C# 此时无法启动异步操作。答案

【问题标题】：C# An asynchronous operation cannot be started at this time.C# 此时无法启动异步操作。
【发布时间】：2019-01-11 21:54:13
【问题描述】：

当我单击以asp web 表单提交的按钮时，我正在尝试运行我的代码。单击按钮后立即发生错误有人知道原因吗？错误信息显示如下：

“/”应用程序中的服务器错误。

此时无法启动异步操作。异步操作只能在异步处理程序中启动或模块或页面生命周期中的某些事件期间。如果这执行页面时发生异常，请确保该页面是标记为。

aspx 文件：

<asp:Content ID="BodyContent" ContentPlaceHolderID="MainContent" runat="server">
<div class="jumbotron">
    <h1>Luis</h1>        
        <asp:TextBox ID="TextBox1" runat="server" Height="40px" Width="273px"></asp:TextBox>    
</div>
    <p>
       <input id="Submit1"  runat="server" type="submit" value="Check" onserverclick="Submit_Click"/></p>  
    <p>
    <asp:Label ID="Label1" runat="server" Text="Label"></asp:Label>
</p>
</asp:Content>

.cs 文件：

public partial class _Default : Page
{
public async void Submit1_Click(object sender, EventArgs e) {

    string utterance = TextBox1.Text;

    var client = new HttpClient();
    var queryString = HttpUtility.ParseQueryString(string.Empty);

    // This app ID is for a public sample app that recognizes requests to turn on and turn off lights
    var luisAppId = "75bcaaff-1dc1-4dsa-adf7-63584cea339a";
    var subscriptionKey = "43314f19c5ecgdascba6a00f1d3cc3533";

    // The request header contains your subscription key
    client.DefaultRequestHeaders.Add("Ocp-Apim-Subscription-Key", subscriptionKey);

    // The "q" parameter contains the utterance to send to LUIS
    //queryString["q"] = "turn on the left light";

    // These optional request parameters are set to their default values
    queryString["timezoneOffset"] = "0";
    queryString["verbose"] = "false";
    queryString["spellCheck"] = "false";
    queryString["staging"] = "false";

    var uri = "https://westus.api.cognitive.microsoft.com/luis/v2.0/apps/" + luisAppId + "?" + queryString + "&q=" + utterance;
    var response = await client.GetAsync(uri);

    var strResponseContent = await response.Content.ReadAsStringAsync();

    // Display the JSON result from LUIS
    //Console.WriteLine(strResponseContent.ToString());
    Label1.Text = strResponseContent.ToString();
}
}

【问题讨论】：

标签： c# asp.net asynchronous

【解决方案1】：

您正在调用ASYNC 方法，答案在错误中。

确保页面标记为。

【讨论】：