Question

所以我有三个带有文本框的表单，我将它们保存到db的最后一个，一个非常庞大且迭代，所以我想写一个循环。但是当我试图循环它们时，它似乎并没有从其他形式中获取它们，我做错了什么？

 For i = 1 To 12
            Dim txtbox_bem As TextBox = CType(frm_new_prot_2.Controls("frm_new_prot_2.txtbox_bem1_" & i), TextBox)
            Dim txtbox_soll As TextBox = CType(frm_new_prot_2.Controls("txtbox_soll1_" & i), TextBox)
            Dim txtbox_messw As TextBox = CType(frm_new_prot_2.Controls("txtbox_messw1_" & i), TextBox)
            Dim txtbox_einheit As TextBox = CType(Controls("frm_new_prot_2.txtbox_einheit1_" & i), TextBox)
            Dim txtbox_max As TextBox = CType(Controls("frm_new_prot_2.txtbox_max1_" & i), TextBox)
            Dim txtbox_min As TextBox = CType(Controls("frm_new_prot_2.txtbox_min1_" & i), TextBox)
            Dim txtbox_tol As TextBox = CType(Controls("frm_new_prot_2.txtbox_tol1_" & i), TextBox)
            Dim ckbox_ok As CheckBox = CType(Controls("frm_new_prot_2.ckbox_ok1_" & i), CheckBox)

            command.CommandText = "INSERT INTO tb_1_" & i & " (Auftraggeber, Protokollnr, 1_" & i & "bem, 1_" & i & "soll, 1_" & i & "messw, 1_" & i & "einheit, 1_" & i & "max, 1_" & i & "min, 1_" & i & "tol, 1_" & i & "ok) VALUES ('" & Auftraggeber & "'," & Protokollnr & ",'" & txtbox_bem.Text & "','" & txtbox_soll.Text & "','" & txtbox_messw.Text & "','" & txtbox_einheit.Text & "','" & txtbox_max.Text & "','" & txtbox_min.Text & "','" & txtbox_tol.Text & "','" & ckbox_ok.Text & "')"
            command.CommandType = CommandType.Text
            command.ExecuteNonQuery()
            MsgBox("success row " & i)
        Next

如你所见，我尝试了不同的组合。我得到的错误是：

“System.NullReferenceException：'对象引用未设置为对象的实例。' txtbox_bem没什么。“

Answer 1

该行......

Dim txtbox_bem As TextBox = CType(frm_new_prot_2.Controls("txtbox_bem1_.txtbox_bem1_" & i), TextBox)

正在frm_new_prot_2的控件中搜索名为"frm_new_prot_2.txtbox_bem1_" & i的控件。

那不存在。在控件集合中，只包含名称为"txtbox_bem1_" & i的文本框，因此更正的版本应为

Dim txtbox_bem As TextBox = CType(frm_new_prot_2.Controls("txtbox_bem1_" & i), TextBox)

代码中的其他行可能也不会起作用。他们应该是......

Dim txtbox_bem As TextBox = CType(frm_new_prot_2.Controls("txtbox_bem1_" & i), TextBox)
Dim txtbox_soll As TextBox = CType(frm_new_prot_2.Controls("txtbox_soll1_" & i), TextBox)
Dim txtbox_messw As TextBox = CType(frm_new_prot_2.Controls("txtbox_messw1_" & i), TextBox)
Dim txtbox_einheit As TextBox = CType(frm_new_prot_2.Controls("txtbox_einheit1_" & i), TextBox)
Dim txtbox_max As TextBox = CType(frm_new_prot_2.Controls("txtbox_max1_" & i), TextBox)
Dim txtbox_min As TextBox = CType(frm_new_prot_2.Controls("txtbox_min1_" & i), TextBox)
Dim txtbox_tol As TextBox = CType(frm_new_prot_2.Controls("txtbox_tol1_" & i), TextBox)
Dim ckbox_ok As CheckBox = CType(frm_new_prot_2.Controls("ckbox_ok1_" & i), CheckBox)

我认为你对引用如何工作有点困惑。： - ）

此外，我怀疑textboxes中的数据是您存储数据的唯一地方。这不是一个非常好的编程实践。例如......

比如说，数据来自外部设备，你有代码从设备读取数据并将其存储在textboxes中。这不好。任何人都可能意外覆盖textbox中的数据。

将数据存储在类对象的Lists或Lists中要好得多。并使用数据填充textboxes。在数据库中存储数据时，请使用lists而不是textboxes中的数据。

永远不应该使用用户界面来存储数据。希望这有帮助

Answer 2

如果不进行全部投射，调试可能会更容易。

Public Class Form2
    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        Dim lst As New List(Of String)
        For i As Integer = 1 To 3
            Dim str1 As String = Form1.Controls("TextBox" & i).Text
            lst.Add(str1)
        Next
        For Each s As String In lst
            Debug.Print(s)
        Next
    End Sub
End Class

我刚刚添加了List用于测试目的。

如何循环其他表单上的项目？

2 个答案: