出错时重试异步文件上传

Question

我正在尝试在 WPF 应用程序中上传文件。如果服务器响应，则一切正常，但应用程序将在具有“不安全”互联网连接的环境中使用。因此，如果第一次尝试失败，我想在短暂休息后重试上传。

我用 async/await 尝试了一些事情，最终得到了以下代码。如果服务器正在运行，则一切正常，但如果没有，程序将在 while 循环的第二次迭代中失败并出现 ObjectDisposeException。

有任何想法吗？

private void UploadButton_Click(object sender, RoutedEventArgs e)
{
    // build content to send
    content = new MultipartFormDataContent();
    var filestream = new FileStream(filePath, FileMode.Open);
    var fileName = System.IO.Path.GetFileName(filePath);
    content.Add(new StreamContent(filestream), "file", fileName);
    content.Add(new StringContent(terminal_id.ToString()), "terminal_id");

    UploadTask(content);
    /*var task_a = new Task(() => UploadTask(content));
    task_a.Start();*/
}

private async void UploadTask(HttpContent content)
{
    bool success = false;
    int counter = 0;

    while (counter < 3 && !success)
    {
        Debug.WriteLine("starting upload");
        success = await UploadFileAsync(content);
        Debug.WriteLine("finished upload. result " + success.ToString());
        //if (!success) System.Threading.Thread.Sleep(5000);
        counter++;
    }
}

private async Task<bool> UploadFileAsync(HttpContent content)
{
    var message = new HttpRequestMessage();
    message.Method = HttpMethod.Post;
    message.Content = content;
    message.RequestUri = new Uri(target_url);

    using (HttpClient client = new HttpClient())
    {
        try
        {
            HttpResponseMessage res = await client.SendAsync(message);
            if (res.IsSuccessStatusCode) return true;
        }
        catch (HttpRequestException hre)
        {
            Debug.WriteLine(hre.ToString());
        }
        return false;
    }
}

Answer 1

将内容的创建移至 UploadFileAsync() 后，它就可以工作了。结果：

Task<bool> newTask;

private void UploadButton_Click(object sender, RoutedEventArgs e)
{
    newTask = UploadTask();
}

private async Task<bool> UploadTask()
{
    bool success = false;
    int counter = 0;

    while (counter < 3 && !success)
    {
        Debug.WriteLine("starting upload");
        success = await UploadFileAsync();
        Debug.WriteLine("finished upload. result " + success.ToString());
        if (!success) System.Threading.Thread.Sleep(5000);
        counter++;
    }
    return success;
}

private async Task<bool> UploadFileAsync()
{
    MultipartFormDataContent content = new MultipartFormDataContent();
    var filestream = new FileStream(filePath, FileMode.Open);
    var fileName = System.IO.Path.GetFileName(filePath);
    content.Add(new StreamContent(filestream), "file", fileName);
    content.Add(new StringContent(terminal_id.ToString()), "terminal_id");

    var message = new HttpRequestMessage();
    message.Method = HttpMethod.Post;
    message.Content = content;
    message.RequestUri = new Uri(target_url);

    using (HttpClient client = new HttpClient())
    {
        try
        {
            HttpResponseMessage res = await client.SendAsync(message);
            if (res.IsSuccessStatusCode) return true;
        }
        catch (HttpRequestException hre)
        {
            Debug.WriteLine(hre.ToString());
        }
        return false;
    }
}