纯 JavaScript 调用 ASP .NET WebService 返回 0

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【中文标题】纯 JavaScript 调用 ASP .NET WebService 返回 0【英文标题】：Pure JavaScript call ASP .NET WebService returns 0 【发布时间】：2018-02-27 12:23:53 【问题描述】：

我实现了一个简单的 ASP.NET WebService，并尝试执行函数并获取返回数据。但是 ajax 调用总是返回状态 0 和 responseText 'undefined'。

我将我的 WebService 置于调试模式，我查看了正确发送的数据，但我没有返回。

我看了很多关于 return 0 的帖子，但我没有找到任何解决方案。

有什么问题吗？非常感谢！

网络服务代码：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Services;
using System.Web.Services.Protocols;
using System.Xml.Linq;

namespace WebServiceDA

    /// <summary>
    /// Summary description for WebService1
    /// </summary>
    [WebService(Namespace = "http://tempuri.org/")]
    [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
    [System.ComponentModel.ToolboxItem(false)]
    // To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line. 
    [System.Web.Script.Services.ScriptService]
    public class WebService1 : System.Web.Services.WebService
    
        //inicialização da estrutura do E3DataAccess
        E3DATAACCESSLib.E3DataAccessManagerClass E3Da = null;

        public WebService1()
        
            //inicializa a conexão com o E3DataAccess
            try
            
                E3Da = new E3DATAACCESSLib.E3DataAccessManagerClass();
            
            catch(Exception ex)
            
                Console.Write(ex.ToString());
            
        

        [WebMethod]
        public string HelloWorld()
        
            return "Hello World";
        

        [WebMethod]
        public string ReadValue(string ObjectName)
        
            object dt = null, v = null, q = null;
            if(E3Da.ReadValue("Dados." +ObjectName, ref dt, ref q, ref v))
                return v.ToString();
            
            return "Invalid Object Name";

html 代码：

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <title>WebService with E3DataAccess</title>

        <script type="text/javascript" src="accessWs.js"></script>
    </head>

    <body>
        <h1> WebService E3DataAccess</h1>
        <p> Exemplo de um cliente html que acessa métodos de um webservice que contém um E3DataAccess</p>

        <div style="background-color:#FFFFFF" id="content">
            <span>Tag Name:</span>
            <input type="text" name="tagname" id="tagname">
            <input type="button" value="Get Tag Value" onclick="CallWs();"
        </div>
    </body>
</html>

JavaScript 代码：

var ajax;

function CreateAjaxObject()
    if(window.XMLHttpRequest) //navegadores modernos
        ajax = new XMLHttpRequest();
    
    else if(window.ActiveXObject) //IE antigao
        ajax = new ActiveXObject("Msxml2.XMLHTTP");
        if(!ajax)
            ajax = new ActiveXObject("Microsoft.XMLHTTP");
        
    
    if(!ajax) //caso não tenha sido iniciado com sucesso
        alert("seu navegador não possui suporte");
    


function SendData(url,dados,AjaxResponseFunction)
    CreateAjaxObject();
    if(ajax)

        //método http
        ajax.open("POST",url,true);

        //definir o encode do conteúdo
        ajax.setRequestHeader('Content-Type',"application/x-www-form-urlencoded");

        //tamanho dos dados
        ajax.setRequestHeader('Content-Length',dados.length);

        //enviar os dados 
        alert(dados);
        ajax.send(dados);

        //retorno
        ajax.onreadystatechange  = function()
            if(ajax.readyState==4) //documento está pronto
                alert(ajax.status);
                AjaxResponseFunction(ajax.status,ajax.ResponseText);
            
        ;

    


function CallWs()
    var dados = '';
    dados = 'ObjectName=' + encodeURIComponent(tagname.value);

    //chamar um webservice = endereço/nomemétodo
    SendData('http://localhost:53626/WebService.asmx/ReadValue',dados,AjaxResponseFunction);


function AjaxResponseFunction(status,response)
    var divR = document.getElementById('content');
    if(ajax.status != 200)
        divR.style.backgroundColor = "#FF0000"; //erro vermelho
    
    else
        divR.style.backgroundColor = "#FFFFFF"; //ok branco

【问题讨论】：

我会将ajax.send(dados); 移到分配事件处理程序后 (ajax.onreadystatechange) 我也试试这个。不工作。谢谢！ 【参考方案1】：

我找到了解决方案。我在 Web.config 文件中添加了一个简单的代码：

<system.webServer>
    <handlers>
      <remove name="ExtensionlessUrlHandler-Integrated-4.0" />
      <remove name="OPTIONSVerbHandler" />
      <remove name="TRACEVerbHandler" />
      <add name="ExtensionlessUrlHandler-Integrated-4.0" path="*." verb="*" type="System.Web.Handlers.TransferRequestHandler" preCondition="integratedMode,runtimeVersionv4.0" />
    </handlers>

    <!-- bellow, code used to fix the security problem-->
        <httpProtocol>
          <customHeaders>
            <add name="Access-Control-Allow-Origin" value="*" />
          </customHeaders>
        </httpProtocol>
    <!-- end code -->

  </system.webServer></configuration>

【讨论】：

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