Question

我有vb.net网络应用程序，如果用户登录的所有其他页面工作正常，但我从帐户注销的时间比在所有页面中都出错。我知道页面从cookie获取值，但如果cookie是空的，那么它会变为null＆amp;所以导致错误页面

错误：System.NullReferenceException：未将对象引用设置为对象的实例。

任何页面加载的VB代码

Dim var, Type As String
        var = Server.HtmlEncode(Request.Cookies("chkusername").Value)
        Type = Server.HtmlEncode(Request.Cookies("User_Type").Value)
        Dim LogIn, LogOut, listup As Control
        Dim BtnProfile As Button = Page.Master.FindControl("myAccount")

        LogIn = Master.FindControl("login")
        LogOut = Master.FindControl("logout")
        listup = Master.FindControl("list")

        'not login
        If HttpContext.Current.Request.Cookies("chkusername") Is Nothing Then
            listup.Visible = True
            LogIn.Visible = True
            LogOut.Visible = False
            BtnProfile.Visible = False

            'login
        Else
            LogOut.Visible = True
            BtnProfile.Visible = True
            LogIn.Visible = False
            listup.Visible = False

        End If

登录页面代码

Dim User, Pass As String
        If selectbusinesstype.SelectedValue.ToString = "0" Then
            Response.Write("<script language='javascript'>alert('Select login type first');</script>")
        ElseIf selectbusinesstype.SelectedValue = "Hospitals" Then

            Try
                If loginId.Text <> "" And password.Text <> "" Then

                    Dim str As String = "select * from hospitals where username='" + loginId.Text + "' and Password='" + password.Text + "';"
                    Dim cmd As New MySqlCommand(str, con)
                    con.Open()
                    Dim da As New MySqlDataAdapter(cmd)
                    Dim ds As New DataSet
                    da.Fill(ds)
                    con.Close()
                    User = ds.Tables(0).Rows(0)("username")
                    Pass = ds.Tables(0).Rows(0)("password")

                    If ds.Tables(0).Rows.Count > 0 Then

                        If User = loginId.Text.ToString And Pass = password.Text.ToString Then
                            Response.Cookies("User_Type").Value = "Hospitals"
                            Response.Cookies("chkusername").Value = loginId.Text
                            Response.Redirect("hospital-profile.aspx?user=" + Request.Cookies("chkusername").Value)
                        Else
                            Response.Write("<script language='javascript'>alert('User name or password is invalid');</script>")
                        End If
                    Else
                        Response.Write("<script language='javascript'>alert('User name or password is invalid');</script>")
                    End If
                Else
                    Response.Write("<script language='javascript'>alert('Enter All the Details');</script>")
                End If

            Catch ex As Exception
                Response.Write("<br /><br /><br /><br /><br />")
                Response.Write(ex)
                con.Close()
            End Try

Answer 1

你有以下行，

Dim var, Type As String
var = Server.HtmlEncode(Request.Cookies("chkusername").Value)
Type = Server.HtmlEncode(Request.Cookies("User_Type").Value)

将其转换为

Dim var, Type As String

If not HttpContext.Current.Request.Cookies("chkusername") Is Nothing Then
    var = Server.HtmlEncode(Request.Cookies("chkusername").Value)
End If

If not HttpContext.Current.Request.Cookies("User_Type") Is Nothing Then
    Type = Server.HtmlEncode(Request.Cookies("User_Type").Value)
End If

从用户帐户注销后，所有页面都显示错误

1 个答案: