ios - 如何在导航 View Controller 时获取当前正在运行的 NSURLSession 后台 session ？

Question

我正在开发一个 iOS 应用程序，用于从服务器下载文件 (<10MB)。我使用 NSURLSession 和 NSURLSessionDownloadTask 进行下载。

我的问题是，下载 View Controller 不是 rootViewController。当我返回到 Root View Controller 时，我可以看到下载进度仍然有效(来自 NSLog)。但是当我再次下载 View Controller 时，我看不到我的标签根据进度更新了。在这种情况下，我如何才能获取当前正在运行的 NSURLSession 后台 session 来更新我的状态标签？或者其他解决方案？

//Start downloading
-(void)startDownload: (NSString *)url{
    NSString *sessionId = MY_SESSION_ID;
    NSURLSessionConfiguration *sessionConfiguration = [NSURLSessionConfiguration backgroundSessionConfiguration:sessionId];
    sessionConfiguration.HTTPMaximumConnectionsPerHost = 1;
    self.session = [NSURLSession sessionWithConfiguration:sessionConfiguration
                                                    delegate:self
                                            delegateQueue:nil];
    self.downloadTask = [self.session downloadTaskWithURL:[NSURL URLWithString:url]];
    [self.downloadTask resume];
}

//Delegate
-(void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite{

    if (totalBytesExpectedToWrite == NSURLSessionTransferSizeUnknown) {
        NSLog(@"Unknown transfer size");
    }
    else{
        [[NSOperationQueue mainQueue] addOperationWithBlock:^{
            NSInteger percentage = (double)totalBytesWritten * 100 / (double)totalBytesExpectedToWrite;
            self.percentageLabel.text = [NSString stringWithFormat:@"Downloading (%ld%%)", (long)percentage];
            NSLog(@"Progress: %ld", (long)percentage);
        }];
    }
}

Answer 1

这就是我在我的代码中所做的并且它起作用了:

[self performSelectorOnMainThread:@selector(setuploadStatus:) withObject:[NSString stringWithFormat:@"Upload %ld%%", (long)percentage] waitUntilDone:NO];

-(void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didSendBodyData:(int64_t)bytesSent totalBytesSent:(int64_t)totalBytesSent totalBytesExpectedToSend:(int64_t)totalBytesExpectedToSend {

    NSInteger percentage = (double)totalBytesSent * 100 / (double)totalBytesExpectedToSend;

    **[self performSelectorOnMainThread:@selector(setuploadStatus:) withObject:[NSString stringWithFormat:@"Upload %ld%%", (long)percentage] waitUntilDone:NO];**

    NSLog(@"Upload %ld%% ",(long)percentage);

}

-(void) setuploadStatus : (NSString *) setStat  {

    [_notifyTextLabel setText:setStat];

}