失。

通过调度到主队列并返回您将文件读取代码推迟到某个无限期的时间。您应该在完成处理程序本身中移动或打开文件，然后才可以将其分派到另一个队列以供后续处理。