Question

我已尝试（并且失败）从WPF应用程序进行异步Web服务调用。

当我按下GUI上的“发送”按钮时，我在我的代码中实现了BackgroundWorker，这应该可以完成工作。它做了它应该做的事情，某些时候，但最终它实际上并不是异步运行。

当您按下我的GUI中的按钮时，会触发以下代码：

private void btnSend_Click(object sender, RoutedEventArgs e)
{
    sQuantity = boxQuantity.Text;
    progressBar.Maximum = double.Parse(sQuantity);
    worker.RunWorkerAsync();
}

sQuantity只是一个包含数字的方框。它将确定您一次向Web服务发送的请求数。

progressBar就是您所期望的：进度条。

worker.RunWorkerAsync()是我称之为DoWork方法的地方。它看起来像这样：

void worker_DoWork(object sender, DoWorkEventArgs e)
{
    EnableButton(false);
    List<LoanRequestNoCreditScoreDTO> dtoList = GetData();
    foreach (LoanRequestNoCreditScoreDTO dto in dtoList)
    {
        using (LoanBrokerWS.LoanBrokerWSClient client = new LoanBrokerWS.LoanBrokerWSClient())
        {
            try
            {
                Task<LoanQuoteDTO> lq = RequestQuote(dto, client);
                LoanQuoteDTO response = lq.Result;
                lq.Dispose();
                String responseMsg = response.SSN + "\n" + response.interestRate + "\n" + response.BankName + "\n------\n";
                AppendText(responseMsg);
                worker_ProgressChanged();
            }
            catch (Exception ex)
            {
                AppendText(ex.Message + "\n" + ex.InnerException.Message + "\n");
                worker_ProgressChanged();
            }
        }
    }
    EnableButton(true);
}

最终，这是我搞砸的地方。我希望应用程序发送与用户指定的请求一样多的请求。所以，如果我写了10个数量，我会发送10个请求。 RequestQuote()方法调用以下代码：

private async Task<LoanQuoteDTO> RequestQuote(LoanRequestNoCreditScoreDTO dto, LoanBrokerWS.LoanBrokerWSClient client)
{
    LoanQuoteDTO response = await client.GetLoanQuoteAsync(dto.SSN, dto.LoanAmount, dto.LoanDuration);
    return response;
}

如何让DoWork方法实际发送请求异步？

Answer 1

代码as-is与UI线程是异步的;你在问什么并发。任何类型的复杂I / O工作最好使用async / await完成，因此我要抛弃后台工作人员并直接使用async。

首先，按钮处理程序将处理自己的启用/禁用并执行主下载：

private async void btnSend_Click(object sender, RoutedEventArgs e)
{
  var quantity = int.Parse(boxQuantity.Text);
  btnSend.Enabled = false;
  await DownloadAsync(quantity);
  btnSend.Enabled = true;
}

主下载将创建速率限制SemaphoreSlim（用于限制并发异步操作的常用类型），并等待所有单个下载完成：

private async Task DownloadAsync(int quantity)
{
  var semaphore = new SemaphoreSlim(quantity);
  var tasks = GetData().Select(dto => DownloadAsync(dto, semaphore));
  await Task.WhenAll(tasks);
}

个人下载将首先限制自己，然后进行实际下载：

private async Task DownloadAsync(LoanRequestNoCreditScoreDTO dto, SemaphoreSlim semaphore)
{
  await semaphore.WaitAsync();
  try
  {
    using (LoanBrokerWS.LoanBrokerWSClient client = new LoanBrokerWS.LoanBrokerWSClient())
    {
      var response = await RequestQuoteAsync(dto, client);
    }        
  }
  finally
  {
    semaphore.Release();
  }
}

为了执行进度报告，我建议使用针对该模式的类型（IProgress<T> / Progress<T>）。首先，您可以在进度报告中确定所需的数据;在这种情况下，它可能只是一个字符串。然后，您创建进度处理程序：

private async void btnSend_Click(object sender, RoutedEventArgs e)
{
  var quantity = int.Parse(boxQuantity.Text);
  var progress = new Progress<string>(update =>
  {
    AppendText(update);
    progressBar.Value = progressBar.Value + 1;
  });
  progressBar.Maximum = ...; // not "quantity"
  btnSend.Enabled = false;
  await DownloadAsync(quantity, progress);
  btnSend.Enabled = true;
}

（请注意原始代码中的progressBar.Maximum = double.Parse(sQuantity);错误;您应将其设置为总下载次数。）

然后传递IProgress<string>：

private async Task DownloadAsync(int quantity, IProgress<string> progress)
{
  var semaphore = new SemaphoreSlim(quantity);
  var tasks = GetData().Select(dto => DownloadAsync(dto, semaphore, progress));
  await Task.WhenAll(tasks);
}

当您有进度报告时，您可以使用该实例：

private async Task DownloadAsync(LoanRequestNoCreditScoreDTO dto, SemaphoreSlim semaphore, IProgress<string> progress)
{
  await semaphore.WaitAsync();
  try
  {
    using (LoanBrokerWS.LoanBrokerWSClient client = new LoanBrokerWS.LoanBrokerWSClient())
    {
      var response = await RequestQuoteAsync(dto, client);
      progress.Report(response.SSN + "\n" + response.interestRate + "\n" + response.BankName + "\n------\n");
    }
  }
  catch (Exception ex)
  {
    progress.Report(ex.Message + "\n" + ex.InnerException.Message + "\n");
  }
  finally
  {
    semaphore.Release();
  }
}

Answer 2

如果您使用await关键字调用RequestQuote，那么在每次调用中它都会等待响应，而您无法再创建另一个。所以，只需使用您的代理＆＃34; 已完成的事件处理程序＆＃34;对于您的异步方法并调用RequestQuote方法，并在事件处理程序中提供响应。

来自WPF的异步Web服务请求

2 个答案: