Question

我试图创建一个基本的ASP.NET应用程序，使用名为FatSecret Sharp的包装器调用Fatsecret API，但是当我尝试从我的JS调用服务器端方法时出现此错误脚本，我想确定如何成功使用此包装器来创建Web应用程序。

您会注意到来自包装器的API调用明确提到它是＆＃34;同步＆＃34;，所以我假设发生错误的是什么，我只是不知道＆＃34; ＃39;不知道为什么，或者如何使用Web应用程序成功使用该调用。

这是我的代码：

的Javascript

var jsonData;

function search() {
    var element = document.getElementById("searchField")
    var searchTerm = element.value;

    callAJAX("FoodSearchExample", searchTerm);
}

function callAJAX(requestMethod, term) {
    var pageMethod = "default.aspx/" + requestMethod;

    $.ajax({
    url: pageMethod,
    data: JSON.stringify({ searchTerm : term }),
    type: "POST",  
    contentType: "application/json",       
    dataType: "JSON",  
    timeout: 600000,
    success: function (result) {
        ajaxCallback(result.d);
    },
    error: function (xhr, status) {
        alert(status + " - " + xhr.responseText);
    }
});

return false;
}

function ajaxCallback(serverResponse) {
    if (serverResponse !== "loadLocations") {
        //jsonData = JSON.parse(serverResponse);
        alert(serverResponse);
    }
    else
        alert("error");
}

C＃

namespace HELP_Testing
{

public partial class _default : System.Web.UI.Page
{
    private static string consumerKey = "key (removed from question)";
    private static string consumerSecret = "secret (removed from question)";

    [WebMethod]
    public static string FoodSearchExample(string searchTerm)
    {
        FoodSearch foodSearch = new FoodSearch(consumerKey, consumerSecret);
        string str = "";

        var response = foodSearch.GetResponseSynchronously(new FoodSearchRequest()
        {
            SearchExpression = searchTerm
        });

        List<Food> foods = new List<Food>();

        if (response.HasResults)
        {               
            Food f;

            foreach (var food in response.foods.food)
            {
               f = new Food();
               f.FoodId = food.food_id;
               f.FoodType = food.food_type;
               f.FoodName = food.food_name;
               foods.Add(f);
            }
        }
        else
            Console.WriteLine("No results from term");

        JavaScriptSerializer serializer = new JavaScriptSerializer();
        str = serializer.Serialize(foods);

        return str;
    }

    protected void Page_Load(object sender, EventArgs e)
    {

    }
}

}

HTML

<%@ Page Language="C#" AutoEventWireup="true" Async="True"  CodeBehind="default.aspx.cs"     Inherits="HELP_Testing._default" %>

<!DOCTYPE html>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">    
    <script type="text/javascript" src="scripts/default.js"></script>
    <script type="text/javascript" src="scripts/jquery-1.11.1.js"></script>
    <title>Healthy Eating Life Planner</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <input type="text" name="Food Search" id="searchField" />
        <button type="submit" onclick="search()">Search</button>
    </div>
    </form>
</body>
</html>

完整的错误消息是：

此时无法启动异步操作。异步操作只能使用异步处理程序或模块启动或者在页面生命周期中的某些事件期间。如果在执行页面时发生此异常，请确保页面被标记为Async = true。此例外还可能表示尝试调用“异步无效”空白＆＃39;方法，一般 ASP.NET请求处理中不受支持。相反，异步方法应该返回一个Task，调用者应该等待它＃34;

Answer 1

是的，the problem is in GetResponseSynchronously。轮询完成是一个非常值得怀疑的方法。

有几种方法可以解决这个问题。一种是抛弃FatSearch CSharp库并使用HttpClient写入他们的JSON API。这种方法更简洁，但意味着您必须编写更多代码。

另一种方法是wrap the sort-of-EBAP APIs from FatSearch CSharp as async-compatible methods。在这种情况下，重要成员是GotResult，GotError和StartRequestAsync。请注意，您的网络方法将变为async。

Answer 2

而不是打电话公共任务GetResponseSynchronously（TRequest请求）就像示例控制台App建议的那样，在像MVC这样的Web上下文中，最好添加一个异步方法，比如我下面成功写的那个：

    /// <summary>
    /// Gets the response Asynchronously.
    /// </summary>
    /// <param name="request">The request.</param>
    /// <returns>A parsed response, or throws an exception.</returns>
    public async Task<TResponse> GetResponseAsynchronously(TRequest request)
    {

        var requestUrl = CreateRequestUrl(request);

        HttpClient APIRequest = new HttpClient();

        var response = await APIRequest.GetAsync(requestUrl).ConfigureAwait(false);

        response.EnsureSuccessStatusCode();

        string downloadedString = await response.Content.ReadAsStringAsync();


        var result = ConvertClientResultString(downloadedString);                      

        return result;
    }

重要的是要注意，要获得无缝结果，您需要通过添加如下所示的响应处理方法来更改Service4u2Lib的BaseJsonService.c：

/// <summary>
    /// Handles the client result string.
    /// </summary>
    /// <param name="downloadedString">The downloaded string.</param>
    public TResultType ConvertClientResultString(string downloadedString)
    {
        // Check for html doctype and report error if found.
        int takeLength = downloadedString.Length > 20 ? 20 : downloadedString.Length;
        if (downloadedString.Substring(0, takeLength).Contains("!DOCTYPE html"))
            HandleClientError(new NotSupportedException("The service call returned html and not json"));

        var result = new TResultType();

        string json = downloadedString;

        if (result is IJSONMassager)
        {
            json = ((IJSONMassager)result).MassageJSON(downloadedString);
        }

        if (result is IJSONSelfSerialize<TResultType>)
        {
            result = ((IJSONSelfSerialize<TResultType>)result).SelfSerialize(json);
        }
        else
            result = JsonHelper.Deserialize<TResultType>(json);

        if (GotResult != null)
            GotResult(this, new EventArgs<TResultType>() { Argument = result });

        return result;
    }

基本上我们重新调整现有对象，使它们可以使用HTTPClient对象，该对象可以使用.ConfigureAwait（false）处理请求。确保回调发生的方法。

调用FatSecret Sharp API时，此时无法启动异步操作

2 个答案: