VB.NET错误：“ConnectionString属性尚未初始化。”

Question

Dim Current As String
Current = Directory.GetCurrentDirectory()
con.ConnectionString = "PROVIDER = Microsoft.Jet.OLEDB.4.0;Data Source = " & Current & "\SchoolMaticsDatabase.mdb"
con.Open()
TabSelect()
con.Close()

Private Sub TabSelect()
        Select Case TabControl1.SelectedIndex
            Case Is = 0
                TabDay = "Monday"
            Case Is = 1
                TabDay = "Tuesday"
            Case Is = 2
                TabDay = "Wednesday"
            Case Is = 3
                TabDay = "Thursday"
            Case Is = 4
                TabDay = "Friday"
            Case Is = 5
                TabDay = "Saturday"
            Case Is = 6
                TabDay = "Sunday"
        End Select
        ds.Clear()
        sql = "SELECT [Forename],[Surname],[Subject Speciality 1],[Subject Speciality 2],[Subject Speciality 3],[Subject Speciality 4],[Subject Speciality 5],[Subject Speciality 6]," & StartTime & "," & EndTime & ",[Spec1],[Spec2],[Spec3],[Spec4],[Spec5],[Spec6] FROM [Staff] WHERE " & TabDay & " LIKE 'T'"
        da = New OleDb.OleDbDataAdapter(sql, con)
        da.Fill(ds, "SchoolMaticsDatabase")
End Sub

da.fill(ds，"SchoolMaticsDatabase")>>>错误发生在这一行代码上.

如果选项卡索引被更改，子TabSelect()也会被调用。另一件事是程序检查一周中的某一天，并正确地显示与这一天对应的选项卡。周一，这段代码正常工作，一碰到星期二就会出现这个错误。

Answer 1

尝试将conn作为参数传递到TabSelect()函数中。TabSelect(ByRef OleDbConnection conn)，这可能是一个范围问题，因为您正在处理全局变量。