来自WebMethod的jQuery空白结果

我试图通过jQuery运行webmethod，jQuery将根据一对级联Dropbox的内容查询SQL数据库。我尝试调用该方法，并使用各种jQuery获取结果，有一次使用UpdatePanel尝试使其工作，但在每次尝试结束时，我似乎都停留在同一点上，所有代码运行时都没有错误，但是传递给最终标签文本的结果字符串为空

我猜我可能错过了WebMethod中一些非常基本的东西，并想知道是否有人能为我指出正确的方向：

数据库中名为drivers的目标表有4列：

model\u id，一个整数，应该是ddlModel。选择editem.Value
model，一个varchar（255），应该是ddlModel。选择editem.Text
驱动程序，一个整数（位已尝试，但对问题没有影响，使用inter以允许记录创建页面正确运行），其中包含1或0，用于定义是否应在结果字符串中使用subs字段
subs，一个varchar（255），其中包含在驱动程序为0时要添加到结果字符串中的数据

我没有详细说明用于填充层叠下拉框的表格，因为它们似乎运行正常，但是如果需要此信息或任何其他信息，请毫不犹豫地询问

我的代码如下：

printers.asmx.vb

Imports System.Web
Imports System.Web.Services
Imports System.Web.Services.Protocols
Imports System.Collections
Imports System.Collections.Generic
Imports System.Collections.Specialized
Imports AjaxControlToolkit
Imports System.Data
Imports System.Data.SqlClient
Imports System.Configuration

<WebService(Namespace:="http://printers.mydomainname.com/")> _
<WebServiceBinding(ConformsTo:=WsiProfiles.BasicProfile1_1)> _
<Global.Microsoft.VisualBasic.CompilerServices.DesignerGenerated()> _
<System.Web.Script.Services.ScriptService()> _
Public Class printers
Inherits System.Web.Services.WebService

<WebMethod()> _
Public Function GetMake(ByVal knownCategoryValues As String, ByVal category As String) As CascadingDropDownNameValue()
    Dim strConnection As String = ConfigurationManager.ConnectionStrings("PrinterConnection").ConnectionString
    Dim sqlConn As SqlConnection = New SqlConnection(strConnection)
    Dim strMakeQuery As String = "SELECT * FROM manufacturers ORDER BY make ASC"
    Dim cmdFetchMake As SqlCommand = New SqlCommand(strMakeQuery, sqlConn)

    Dim dtrMake As SqlDataReader
    Dim myMake As New List(Of CascadingDropDownNameValue)

    sqlConn.Open()
    dtrMake = cmdFetchMake.ExecuteReader

    While dtrMake.Read()
        Dim strMakeName As String = dtrMake("make").ToString
        Dim strMakeId As String = dtrMake("make_id").ToString

        myMake.Add(New CascadingDropDownNameValue(strMakeName, strMakeId))
    End While

    Return myMake.ToArray
End Function

<WebMethod()> _
Public Function GetModel(ByVal knownCategoryValues As String, ByVal category As String) As CascadingDropDownNameValue()
    Dim strConnection As String = ConfigurationManager.ConnectionStrings("PrinterConnection").ConnectionString
    Dim sqlConn As SqlConnection = New SqlConnection(strConnection)
    Dim strModelQuery As String = "SELECT * FROM printers WHERE make_id = @makeid"
    Dim cmdFetchModel As SqlCommand = New SqlCommand(strModelQuery, sqlConn)

    Dim dtrModel As SqlDataReader
    Dim kvModel As StringDictionary = CascadingDropDown.ParseKnownCategoryValuesString(knownCategoryValues)

    Dim intMakeId As Integer

    If Not kvModel.ContainsKey("make") Or Not Int32.TryParse(kvModel("make"), intMakeId) Then
        Return Nothing
    End If

    cmdFetchModel.Parameters.AddWithValue("@makeid", intMakeId)
    Dim myModel As New List(Of CascadingDropDownNameValue)

    sqlConn.Open()
    dtrModel = cmdFetchModel.ExecuteReader

    While dtrModel.Read()
        Dim strModelName As String = dtrModel("model").ToString
        Dim strModelId As String = dtrModel("model_id").ToString

        myModel.Add(New CascadingDropDownNameValue(strModelName, strModelId))
    End While

    Return myModel.ToArray
End Function

<WebMethod()> _
Public Function GetDriver(ByVal model As String) As String
    Dim strConnection As String = ConfigurationManager.ConnectionStrings("PrinterConnection").ConnectionString
    Dim sqlConn As SqlConnection = New SqlConnection(strConnection)
    Dim strDriverQuery As String = "SELECT * FROM drivers WHERE model = @model"
    Dim cmdFetchDriver As SqlCommand = New SqlCommand(strDriverQuery, sqlConn)

