Question

好的，所以我有一个名为quote_guidelines的表单，我想使用一个过程来更新我的数据库，并在quote_guidelines表单中输入值。价值观是装饰，食品/饮料和娱乐的描述和成本。已为每个选项卡分配了其中一个附加服务。我想创建一个用这些新值更新数据库的过程。问题是查询必须包含不同的表和不同的文本框名称。我试图通过在变量中保存表和文本框的名称来解决这个问题，然后将其传递给过程。

表变量在sql语句中工作正常但是，文本框名称不行。我试过这个：

quote_guidelines.Controls(description_textbox).Text

但这不起作用。

这是我的问题：

query = "UPDATE " & additional & " SET description='" & quote_guidelines.Controls("" & description_textbox & "").Text & "', cost= " & quote_guidelines.Controls("" & cost_textbox & "").Text & " WHERE " & additional & "ID='" & y & "'"

当我运行程序时，我收到以下错误“EHCC_BookingSystem.exe中发生了'System.NullReferenceException'类型未处理的异常

附加信息：对象引用未设置为对象的实例。“

我刚刚意识到这可能是我犯过的其他一些愚蠢的错误，所以这就是整个程序：

Sub UpdateAdditionals(textbox3 As System.Object, textbox4 As System.Object, textbox5 As System.Object, textbox6 As System.Object, textbox7 As System.Object, textbox8 As System.Object, ByRef additional As String, ByRef description_textbox As String, ByRef cost_textbox As String)
    mysqlconn = New MySqlConnection
    mysqlconn.ConnectionString = "Server=localhost;userid=root;password=root;database=comp4"
    Dim reader As MySqlDataReader
    MsgBox(additional & description_textbox & cost_textbox)
    Try
        mysqlconn.Open()
        Dim query As String
        query = "UPDATE " & additional & " SET description='" & quote_guidelines.Controls.Find(description_textbox, True).FirstOfDefault().Text & "', cost= " & quote_guidelines.Controls.Find(cost_textbox, True).FirstOfDefault().Text & " WHERE " & additional & "ID='" & y & "'"
        MsgBox(query)
        command = New MySqlCommand(query, mysqlconn)
        reader = command.ExecuteReader()
        mysqlconn.Close()
    Catch ex As MySqlException
        MessageBox.Show(ex.Message)
    Finally
        mysqlconn.Dispose()
    End Try

End Sub

Answer 1

试试这个 - 在Controls中替换Controls.Find（注意`True参数来搜索控件子项）：

query = "UPDATE " & additional & " SET description='" & TryCast(quote_guidelines.Controls.Find(description_textbox, True)(0), TextBox).Text & "', cost= " & TryCast(quote_guidelines.Controls.Find(cost_textbox, True)(0).Text & " WHERE " & additional & "ID='" & y & "'"

另请注意，您可以.FirstOfDefault()获取第一个控件（不要忘记施放）：

Controls.Find("nameofcontrol", True).FirstOfDefault()

VB.NET在文本框名称中使用变量

1 个答案: