VB.NET 错误："The ConnectionString property has not been initialized."

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"(>>> 错误发生在这行代码上。

如果 tab 索引被更改，则也会调用子 TabSelect((。另一件事是程序会检查星期几并正确显示与该日期对应的选项卡。周一这段代码工作正常，周二一到这个错误就出现了。

Answer 1

尝试将 conn 作为参数传递到 TabSelect(( 函数中。 TabSelect(ByRef OleDbConnection conn) 这可能是范围问题，因为您正在使用全局变量