如何在 ASP.NET MVC 控制器中调用异步方法？

Question

我试图在 ASP.NET MVC 控制器中调用 async 方法，但出现异常：

此时无法启动异步操作。异步操作只能在异步处理程序或模块内或在页面生命周期中的某些事件期间启动。如果在执行页面时发生此异常，请确保将页面标记为 。此异常还可能表示尝试调用“async void”方法，在 ASP.NET 请求处理中通常不支持该方法。相反，异步方法应该返回一个 Task，调用者应该等待它。

我的代码：

控制器：

[HttpGet]
public ActionResult OfferDetailsPage(string id)
{
    // string userid = ClaimsPrincipal.Current.FindFirst(ClaimTypes.Name).Value.ToString();
    // var u_role = db.UserDetails.Where(x => x.ADID == userid).FirstOrDefault();
    // if (u_role == null)
    // {
    //    return RedirectToAction("Unauthorize", "Account");
    // }
    // else if (u_role.TypeOfUser.ToLower() != "validator")
    // {
    //    return RedirectToAction("Unauthorize", "Account");
    // }

    ProductOfferDetails model = new ProductOfferDetails();

    AssignedOffersImplementation offerdetail_ = new AssignedOffersImplementation();

    DataSet dstProductlist = offerdetail_.GetOfferSubmittedById(id);

    if(dstProductlist.Tables[0].Rows[0]["status"].ToString()!="Active")
    {
        return Content("Offer moved from here..");
    }

    model.Offer_UOID = dstProductlist.Tables[0].Rows[0]["Offer_UOID"].ToString();
    model.OfferId = dstProductlist.Tables[0].Rows[0]["Offer_Id"].ToString();
    model.ProductURL = dstProductlist.Tables[0].Rows[0]["Offer_pgURL"].ToString();
    // string ProductURL = dstProductlist.Tables[0].Rows[0]["Offer_pgURL"].ToString();
    model.DatePublication = Convert.ToDateTime(dstProductlist.Tables[0].Rows[0]["Date_Publication"].ToString());
    // model.SoldDate = Convert.ToDateTime(dstProductlist.Tables[0].Rows[0]["Date_Sold"].ToString());
    model.OfferStatus = dstProductlist.Tables[0].Rows[0]["OfferStatus"].ToString();
    model.SellerComments = dstProductlist.Tables[0].Rows[0]["Seller_Comments"].ToString();
    model.Product_Title = dstProductlist.Tables[0].Rows[0]["Product_Title"].ToString();
    model.Offer_Sk = dstProductlist.Tables[0].Rows[0]["Offer_Sk"].ToString();
    model.ProductSN = dstProductlist.Tables[0].Rows[0]["ProductSN"].ToString();
    // model.ImageURL = dstProductlist.Tables[0].Rows[0]["Image_url"].ToString();
    model.SNSticker = dstProductlist.Tables[0].Rows[0]["SN_sticker"].ToString();
    model.CH_Fashion_Intranet = dstProductlist.Tables[0].Rows[0]["CH_Fashion_Intranet"].ToString();
    // model.SNTag = dstProductlist.Tables[0].Rows[0]["SN_Tag"].ToString();
    model.SNCard = dstProductlist.Tables[0].Rows[0]["SN_Card"].ToString();
    // model.ValidatorComments = dstProductlist.Tables[0].Rows[0]["Validator_Comments"].ToString();
    // model.IntialSN = dstProductlist.Tables[0].Rows[0]["Initial_SN"].ToString();
    model.SNComments = dstProductlist.Tables[0].Rows[0]["SN_comments"].ToString();
    model.SNCertificate = dstProductlist.Tables[0].Rows[0]["SN_Certificate"].ToString();
    // model.DateIdentification = dstProductlist.Tables[0].Rows[0]["DateIdentification"].ToString();
    model.Offer_UOID = dstProductlist.Tables[0].Rows[0]["Offer_UOID"].ToString();
    model.OfferId = dstProductlist.Tables[0].Rows[0]["Offer_Id"].ToString();
    model.ProductURL = dstProductlist.Tables[0].Rows[0]["Offer_pgURL"].ToString();
    string ProductURL = dstProductlist.Tables[0].Rows[0]["Offer_pgURL"].ToString();
    model.DatePublication = Convert.ToDateTime(dstProductlist.Tables[0].Rows[0]["Date_Publication"].ToString());
    model.SoldDate = (dstProductlist.Tables[0].Rows[0]["Date_Sold"].ToString());
    model.OfferStatus = dstProductlist.Tables[0].Rows[0]["OfferStatus"].ToString();
    // model.SellerComments = dstProductlist.Tables[0].Rows[0]["Seller_Comments"].ToString();
    model.Product_Title = dstProductlist.Tables[0].Rows[0]["Product_Title"].ToString();
    model.Offer_Sk = dstProductlist.Tables[0].Rows[0]["Offer_Sk"].ToString();

