主题：[分享]限制用户用同一个账户只能登陆1个客户端

Dim UserName As String = e.Form.Controls("UserName").Value

Dim cmd As New SQLCommand

Dim dt As DataTable

Dim dr1 As DataRow

cmd.C

If UserName = ""  Then

    Messagebox.show("请选择用户!","提示",MessageBoxButtons.OK,MessageBoxIcon.Information)

    Return

End If

Cmd.CommandText = "Select * From {Users} Where [Name] = '" & UserName & "'"

If cmd.ExecuteScalar() = 0 Then

    Dim Result As DialogResult

    Result = MessageBox.Show("您输入的用户名或者密码错误,请重新输入!", "提示", MessageBoxButtons.OK,MessageBoxIcon.Information)

    Return

End If

cmd.CommandText = "Select * From {Users} Where [Name] = '" & UserName & "'"

dt = cmd.ExecuteReader

dr1 = dt.DataRows(0)

If e.Form.Controls("PassWord").Value = dr1("Password") Then

    If dt.DataRows.Count = 1 Then

        Dim d1 As Date = dt.DataRows(0)("最近在线")

        Dim d2 As Date = Date.now()

        Dim t As TimeSpan = d2 - d1

        If t.TotalSeconds >= 30 Then ‘ 30是秒数，就是用户在30秒没有报道的话，会被系统认为退出，计划管理是10秒执行一次，具体自己修改即可

            _UserName = UserName

            _UserGroup = dr1("Group")

            Dim s As String = e.Form.Controls("UserName").Value '这段代码是用来保存用户名的

            FileSys.WriteAllText("c:\UserName.txt", s, False, Encoding.Default)

            e.Form.Close

        Else

            MessageBox.Show("此用户已登录!","提示",MessageBoxButtons.OK)

        End If

    End If

Else

    Messagebox.show("您输入的用户名或者密码错误,请重新输入!","提示",MessageBoxButtons.OK,MessageBoxIcon.Information)

End If