c# - 我在 asp.net MVC 中进行 session 处理它适用于 View 页面按钮我无法在 Controller 中的另一个操作上获取 session

Question

这个问题在这里已经有了答案:





What is a NullReferenceException, and how do I fix it?

(27 个回答)


2个月前关闭。




我从这个 Controller 的数据库中获取数据，然后我将用户名存储到一个 session 中，当我在登录后移动到 View 页面时它可以工作。

public ActionResult shoppage(assign s)
{

    if (ModelState.IsValid)
    {
        using (transactionEntities db = new transactionEntities())
        {
            var obj = db.assigns.Where(a => a.Username.Equals(s.Username) && a.Password.Equals(s.Password)).FirstOrDefault();
            if (obj != null)
            {
                Session["Username"] = s.Username.ToString();

                return View();
            }
            else
            {
                return RedirectToAction("login");
            }
        }

但是当我尝试在另一个操作结果中访问它时，它给了我一个空值异常

public ActionResult insertwatch()
{
    if (Session["Username"] != null)
    {
        name = Session["Username"].ToString();
    }

    if (Request.Form["submit1"] != null)
    {
        transactionEntities dt = new transactionEntities();
        itemthing it = new itemthing();
        it.uname = name.ToString();
        it.itemprice = "1200";
        it.itemname = "lucia";
        dt.itemthings.Add(it);
        return RedirectToAction("shoppage");
    }
    else if (Request.Form["submit2"] != null)
    {
        transactionEntities dt = new transactionEntities();
        itemthing it = new itemthing();
        it.uname = name.ToString();
        it.itemprice = "1800";
        it.itemname = "Benson";
        dt.itemthings.Add(it);
        return RedirectToAction("shoppage");
    }

错误:

Answer 1

您可能需要添加一个空检查属性:-

 public ActionResult shoppage(assign s)
    {

        if (ModelState.IsValid)
        {
            using (transactionEntities db = new transactionEntities())
            {
                var obj = db.assigns.Where(a => a.Username.Equals(s.Username) && a.Password.Equals(s.Password)).FirstOrDefault();
                if (obj != null)
                {
                     if (HttpContext.Current.Session["Username"] == null)  //add this code
                          return string.Empty;
                    else
                        //Session["Username"] = s.Username.ToString();
                        HttpContext.Current.Session["Username"] = s.Username.ToString();

                    return View();
                }
                else
                {
                    return RedirectToAction("login");
                }
            }

或者你可以简单地使用这行代码:-

//clarify code

if (Session["Username"]!=null)
{
   Session["Username"] = s.Username.ToString();
   return View();
}

//clarify code

或者您可以使用类似设置 session 的内容并获取 session 的存储值:-
设置 session

string user = s.Username.ToString();   
HttpContext.Session.SetString("UserToken", user);

从 session 中获取存储的值:-

var token = HttpContext.Session.GetString("UserToken");

我认为它会解决你的问题。