    // if (dstProductlist.Tables[0].Rows[0]["SNEnteredStatus"ToString() == "True")
    // {
    //    return Content("Offer Already Submitted");
    // };
    // model.ProductSN = dstProductlist.Tables[0].Rows[0]["ProductSN"].ToString();
    // model.ImageURL = dstProductlist.Tables[0].Rows[0]["Image_url"].ToString();
    // model.SNSticker = dstProductlist.Tables[0].Rows[0]["SN_sticker"].ToString();
    // model.CH_Fashion_Intranet = dstProductlist.Tables[0].Rows[0]["CH_Fashion_Intranet"].ToString();
    // model.SNTag = dstProductlist.Tables[0].Rows[0]["SN_Tag"].ToString();
    // model.SNCard= dstProductlist.Tables[0].Rows[0]["SN_Card"].ToString();
    // model.ValidatorComments = dstProductlist.Tables[0].Rows[0]["Validator_Comments"].ToString();
    // model.IntialSN = dstProductlist.Tables[0].Rows[0]["Initial_SN"].ToString();
    // model.SNComments = dstProductlist.Tables[0].Rows[0]["SN_comments"].ToString();
    // model.SNCertificate = dstProductlist.Tables[0].Rows[0]["SN_Certificate"].ToString();

    DataSet dstBlobImages = offerdetail_.BlobImages(model.Offer_Sk);
    IEnumerable<Models.BlobImages> _blobs = DataTableExtentions.ToList<Models.BlobImages>(dstBlobImages.Tables[0]);
    model.blobs = _blobs;

    IEnumerable<ProductOfferDetails> _Productimageslist = DataTableExtentions.ToList<ProductOfferDetails>(dstProductlist.Tables[0]);

    TempData["SN_Tag"] = model.SNTag;
    TempData["SN"] = model.ProductSN;
    TempData["CH_Fashion_Intranet"] = model.CH_Fashion_Intranet;
    TempData["SN_Certificate"] = model.SNCertificate;
    TempData["SN_Sticker"] = model.SNSticker;
    TempData["SN_Comments"] = model.SNComments;
    TempData["SN_Card"] = model.SNCard;

    string itemcode = string.Empty;
    string stylecode = string.Empty;

    GetORLIData(model.ProductSN);
    MakeRequest(model.ProductSN);

    if (Session["itemcode"] != null)
    {
        itemcode = Session["itemcode"].ToString();
        stylecode = Session["stylecode"].ToString();

        Session.Remove("itemcode");
        Session.Remove("stylecode");
    }

    // var photo = GetPhoto(model.ProductSN);
    ViewBag.itemcode = itemcode;
    ViewBag.stylecode = stylecode;

    return View(model);
}   

异步方法：

    public  static async void MakeRequest(string serial)
    {
        var client = new HttpClient();
        var queryString = HttpUtility.ParseQueryString(string.Empty);

        // Request headers
        client.DefaultRequestHeaders.Add("Authorization", "Basic Y2NAdGVzdC5jaGFuZWwtY29ycC5jb206cGFzc3dvcmQ=");
        client.DefaultRequestHeaders.Add("X-API-Key", "computer-vision");
        client.DefaultRequestHeaders.Add("lang", "en");
        client.DefaultRequestHeaders.Add("Ocp-Apim-Subscription-Key", "5d8c7294fed64d009cadcaea2fc2dff0");

        string serialNumber = "18845681";

        string uri = string.Format("https://int-apim.lpl-cloud.com/int/fshcatalog/serial/products/v1/fsh/serial/{0}?" + queryString, serialNumber);



        var response = await client.GetAsync(uri);

        string EmpResponse = string.Empty;

        if (response.IsSuccessStatusCode)
        {
            EmpResponse = response.Content.ReadAsStringAsync().Result;
        }


        var details = JObject.Parse(EmpResponse);

        string photo = details["photo"].ToString();
        string libelleColorisCommercial = details["libelleColorisCommercial"].ToString();
        string codeArticle = details["codeArticle"].ToString();

        string codeColorCommercial = details["codeColorCommercial"].ToString();


        string Param = codeArticle + codeColorCommercial;

        string uri2 = string.Format("https://int-apim.lpl-cloud.com/int/fshcatalog/product/products/v1/fsh/products/{0}?" + queryString, Param);
        var response2 = await client.GetAsync(uri2);
        string dimension = string.Empty;
        if (response2.IsSuccessStatusCode)
        {
            dimension = response2.Content.ReadAsStringAsync().Result;
        }
        var dim = JObject.Parse(dimension);

        string dimensioncode = dim["dimensionsCode"].ToString();

        //Session["photo"] = photo;
        //Session["libelleColorisCommercial"] = libelleColorisCommercial;
        //Session["dimensioncode"] = dimensioncode;

    }

请给我建议在 ASP.NET MVC 控制器中调用异步方法

Answer 1

由于MakeRequest() 声明为async 方法，调用该方法的控制器也必须具有async 修饰符和Task<ActionResult> 返回类型，而不是正常的ActionResult，因为async 方法在同步时不能正常工作异常消息中提到的处理程序：

[HttpGet]
public async Task<ActionResult> OfferDetailsPage(string id)
{
    // other stuff

    // calling async method, this must be await-ed
    await MakeRequest(model.ProductSN);

    // other stuff

    return View(model);
}

不过我建议你避免async void的方法定义，你可以看看here的原因。我建议使用 void 以外的其他返回类型，例如string 如果你想返回一个字符串并像这样分配它：

var result = await MakeRequest(model.ProductSN);