我有 2 个项目，使用 2 种不同的语言。 Objective-c 项目和 swift 项目从 url 下载文件。

问题是在 objective-c 中文件下载速度比在 swift 中快。为什么会这样？如何解决？

我的快速代码:

override func viewDidLoad() {
    super.viewDidLoad()

    let backgroundSessionConfiguration = URLSessionConfiguration.background(withIdentifier: "backgroundSession")
    backgroundSession = Foundation.URLSession(configuration: backgroundSessionConfiguration, delegate: self, delegateQueue: OperationQueue.main)
}

override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {



    if indexPath.row > 0 { print(indexPath.row)

        let path = NSSearchPathForDirectoriesInDomains(FileManager.SearchPathDirectory.documentDirectory, FileManager.SearchPathDomainMask.userDomainMask, true)
        print(path)
        let documentDirectoryPath:String = path[0]
        let fileManager = FileManager()
        let destinationURLForFile = URL(fileURLWithPath: documentDirectoryPath.appendingFormat("/file\(indexPath.row).mp3"))


        if fileManager.fileExists(atPath: destinationURLForFile.path){

            self.performSegue(withIdentifier: "detailSegue", sender: self)
            print(indexPath.row)
        }else{

            index = indexPath.row

            let url = URL(string: "link\(indexPath.row).mp3")!
            downloadTask = backgroundSession.downloadTask(with: url)
            downloadTask.resume()


            circularProgressView = FFCircularProgressView(frame: CGRect(x: CGFloat(0), y: CGFloat(0), width: CGFloat(24), height: CGFloat(24)))
            tableView.cellForRow(at: indexPath)?.accessoryView = self.circularProgressView
            self.view.addSubview(circularProgressView)
            circularProgressView.startSpinProgressBackgroundLayer()

        }
    }   
}

//MARK: URLSessionDownloadDelegate
func urlSession(_ session: URLSession,
                downloadTask: URLSessionDownloadTask,
                didFinishDownloadingTo location: URL){

    let path = NSSearchPathForDirectoriesInDomains(FileManager.SearchPathDirectory.documentDirectory, FileManager.SearchPathDomainMask.userDomainMask, true)
    let documentDirectoryPath:String = path[0]
    let fileManager = FileManager()
    let destinationURLForFile = URL(fileURLWithPath: documentDirectoryPath.appendingFormat("/file\(index).mp3"))

    do {
        try fileManager.moveItem(at: location, to: destinationURLForFile)
        }catch{
            print("An error occurred while moving file to destination url")
        }
}
func urlSession(_ session: URLSession,
                downloadTask: URLSessionDownloadTask,
                didWriteData bytesWritten: Int64,
                totalBytesWritten: Int64,
                totalBytesExpectedToWrite: Int64){

    progress1 = Int(Float(totalBytesWritten))
    total1 = Int(Float(totalBytesExpectedToWrite))
    let percentage = String(format: "%.f%%", ((self.progress1 / self.total1) * 100))
    (print(String(format: percentage, "%.f%%")))
    DispatchQueue.main.async(execute: {() -> Void in
        self.circularProgressView.progress = (CGFloat(self.progress1) / CGFloat(self.total1))
        self.circularProgressView.stopSpinProgressBackgroundLayer()
    })
}

//MARK: URLSessionTaskDelegate
func urlSession(_ session: URLSession,
                task: URLSessionTask,
                didCompleteWithError error: Error?){
    downloadTask = nil
    if (error != nil) {
        print(error!.localizedDescription)
    }else{
        print("The task finished transferring data successfully")
    }
}

我的 Objective-C 代码:

- (void)viewDidLoad
{
[super viewDidLoad];

_session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration] delegate:self delegateQueue:[NSOperationQueue mainQueue]];
}


- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{


if (indexPath.row == 1) {
        NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
        NSString *documentsDirectory = [paths objectAtIndex:0];
        NSString *filePath = [documentsDirectory stringByAppendingPathComponent:@"file2.mp3"];
        BOOL fileExists = [[NSFileManager defaultManager] fileExistsAtPath:filePath isDirectory:false];
        if (!fileExists) {

            UIAlertController * alert = [UIAlertController
                                         alertControllerWithTitle:@""
                                         message:@""
                                         preferredStyle:UIAlertControllerStyleActionSheet];
            UIAlertAction* actionAdd = [UIAlertAction
                                        actionWithTitle:@""
                                        style:UIAlertActionStyleDefault
                                        handler:^(UIAlertAction * action)
                                        {
                                            [alert dismissViewControllerAnimated:YES completion:nil];

                                            _url1 =[NSURL URLWithString:@"link/file2.mp3"];
                                            _downloadTask1 = [_session downloadTaskWithURL:_url1];
                                            [_downloadTask1 resume];

                                            self.circularPV1 = [[FFCircularProgressView alloc] initWithFrame:CGRectMake(0, 0, 24, 24)];

                                            [tableView cellForRowAtIndexPath:indexPath].accessoryView = self.circularPV1;
                                            [self.view addSubview:_circularPV1];

                                            [_circularPV1 startSpinProgressBackgroundLayer];

                                        }];

            UIAlertAction* actionCancel = [UIAlertAction
                                           actionWithTitle:@""
                                           style:UIAlertActionStyleCancel
                                           handler:^(UIAlertAction * action)
                                           {
                                               [alert dismissViewControllerAnimated:YES completion:nil];
                                           }];
            [alert addAction:actionAdd];
            [alert addAction :actionCancel];
            alert.popoverPresentationController.sourceView = self.view;
            alert.popoverPresentationController.sourceRect = CGRectMake(self.view.bounds.size.width / 3.4, self.view.bounds.size.height / 4.0, 1.0, 1.0);
            [self presentViewController:alert animated:YES completion:nil];
        }
        if (fileExists) {
            [self performSegueWithIdentifier: @"detailSegue" sender: self];
        }
    }
}

- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location
{

if (downloadTask == _downloadTask1) {

    _paths1 = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    _documentsDirectory1 = [_paths1 objectAtIndex:0];
    NSFileManager *fileManager = [NSFileManager defaultManager];
    NSURL *newLocation = [NSURL URLWithString:[NSString stringWithFormat:@"file://%@/file2.mp3", _documentsDirectory1]];
    NSError *error;
    [fileManager copyItemAtURL:location toURL:newLocation error:&error];
}
}

- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten  totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite;
{
if( downloadTask == _downloadTask1){
    self.progress1 = (float) totalBytesWritten;
    self.total1 =  (float) totalBytesExpectedToWrite;
    NSString *percentage = [NSString stringWithFormat:@"%.f%%", ((_progress1 / _total1) * 100)];
    (NSLog (percentage, @"%.f%%"));
    dispatch_async(dispatch_get_main_queue(), ^{
        [_circularPV1 setProgress:(_progress1 / _total1)];
        [_circularPV1 stopSpinProgressBackgroundLayer];
    });
}
}

最佳答案

您的 swift 代码正在使用后台 URL session 。操作系统给予这些下载较低的优先级。

如果您不需要使用后台 session ，您可以在创建 session 时模仿 Objective C 代码:

session = URLSession(configuration:URLSessionConfiguration.default delegate:self delegateQueue:OperationQueue.main)

关于ios - 使用 swift 和 objective-c 下载文件，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/42886955/