NSURLSession 下载任务 - 进度条问题

Question

我正在处理一个非 ARC 项目，我必须在其中下载视频，下载后我将显示它们。我正在使用 NSURLSession 下载它。

问题在进度条中。当我开始下载第四个文件时，我可以通过进度条正确下载前两个或三个文件，进度条没有正确更新，但文件与最后删除的文件一起下载。

再次删除并再次下载时会崩溃

尝试在已失效的会话中创建任务

 - (void)startOrPauseDownloadingSingleFile : (UIButton *)sender
  {
    self.part_id_Value = self.part_id;
    m_Web getIconPathForAnimation:self.part_id];

     [UIApplication sharedApplication].networkActivityIndicatorVisible = YES;
      NSURL *urlVideo=[NSURL URLWithString:self.NonInteractiveMP4URL];
      NSString *strlastcomponent=[urlVideo lastPathComponent];


      FileDownloadInfo *fdi = [[FileDownloadInfo alloc] initWithFileTitle:strlastcomponent andDownloadSource:[NSString stringWithFormat:@"%@",urlVideo]];



        if (!fdi.isDownloading)
        {
            // Check if should create a new download task using a URL, or using resume data.


            if (fdi.taskIdentifier == -1)
            {
             **Getting Crash Here**

                fdi.downloadTask = [self.session downloadTaskWithURL:[NSURL URLWithString:fdi.downloadSource]];
            }
            else
            {
                fdi.downloadTask = [self.session downloadTaskWithResumeData:fdi.taskResumeData];
            }

            // Keep the new taskIdentifier.
            fdi.taskIdentifier = fdi.downloadTask.taskIdentifier;

            // Start the download.
            [fdi.downloadTask resume];

            // Indicate for each file that is being downloaded.
            fdi.isDownloading = YES;
        }
    }

我的下载和更新进度条的方法 -

- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite
 {
   double Progress = (double)totalBytesWritten / (double)totalBytesExpectedToWrite;
   NSLog(@"Progressview progress : %f",Progress);

if (totalBytesExpectedToWrite == NSURLSessionTransferSizeUnknown)
{
    NSLog(@"Unknown transfer size");
}
else
{
    [self performSelectorOnMainThread:@selector(updateProgress:) withObject:[NSString stringWithFormat:@"%f",Progress] waitUntilDone:NO];
 }
}

- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location
 {
 NSError *error;
 NSFileManager *fileManager = [NSFileManager defaultManager];
 NSString *destinationFilename = downloadTask.originalRequest.URL.lastPathComponent;
 NSURL *destinationURL = [self.docDirectoryURL URLByAppendingPathComponent:destinationFilename];

 if ([fileManager fileExistsAtPath:[destinationURL path]])
 {
    [fileManager removeItemAtURL:destinationURL error:nil];
 }
 BOOL success = [fileManager copyItemAtURL:location
                                    toURL:destinationURL
                                    error:&error];
 if (success)
  {
    [[NSOperationQueue mainQueue] addOperationWithBlock:^{
        NSLog(@"Download completed!");
        NSLog(@"destination file name : %@!",destinationFilename);
        NSLog(@"Part id of file name : %@!",self.part_id);
        [self performSelectorOnMainThread:@selector(updateProgress:) withObject:[NSString stringWithFormat:@"1.0"] waitUntilDone:NO];

        [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;

        NSString *filenameValue=[NSString stringWithFormat:@"%@",destinationFilename];
        NSString *hideExtension=[filenameValue substringToIndex:filenameValue.length-4];
        NSLog(@"filenameValue == %@", filenameValue);

        [self DBUpdateVideoURLStatus:self.part_id andFileName:filenameValue];
        [self DBInsertDownloads:self.part_id andFileName:filenameValue];

        UIAlertView *alert=[[UIAlertView alloc]initWithTitle:NSLocalizedString(@"Success", @"Success message") message:[NSString localizedStringWithFormat:@"%@ downloaded successfully!",hideExtension] delegate:self cancelButtonTitle:NSLocalizedString(@"Ok", @"Ok action") otherButtonTitles:nil];
        alert.tag = 1;
        [alert show];
        [alert release];
        [self.session finishTasksAndInvalidate];
    }];
 }
 else
  {
    NSLog(@"Unable to copy temp file. Error: %@", [error localizedDescription]);
  }
}

-(void)updateProgress:(id)progress
{
  float currentProgress = [progress floatValue];
  [self.downloadProgress setProgress:currentProgress animated:YES];
  [self.downloadProgress setNeedsDisplay];
  [self.tblview reloadData];
}

Answer 1

你说：

当我尝试下载并删除它并再次下载时尝试在已失效的会话中创建任务 *** 由于未捕获的异常“NSGenericException”而终止应用程序，原因：“在具有已作废'

这是因为您正在调用finishTasksAndInvalidate，它告诉NSURLSession 它不仅应该完成所有队列任务，还应该使会话无效并且不允许更多任务。但是还有另一个任务要运行，但是您使会话无效。

底线，随意取消任务，但如果您要为同一个会话对象启动更多任务，请不要使会话对象无效。

Answer 2

我注意到一个错误：

mainQueue 在主线程上处理，因此您不应从在主队列上执行的块中调用 performSelectorOnMainThread。

在下载任务结束时到达主线程的标准模式是将异步调度到主队列，而不是像您所做的那样向主队列添加操作。

Answer 3

您能否尝试更改以下代码并告诉我们结果如何：

-(void)updateProgress:(id)progress
{
    dispatch_async(dispatch_get_main_queue(), ^{

        float currentProgress = [progress floatValue];
        [self.downloadProgress setProgress:currentProgress animated:YES];
        [self.downloadProgress setNeedsDisplay];

    });
    [self.tblview reloadData];
}