[英]C# return from async task not working
我正在使用HttpClient進行異步http調用。 該調用在異步任務內進行。 調用成功,並且從Http調用中得到響應。 但是,當我嘗試從任務返回響應時,即使返回后有一個斷點在等待,也沒有任何反應。
public void ExecuteTask(Foundation.Security.SecurityToken token, Order order)
{
ExecuteTaskAsync(token, order).Wait();
}
public async Task ExecuteTaskAsync(Foundation.Security.SecurityToken token, Order order)
{
if (order != null)
{
log.Info("Starting export of order " + order.ID.ToString());
bool success = await ExportOrder(order, token);
if (!success)
{
log.Error("Failed to export order with ID " + order.ID.ToString());
}
}
}
private async Task<bool> ExportOrder(Order order, Foundation.Security.SecurityToken token)
{
try
{
ResponseObject response = await webService.SendOrder(new SenderInformation(token), new ReceiverInformation(order, token));
if (response.Success && response.Status.Equals("201", StringComparison.OrdinalIgnoreCase))
{
log.Info(String.Format("Order ({0}) was successfully exported"), order.ExternalOrderID);
return true;
}
return false;
}
catch (Exception e)
{
log.Error(String.Format("Exception occured while exporting order ({0})", order.ID), e);
return false;
}
}
以下是執行實際http調用的代碼。 我將最后一條功能行標記為“代碼成功到達此行。此后一切都沒有”
public Task<ResponseObject> SendOrder(SenderInformation sender, ReceiverInformation receiver)
{
OrderRequest request = new OrderRequest(sender, receiver);
return ExecuteRequest<OrderRequest, ResponseObject>(request);
}
private async Task<ResponseType> ExecuteRequest<RequestType, ResponseType> (RequestType request)
where RequestType : RequestObject
where ResponseType : class, ResponseObject, new()
{
try
{
using (var client = new HttpClient())
{
string xml = SerializeRequest(request);
HttpContent content = new StringContent(xml);
content.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("text/xml");
string requestUrl = "URL";
HttpResponseMessage response = await client.PostAsync(requestUrl, content).ConfigureAwait(false);
// Parse response
if (response.IsSuccessStatusCode)
{
Stream responseStream = await response.Content.ReadAsStreamAsync();
ResponseType responseObject = DeserializeResponse<ResponseType>(responseStream);
if (responseObject != null)
{
responseObject.Success = true;
return responseObject; //The code successfully reach this line. After this nothing happens
}
else
{
log.Error("Response could not be deserialized");
}
}
else
{
log.Error("Error during request, got status code " + response.StatusCode);
}
}
}
catch (Exception e)
{
log.Error("Something went wrong!", e);
}
return new ResponseType() { Success = false };
}
問題在這條線上:
ExecuteTaskAsync(token, order).Wait();
這將導致死鎖:由於UI線程被阻塞,因此被調用方法中的await
無法恢復。
使用異步代碼時,必須始終使用它。 永遠不要同步等待異步任務完成。
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