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，请确保该页面被标记为<％@ Page Async =“ true”％>。此异常也可能表示尝试调用“异步无效”方法，ASP.NET请求处理通常不支持该方法。相反，异步方法应返回一个Task，而调用者应等待它。

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()被声明为async方法，因此调用该方法的控制器还必须具有async返回类型的Task<ActionResult>修饰符，而不是常规的ActionResult，因为async方法无法与异常消息中提到的同步处理程序一起正常使用：

[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);
}

但是，我建议您避免使用async void方法定义，但是可以看到原因here。我建议使用void以外的其他返回类型，例如string，如果您想返回一个字符串并像这样分配它：

var result = await MakeRequest(model.ProductSN);