asp.net-mvc - TempData 始终为空

Question

我想使用 TempData 来存储 Post 和后续重定向之间的消息，但 TempData 始终为空。

我有 BaseContoller 提供一些用于传递 TempData 的基础设施。简化的代码如下所示:

public abstract class BaseController : Controller
{
  public const string AuditMessagesKey = "AuditMessages";

  private List<InformationMessage> _informationMessages = new List<InformationMessage>();

  protected BaseController()
  {
    // I also tried this in overriden Initialize
    ViewData[AuditMessagesKey] = GetAuditMessages();
  }

  protected void AddAuditMessage(InformationMessage message)
  {
    if (message == null)
      return;

     _informationMessages.Add(message);
  }

  protected override void OnResultExecuting(ResultExecutingContext filterContext)
  {
    base.OnResultExecuting(filterContext);

    if (filterContext.Result is RedirectToRouteResult)
    {
      // I see that messages are stored into TempData
      TempData[AuditMessagesKey] = _informationMessages;
      // This also doesn't help
      // TempData.Keep(AuditMessagesKey);
    }
  }

  private ICollection<InformationMessage> GetAuditMessages()
  {
    // TempData are always empty here
    var messages = TempData[AuditMessagesKey] as List<InformationMessage>;

    if (messages == null)
    {
      messages = new List<InformationMessage>();
    }

    return messages;
  }
}

操作方法如下:

  [HttpPost]
  public ActionResult CancelEdit(RequestSaveModel model)
  {
    AddAuditMessage(new InformationMessage
      {
        Message = String.Format(Messages.RequestEditationCanceled, model.Title),
        Severity = MessageSeverity.Information
      });

    return RedirectToAction("Detail", new { Id = model.Id});
  }

应用程序已在 VS Development Web 服务器上进行测试。没有 Ajax 调用，并且我从母版页中删除了所有 Html.RenderAction 调用。我可以看到，在 GetAuditedMessages 中每个请求仅访问 TempData 一次，并且在 OnResultExecuting 中仅存储一次。没有任何内容会覆盖数据。允许 session 状态。

代码稍微简化了一些。我们还使用防伪 token 、自定义过滤器进行授权和操作选择，但它不应影响 TempData 行为。

我不明白。我之前在测试应用程序中使用过 TempData，效果很好。

Answer 1

我在代码中看到的问题是，您试图在 Controller 的构造函数中从 TempData 检索数据 - 这是在数据可用之前。

将对 GetAuditMessages() 的调用移至 OnActionExecuting 方法中，这样就可以访问该方法了。

public abstract class BaseController : Controller
{
  public const string AuditMessagesKey = "AuditMessages";

  private List<InformationMessage> _informationMessages = new List<InformationMessage>();

  protected BaseController()
  {
    // TempData is not available yet
  }

  protected override void OnActionExecuting(ActionExecutingContext filterContext)
  {
      ViewData[AuditMessagesKey] = GetAuditMessages();

      base.OnActionExecuting(filterContext);
  }

  protected void AddAuditMessage(InformationMessage message)
  {
    if (message == null)
      return;

     _informationMessages.Add(message);
  }

  protected override void OnResultExecuting(ResultExecutingContext filterContext)
  {
    base.OnResultExecuting(filterContext);

    if (filterContext.Result is RedirectToRouteResult)
    {
      // I see that messages are stored into TempData
      TempData[AuditMessagesKey] = _informationMessages;
      // This also doesn't help
      // TempData.Keep(AuditMessagesKey);
    }
  }

  private ICollection<InformationMessage> GetAuditMessages()
  {
    var messages = TempData[AuditMessagesKey] as List<InformationMessage>;

    if (messages == null)
    {
      messages = new List<InformationMessage>();
    }

    return messages;
  }
}