首先介紹一下我在調用微信支付接口使用的是 weixin.senparc SDK，非常方便好用開源的一個微信開發SDK。

weixin.senparc SDK 官網：http://weixin.senparc.com/

先去下載下來Senparc.Weixin SDK。

在調起支付接口之前，需要先要調用統一下單接口，商戶系統先調用該接口在微信支付服務后臺生成預支付交易單，返回正確的預支付交易回話標識后再在APP里面調起支付。

 微信 JsApi支付 在這個目錄下 Senparc.Weixin.MP.Sample.Controllers 找到JsApi支付。

public ActionResult JsApi(string code, string state)  {   if (string.IsNullOrEmpty(code))   {    return Content("您拒絕了授權！");   }   if (!state.Contains("|"))   {    //這里的state其實是會暴露給客戶端的，驗證能力很弱，這里只是演示一下    //實際上可以存任何想傳遞的數據，比如用戶ID，并且需要結合例如下面的Session["OAuthAccessToken"]進行驗證    return Content("驗證失敗！請從正規途徑進入！1001");   }   try   {    //獲取產品信息    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，或非法進入！1002");      }      ViewData["product"] = product;     }    }    //通過，用code換取access_token    var openIdResult = OAuthApi.GetAccessToken(TenPayV3Info.AppId, TenPayV3Info.AppSecret, code);    if (openIdResult.errcode != ReturnCode.請求成功)    {     return Content("錯誤：" + openIdResult.errmsg);    }    string sp_billno = Request["order_no"];    if (string.IsNullOrEmpty(sp_billno))    {     //生成訂單10位序列號，此處用時間和隨機數生成，商戶根據自己調整，保證唯一     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);//調用統一訂單接口    //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);   }  }