    Dim dtrDriver As SqlDataReader
    Dim intModel As Integer

    cmdFetchDriver.Parameters.AddWithValue("@model", intModel)
    Dim strResult As String = "The selected printer is"

    sqlConn.Open()
    dtrDriver = cmdFetchDriver.ExecuteReader

    dtrDriver.Read()
    Dim intDriver As Integer = dtrDriver("driver")
    Dim strSubs As String = dtrDriver("subs").ToString

    If intDriver = 1 Then
        strResult = strResult + "fully compatible with the Windows 2003 Hosted platform."
    Else
        strResult = strResult + "supported on the Windows 2003 Hosted platform via a subsituted driver:" + strSubs
    End If

    Return strResult

End Function

End Class

<WebMethod()> _
Public Function GetDriver(ByVal model_id As Integer)
    Dim strConnection As String = ConfigurationManager.ConnectionStrings("PrinterConnection").ConnectionString
    Dim sqlConn As SqlConnection = New SqlConnection(strConnection)
    Dim strDriverQuery As String = "SELECT * FROM drivers WHERE model_id = @model_id"
    Dim cmdFetchDriver As SqlCommand = New SqlCommand(strDriverQuery, sqlConn)

    Dim dtrDriver As SqlDataReader
    Dim intModel As Integer

    cmdFetchDriver.Parameters.AddWithValue("@model_id", intModel)
    cmdFetchDriver.Parameters("@model_id").Value = model_id

    Dim strResult As String = ""

    sqlConn.Open()
    dtrDriver = cmdFetchDriver.ExecuteReader

    dtrDriver.Read()
    Dim intDriver As Integer = dtrDriver("driver")
    Dim strSubs As String = dtrDriver("subs").ToString

    If intDriver = 1 Then
        strResult = "<font color=11CC11>The selected printer is fully compatible.</font>"
    ElseIf intDriver = 0 Then
        strResult = "<font color=FF9933>The selected printer may be compatible via the substitute print driver: " + strSubs + "</font>"
    End If

    Return strResult

End Function

导入系统.Web
导入System.Web.Services
导入System.Web.Services.Protocols
导入系统集合
导入System.Collections.Generic
导入System.Collections.Specialized
导入AjaxControlToolkit
导入系统数据
导入System.Data.SqlClient
导入系统配置
_
_
_
_
公共类打印机
继承System.Web.Services.WebService
_
公共函数GetMake（ByVal knownCategoryValues为字符串，ByVal category为字符串）为CascadingDropDownNameValue（）
Dim strConnection As String=ConfigurationManager.ConnectionString（“PrinterConnection”）.ConnectionString
Dim sqlConn As SqlConnection=新SqlConnection（strConnection）
Dim strMakeQuery As String=“按制造商ASC从制造商订单中选择*”
Dim cmdFetchMake As SqlCommand=新SqlCommand（strMakeQuery，sqlConn）
将DTR设置为SqlDataReader
Dim myMake作为新列表（CascadingDropDownNameValue的）
sqlConn.Open（）
dtrMake=cmdFetchMake.ExecuteReader
而dtrMake.Read（）
Dim strMakeName As String=dtrMake（“制造”）.ToString
Dim strMakeId As String=dtrMake（“make_id”）。ToString
添加（新的cascadingdropdownname值（strMakeName，strMakeId））
结束时
返回我的make.ToArray
端函数
_
公共函数GetModel（ByVal knownCategoryValues为字符串，ByVal category为字符串）为CascadingDropDownNameValue（）
Dim strConnection As String=ConfigurationManager.ConnectionString（“PrinterConnection”）.ConnectionString
Dim sqlConn As SqlConnection=新SqlConnection（strConnection）
Dim strModelQuery As String=“从打印机中选择*，其中make_id=@makeid”
Dim cmdFetchModel As SqlCommand=新的SqlCommand（strModelQuery，sqlConn）
将dtrModel设置为SqlDataReader
Dim kvModel As StringDictionary=CascadingDropDown.ParseKnownCategoryValuesString（knownCategoryValues）
Dim intMakeId为整数
如果不是kvModel.ContainsKey（“make”）或不是Int32.TryParse（kvModel（“make”），intMakeId），那么
一无所获
如果结束
cmdFetchModel.Parameters.AddWithValue（“@makeid”，intMakeId）
Dim myModel作为新列表（CascadingDropDownNameValue）
sqlConn.Open（）
dtrModel=cmdFetchModel.ExecuteReader
而dtrModel.Read（）
Dim strModelName作为字符串=dtrModel（“模型”）。ToString
Dim STRMODEL As String=dtrModel（“模型id”）。ToString
添加（新的CascadingDropDownNameValue（strModelName，strModelId））
结束时
返回myModel.ToArray
端函数
_
公共函数GetDriver（ByVal模型为字符串）为字符串
Dim strConnection As String=ConfigurationManager.ConnectionString（“PrinterConnection”）.ConnectionString
Dim sqlConn As SqlConnection=新SqlConnection（strConnection）
Dim strDriverQuery As String=“从驱动程序中选择*，其中model=@model”
Dim cmdFetchDriver As SqlCommand=新SqlCommand（strDriverQuery，sqlConn）
Dim dtrDriver作为SqlDataReader
整数模型
cmdFetchDriver.Parameters.AddWithValue（“@model”，intModel）
Dim strResult As String=“所选打印机为”
sqlConn.Open（）
dtrDriver=cmdFetchDriver.ExecuteReader
dtrDriver.Read（）
Dim intDriver作为整数=dtrDriver（“驱动程序”）
Dim strSubs As String=dtrDriver（“subs”）。ToString
如果intDriver=1，则
strResult=strResult+“与Windows 2003托管平台完全兼容。”
其他的
strResult=strResult+“通过替代驱动程序在Windows 2003托管平台上受支持：”+strSubs
如果结束
返回strResult
端函数
末级

