动态生成的下拉列表中断web服务调用

Question

我有一个ASPX下拉列表，用于web服务调用以生成图。

如果我手动输入下拉列表条目，代码执行良好，但是如果我从SQL服务器动态生成下拉列表，则web服务调用失败。

以下是我如何生成下拉列表：

//Populate Customers DDL
string constr = ConfigurationManager.ConnectionStrings["Indigo2.Properties.Settings.ConstrNW"].ConnectionString;
DataTable customers = new DataTable();
using (SqlConnection con = new SqlConnection(constr))
{
try
{
SqlDataAdapter adapter = new SqlDataAdapter("SELECT DISTINCT custid from [Indigo].[dbo].[invoices] WHERE custid='ACC001'", con);
adapter.Fill(customers);
//ddlCustA.DataSource = customers;
//ddlCustA.DataTextField = "custid";
//ddlCustA.DataValueField = "custid";
//ddlCustA.DataBind();
}
catch (Exception ex)
{
// Handle the error
}
}

这是HTML

<asp:DropDownList ID="ddlCustA" runat="server" Height="17px" Width="100px" AutoPostBack="True">
</asp:DropDownList>

这就是我称之为网络服务的地方

//Code for graph (all in document ready)
$("#btn_line_chart").on('click', function () {
var CustA = $("#ddlCustA").val();
var CustB = $("#ddlCustB").val();
var getYear = $("#ddlYear").val();
var jsonData = JSON.stringify({
custA: CustA,
custB: CustB,
year: getYear
});
$.ajax({
type: "POST",
url: "WebService1.asmx/getLineChartData",
data: jsonData,
contentType: "application/json; charset=utf-8",
dataType: "json",
success: OnSuccess_,
error: OnErrorCall_
});
function OnSuccess_(reponse) {
var aData = reponse.d;
var aLabels = aData[0];
var aDatasets1 = aData[1];
var aDatasets2 = aData[2];
var data = {
labels: aLabels,
datasets: [{
label: "My First dataset",
fillColor: "rgba(220,220,220,0.2)",
strokeColor: "rgba(220,220,220,1)",
pointColor: "rgba(220,220,220,1)",
pointStrokeColor: "#fff",
pointHighlightFill: "#fff",
pointHighlightStroke: "rgba(220,220,220,1)",
data: aDatasets1
},
{
label: "My Second dataset",
fillColor: "rgba(151,187,205,0.2)",
strokeColor: "rgba(151,187,205,1)",
pointColor: "rgba(151,187,205,1)",
pointStrokeColor: "#fff",
pointHighlightFill: "#fff",
pointHighlightStroke: "rgba(151,187,205,1)",
data: aDatasets2
}]
};
var ctx = $("#myChart").get(0).getContext('2d');
ctx.canvas.width = 750; // setting width of canvas
ctx.canvas.height = 400;  // setting height of canvas
var lineChart = new Chart(ctx, {
type: "line",
data: data,
bezierCurve: false
});
}
function OnErrorCall_(repo) {
alert("Woops something went wrong, pls try later !");
}
});

如果我手动选择下拉列表选项(如下所示(，效果会很好。

<select id="ddlCustA">
<option>ACC001</option>
</select>

当从SQL服务器生成下拉列表时，web服务调用失败，并出现以下错误：

HTTP500:SERVER错误-服务器遇到意外情况这使它无法满足请求。(XHR(岗位-https://localhost:44338/WebService1.asmx/getLineChartData

非常感谢您的帮助。

更新：这似乎是一个时间问题。如果我在web服务调用ddlCustA变量之前添加警报，则ddlCustA显示为"未定义">

alert($("#ddlCustA").val());

Answer 1

如果它能帮助其他人，我的解决方案是从Javasctipt调用对象的方式。下面的代码修复了它。

var CustA = document.getElementById('<%= ddlCustA.ClientID %>').value