Asp.net 3.5和JSON中的Web服务

Question

I have a Web Service in ASP.Net 3.5 and I can not properly generate a JSON. The formatting is correct, but still does not work when trying to access $. Ajax. My suspicion is that the header remains as xml and I'm not understanding why. The following code:

WEB SERVICE:

Imports System.Web
Imports System.Web.Services
Imports System.Web.Services.Protocols
Imports System.Data
Imports System.IO
Imports System.Runtime.Serialization.Json

<System.Runtime.Serialization.DataContractAttribute()> _
Public Class Estado

    Dim _ID As Integer = 0
    <System.Runtime.Serialization.DataMemberAttribute()> _
    Public Property ID() As Integer
        Get
            Return _ID
        End Get
        Set(value As Integer)
            _ID = value
        End Set
    End Property

    Dim _Descricao As String = ""
    <System.Runtime.Serialization.DataMemberAttribute()> _
    Public Property Descricao() As String
        Get
            Return _Descricao
        End Get
        Set(value As String)
            _Descricao = value
        End Set
    End Property

    Dim _UF As String
    <System.Runtime.Serialization.DataMemberAttribute()> _
    Public Property UF() As String
        Get
            Return _UF
        End Get
        Set(value As String)
            _UF = value
        End Set
    End Property

End Class

' To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line.
' <System.Web.Script.Services.ScriptService()> _
<WebService(Namespace:="http://tempuri.org/")> _
<WebServiceBinding(ConformsTo:=WsiProfiles.BasicProfile1_1)> _
<Global.Microsoft.VisualBasic.CompilerServices.DesignerGenerated()> _
Public Class Service
    Inherits System.Web.Services.WebService

    <WebMethod()> _
    Public Function HelloWorld() As String
        Return "Hello World"
    End Function

    <WebMethod()> _
    <Script.Services.ScriptMethod(ResponseFormat:=System.Web.Script.Services.ResponseFormat.Json)> _
    Public Function getStates() As String
        Try
            Dim ds As New System.Data.DataSet

            Dim strConexao As String = ""
            strConexao = ConfigurationManager.ConnectionStrings("ConnectionString").ConnectionString

            Dim conexao As System.Data.SqlClient.SqlConnection = New Data.SqlClient.SqlConnection()
            conexao.ConnectionString = strConexao
            conexao.Open()

            Dim cmd As System.Data.SqlClient.SqlCommand = New Data.SqlClient.SqlCommand
            cmd.CommandText = "Select ID, Descricao, UF From dbo.States"
            cmd.CommandTimeout = 120
            cmd.Connection = conexao

            Dim adp As System.Data.SqlClient.SqlDataAdapter = New Data.SqlClient.SqlDataAdapter()
            adp.SelectCommand = cmd
            adp.Fill(ds)

            Dim obj As List(Of Estado) = New List(Of Estado)
            For Each dr As DataRow In ds.Tables(0).Rows
                Dim e As Estado = New Estado()
                e.ID = dr.Item("ID")
                e.Descricao = dr.Item("Descricao")
                e.UF = dr.Item("UF")

                obj.Add(e)
            Next

            Dim strRetorno As String = getJSON(obj)


            Return strRetorno
        Catch ex As Exception
            Return "Deu Merda: " + ex.Message
        End Try

    End Function

    Private Function getJSON(obj As Object) As String
        'yourobject is your actual object you want to serialize to json
        Dim serializer As DataContractJsonSerializer = New DataContractJsonSerializer(obj.GetType())

        'create a memory stream
        Dim ms As MemoryStream = New MemoryStream()

        'serialize the object to memory stream
        serializer.WriteObject(ms, obj)

        'convert the serizlized object to string
        Dim jsonString As String = Encoding.Default.GetString(ms.ToArray())

        'close the memory stream
        ms.Close()

        Return jsonString
    End Function
End Class

Web Page:

<%@ Page Language="vb" AutoEventWireup="false" CodeBehind="Default.aspx.vb" Inherits="WS_JSON_Teste._Default" %>

<!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 runat="server">
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
    <div>

    </div>
    </form>
</body>

<link rel="stylesheet" href="http://code.jquery.com/ui/1.8.22/themes/base/jquery-ui.css" type="text/css" media="all" />
<link rel="stylesheet" href="http://static.jquery.com/ui/css/demo-docs-theme/ui.theme.css" type="text/css" media="all" />
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js" type="text/javascript"></script>
<script src="http://code.jquery.com/ui/1.8.22/jquery-ui.min.js" type="text/javascript"></script>

<script type="text/javascript">
    $(document).ready(function ($) {
        $.ajax({
            type: "POST",
            url: "http://localhost:27916/WS_JSON/Service.asmx/getStates",
            contentType: "application/jsonp; charset=utf-8",
            dataType: "jsonp",
            success: function (data) {
                alert("success!");
            },
            failure: function (error) {
                alert("failure!");
            }
        });
    });

</script>

I used this link as a reference.

Answer 1

First off... ASMX is current technology that works just fine. ALWAYS ignore people who say "that's old so it won't work"

Secondly, you're doing the serialization yourself and that's what is causing the problem. You don't have to do that. If your request is done properly, and the service knows you want JSON, all you have to do is return the object, and it will convert it to JSON for you.

See this post: http://encosia.com/asp-net-web-services-mistake-manual-json-serialization/

Your web service basically can end up looking like this:

Public Function getStates() as List(Of Estado)
  Dim myStates as List(Of Estado)

  //do the SQL to create the List object - same as above
  //then just do this!
  return myStates
End

That will be much easier!

Let me know if there's something you don't understand after reading the article. I'm happy to add more details if it will help. I have services running this way right now, so I know they work, and they aren't obsolete.