在 JSON 响应中有奇怪的 {"d":null}

Question

请按如下方式对 Web API 进行 AJAX 调用

$.ajax({
         type: "POST",
         url: "CustomerService.asmx/GetAccounts",
         data: '{"custid":"' + cusID + '"}',
         contentType: "application/json; charset-utf-8",
         dataType: "json",
         success: function (data) {
             datatableVariable = $('#dtAccounts').DataTable({.......

这是我的 ASP.NET Web 方法

<WebMethod()>
Public Sub GetAccounts(ByVal custid As Integer)


    Dim sql As String = "Select * from Accounts WHERE CustomerID =" & custid & " Order by ID"

    Dim constr As String = ConfigurationManager.ConnectionStrings("flashCon").ConnectionString
    Dim accs = New List(Of Accounts)()
    Using con As New SqlConnection(constr)
        Using cmd As New SqlCommand(sql)
            cmd.CommandType = CommandType.Text
            cmd.Connection = con
            con.Open()
            Dim dr = cmd.ExecuteReader()
            If dr.HasRows Then
                While dr.Read
                    Dim acc = New Accounts() With {
                   .custID = Convert.ToInt32(dr("CustomerID").ToString()),
                    .AccNum = dr("AccountNumber").ToString(),
                    .Descri = dr("Description").ToString(),
                    .CurrBalance = dr("CurrentBalance").ToString(),
                    .typOA = dr("TypeOfAccount").ToString(),
                    .Frozen = dr("Frozen").ToString()
                    }
                    accs.Add(acc)
                End While
            End If
        End Using
    End Using
    Dim js = New JavaScriptSerializer()
    Dim strResponse As String = js.Serialize(accs)
    Context.Response.Write(strResponse)
End Sub

返回的 JSON 字符串响应如下所示，带有额外的奇怪 {"d":null} 值，我不知道它来自哪里

[{"custID":2,"AccNum":"KODSW00002","Descri":"","CurrBalance":0,"Frozen":false,"typOA":0}]{"d":null}

如果我使用Context.Response.Flush()，它会消失，然后我从浏览器Server cannot clear headers after HTTP headers have been sent. 收到另一个错误

请有人帮我解决这个问题，已经这样做了好几个星期了

非常感谢

Answer 1

JavascriptSerializer 已弃用。它是在大多数事实上的 JSON 标准之前创建的，当然在任何实际标准之前。例如，它不使用事实上的 ISO8601 日期格式。

微软的own documentation在最上面说：

Json.NET 应该使用序列化和反序列化。为支持 AJAX 的应用程序提供序列化和反序列化功能。

微软自己在 ASP.NET MVC Web API 中使用 Json.NET。

使用Json.NET ，您可以使用 JsonConvert.Serialize 从对象列表中生成 Json 字符串：

Dim strResponse As String = JsonConvert.Serialize(accs)

Answer 2

在使用Context.Response.Clear()在服务器端给出响应之前，我们必须从 ASP.NET Webservice 中清除默认响应 {d:null} 并设置contentType

Context.Response.Clear()
Context.Response.ContentType = "application/json"
Context.Response.AddHeader("content-length", stringJSON.Length.ToString())
Context.Response.Flush()
Context.Response.Write(stringJSON)
HttpContext.Current.ApplicationInstance.CompleteRequest()

Answer 3

试试这个

$.ajax({
     type: "POST",
     url: "CustomerService.asmx/GetAccounts",
     data: {custid: cusID},
     dataType: "json",
     success: function (data) {
         alert(data.d); // Should correctly get the response in the d variable.

秘诀在于 JavaScriptSerializer 不需要 contentType: "应用程序/json; charset-utf-8",

并且在数据中直接写入不带撇号或双引号的参数

更多信息在：https://www.youtube.com/watch?v=Zq_aMDFeCCA

问候

Answer 4

您得到 {"d":null} 因为您的 WebMethod 没有返回值，您只是在写入 Response 对象。

你应该从你的方法中返回一个字符串：

Public Sub GetAccounts(ByVal custid As Integer) As String

Dim sql As String = "Select * from Accounts WHERE CustomerID =" & custid & " Order by ID"

Dim constr As String = ConfigurationManager.ConnectionStrings("flashCon").ConnectionString
Dim accs = New List(Of Accounts)()
Using con As New SqlConnection(constr)
    Using cmd As New SqlCommand(sql)
        cmd.CommandType = CommandType.Text
        cmd.Connection = con
        con.Open()
        Dim dr = cmd.ExecuteReader()
        If dr.HasRows Then
            While dr.Read
                Dim acc = New Accounts() With {
               .custID = Convert.ToInt32(dr("CustomerID").ToString()),
                .AccNum = dr("AccountNumber").ToString(),
                .Descri = dr("Description").ToString(),
                .CurrBalance = dr("CurrentBalance").ToString(),
                .typOA = dr("TypeOfAccount").ToString(),
                .Frozen = dr("Frozen").ToString()
                }
                accs.Add(acc)
            End While
        End If
    End Using
End Using
Dim js = New JavaScriptSerializer()
Dim strResponse As String = js.Serialize(accs)

<strike>Context.Response.Write(strResponse)</strike>

替换为：

Return strResponse

End Sub

然后返回的对象将是 {"d": "[{"custID":2,"AccNum":"KODSW00002","Descri":"","CurrBalance":0,"Frozen":false ,"typOA":0}]"}，可以通过 javascript 中的 response.d 访问。

$.ajax({
         type: "POST",
         url: "CustomerService.asmx/GetAccounts",
         data: '{"custid":"' + cusID + '"}',
         contentType: "application/json; charset-utf-8",
         dataType: "json",
         success: function (data) {
             alert(data.d); // Should correctly get the response in the d variable.

https://stackoverflow.com/a/20471116/4008833