default.aspx

<%@ Page Language="VB" AutoEventWireup="false" EnableEventValidation="false" Inherits="Printer_Compatibility_Matrix_VB._Default" Codebehind="Default.aspx.vb" %>

<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="cc1" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">

<title>Printer Compatibility Matrix</title>
<script src="jquery-1.4.4.min.js" type="text/javascript"></script>
<script language="javascript" type="text/javascript">
    function CallService() {
        $.ajax({
            type: "POST",
            url: "printers.asmx/GetDriver",
            data: $("#ddlModel option:selected").text(),
            contentType: "application/json; charset=utf-8",
            dataType: "json",
            success: OnSuccess,
            error: OnError
        });
    }

    function OnSuccess(data, status) {
        $("#lblResult").html(data.d);
    }

    function OnError(request, status, error) {
        $("#lblResult").html(request.statusText);
    }
</script>

</head>
<body>        

<form id="form1" runat="server">
<asp:ScriptManager ID="ScriptManager1" runat="server" EnablePageMethods = "true">
    <Services>
        <asp:ServiceReference Path="printers.asmx" />
    </Services>
</asp:ScriptManager>
<div>

    Manufacturer:  <asp:DropDownList ID="ddlMake" runat="server" Width="170" /><br />
    Printer:  <asp:DropDownList ID="ddlModel" runat="server" Width="170" /><br />

    <asp:Button ID="btnDriver" Text="Submit" OnClientClick="CallService(); return false;" runat="server" />
    <asp:Label ID="lblResult" Text="&nbsp;" Width="100%" runat="server" />


    <cc1:CascadingDropDown 
        id="CascadingDropDown1" 
        runat="server"
        category="Make"
        prompttext="Select a Manufacturer..."
        ServiceMethod="GetMake"
        ServicePath="printers.asmx"
        TargetControlId="ddlMake"
    />

    <cc1:CascadingDropDown 
        id="CascadingDropDown2" 
        runat="server" 
        category="Model"
        prompttext="Select a Printer..." 
        ServiceMethod="GetModel" 
        ServicePath="printers.asmx"
        TargetControlId="ddlModel"
        ParentControlId="ddlMake"
    />      
</div>
</form>
</body>
</html>

<script src="jquery-1.4.4.min.js" type="text/javascript"></script>
<script language="javascript" type="text/javascript">
    function CallService() {
        $.ajax({
            type: "POST",
            url: "printers.asmx/GetDriver",
            data: "{ 'model_id': " + $("#ddlModel :selected").val() + "}",
            contentType: "application/json; charset=utf-8",
            dataType: "json",
            success: OnSuccess,
            error: OnError
        });
    }

    function OnSuccess(data, status) {
        $("#lblResult").html(data);
    }

    function OnError(request, status, error) {
        $("#lblResult").html("<font color=#FF0000>Please make a valid selection.<font>");
    }
</script>

打印机兼容性矩阵
函数CallService（）{
$.ajax({
类型：“POST”，
url:“printers.asmx/GetDriver”，
数据：$（“#ddlModel选项：选中”）.text（），
contentType:“应用程序/json；字符集=utf-8”，
数据类型：“json”，
成功：一旦成功，
错误：OnError
});
}
成功时的功能（数据、状态）{
$（“#lblResult”）.html（data.d）；
}
函数OnError（请求、状态、错误）{
$（“#lblResult”）.html（request.statusText）；
}
制造商：

打印机：

非常感谢您抽出时间

吉姆

编辑

似乎除了Frédéric发现的错误之外，我还忘记了引用jQuery，我已经修改了上面的代码以匹配我的curr