public ActionResult JsApi(string code, string state)
  {
   if (string.IsNullOrEmpty(code))
   {
    return Content("您拒绝了授权！");
   }

   if (!state.Contains("|"))
   {
    //这里的state其实是会暴露给客户端的，验证能力很弱，这里只是演示一下
    //实际上可以存任何想传递的数据，比如用户ID，并且需要结合例如下面的Session["OAuthAccessToken"]进行验证
    return Content("验证失败！请从正规途径进入！1001");
   }
   try
   {


    //获取产品信息
    var stateData = state.Split('|');
    int productId = 0;
    ProductModel product = null;
    if (int.TryParse(stateData[0], out productId))
    {
     int hc = 0;
     if (int.TryParse(stateData[1], out hc))
     {
      var products = ProductModel.GetFakeProductList();
      product = products.FirstOrDefault(z => z.Id == productId);
      if (product == null || product.GetHashCode() != hc)
      {
       return Content("商品信息不存在，或非法进入！1002");
      }
      ViewData["product"] = product;
     }
    }

    //通过，用code换取access_token
    var openIdResult = OAuthApi.GetAccessToken(TenPayV3Info.AppId, TenPayV3Info.AppSecret, code);
    if (openIdResult.errcode != ReturnCode.请求成功)
    {
     return Content("错误：" + openIdResult.errmsg);
    }

    string sp_billno = Request["order_no"];
    if (string.IsNullOrEmpty(sp_billno))
    {
     //生成订单10位序列号，此处用时间和随机数生成，商户根据自己调整，保证唯一
     sp_billno = string.Format("{0}{1}{2}", TenPayV3Info.MchId, DateTime.Now.ToString("yyyyMMdd"),
      TenPayV3Util.BuildRandomStr(10));
    }
    else
    {
     sp_billno = Request["order_no"];
    }

    var timeStamp = TenPayV3Util.GetTimestamp();
    var nonceStr = TenPayV3Util.GetNoncestr();

    var body = product == null ? "test" : product.Name;
    var price = product == null ? 100 : product.Price * 100;
    var xmlDataInfo = new TenPayV3UnifiedorderRequestData(TenPayV3Info.AppId, TenPayV3Info.MchId, body, sp_billno, price, Request.UserHostAddress, TenPayV3Info.TenPayV3Notify, TenPayV3Type.JSAPI, openIdResult.openid, TenPayV3Info.Key, nonceStr);
    var result = TenPayV3.Unifiedorder(xmlDataInfo);//调用统一订单接口

    //JsSdkUiPackage jsPackage = new JsSdkUiPackage(TenPayV3Info.AppId, timeStamp, nonceStr,);
    var package = string.Format("prepay_id={0}", result.prepay_id);

    ViewData["appId"] = TenPayV3Info.AppId;
    ViewData["timeStamp"] = timeStamp;
    ViewData["nonceStr"] = nonceStr;
    ViewData["package"] = package;
    ViewData["paySign"] = TenPayV3.GetJsPaySign(TenPayV3Info.AppId, timeStamp, nonceStr, package, TenPayV3Info.Key);

    return View();
   }
   catch (Exception ex)
   {
    var msg = ex.Message;
    msg += "<br>" + ex.StackTrace;
    msg += "<br>==Source==<br>" + ex.Source;

    if (ex.InnerException != null)
    {
     msg += "<br>===InnerException===<br>" + ex.InnerException.Message;
    }
    return Content(msg);
   }
  }

<xml>
<return_code><![CDATA[FAIL]]></return_code>
<return_msg><![CDATA[您没有JSAPI支付权限]]></return_msg>
</xml>

<xml>
<return_code><![CDATA[FAIL]]></return_code>
<return_msg><![CDATA[商户号mch_id与appid不匹配]]></return_msg>
</xml>

<xml>
<return_code><![CDATA[FAIL]]></return_code>
<return_msg><![CDATA[appid and openid not match]]></return_msg>
</xml>

<xml>
<return_code><![CDATA[FAIL]]></return_code>
<return_msg><![CDATA[openid is invalid]]></return_msg>
</xml>

<xml>
 <return_code><![CDATA[SUCCESS]]></return_code>
 <return_msg><![CDATA[OK]]></return_msg>
 <appid><![CDATA[wx2421b1c4370ec43b]]></appid>
 <mch_id><![CDATA[10000100]]></mch_id>
 <nonce_str><![CDATA[IITRi8Iabbblz1Jc]]></nonce_str>
 <sign><![CDATA[7921E432F65EB8ED0CE9755F0E86D72F]]></sign>
 <result_code><![CDATA[SUCCESS]]></result_code>
 <prepay_id><![CDATA[wx201411101639507cbf6ffd8b0779950874]]></prepay_id>
 <trade_type><![CDATA[APP]]></trade_type>
</xml>

 ViewData["appId"] = TenPayV3Info.AppId;
    ViewData["timeStamp"] = timeStamp;
    ViewData["nonceStr"] = nonceStr;
    ViewData["package"] = package;
    ViewData["paySign"] = TenPayV3.GetJsPaySign(TenPayV3Info.AppId, timeStamp, nonceStr, package, TenPayV3Info.Key);

wx.chooseWXPay({
 timestamp: 0, // 支付签名时间戳，注意微信jssdk中的所有使用timestamp字段均为小写。但最新版的支付后台生成签名使用的timeStamp字段名需大写其中的S字符
 nonceStr: '', // 支付签名随机串，不长于 32 位
 package: '', // 统一支付接口返回的prepay_id参数值，提交格式如：prepay_id=***）
 signType: '', // 签名方式，默认为'SHA1'，使用新版支付需传入'MD5'
 paySign: '', // 支付签名
 success: function (res) {
  if (res.err_msg == "get_brand_wcpay_request:ok") {//支付成功
 
  } else {
   //支付失败

  }
  // 使用以上方式判断前端返回,微信团队郑重提示：res.err_msg将在用户支付成功后返回ok，但并不保证它绝对可靠。
 }
});