如何通过 SQL Server 填充基于另一个 ComboBox 的 ComboBox？ [复制]

Question

我希望能够通过 SQL Server 上的连接字符串拥有两个组合框，其中一个是第二个的父级或所有者。这意味着每当我在第一个ComboBox 中选择一个值时，第二个ComboBox 将过滤它的结果以显示与第一个ComboBox 相关的相应值。如果您在下面看到我的代码，我会收到一条错误消息：

错误 1 ​​方法 'Private Sub cboClient_SelectedIndexChanged(sender As Object, e As System.EventArgs, EnvName As String)' 无法处理事件 'Public Event SelectedIndexChanged(sender As Object, e As System.EventArgs)' 因为它们没有兼容的签名。

目标：

1. 更改数据库连接
2. 从正确的数据库中查询正确的用户数据
3. 用该用户数据填充用户组合框

我的代码：

 Private Sub cboClient_SelectedIndexChanged(sender As Object, e As EventArgs, ByVal EnvName As String) Handles cboClient.SelectedIndexChanged
        Using con2 As New SqlConnection(ConfigurationManager.ConnectionStrings("conStr").ConnectionString)
            'Getting connection string from the specific client
            Dim cmd2 As New SqlCommand("Select * from tblCONNECTIONS where EnvName = '" & "@EnvName" & "'", con2)
            con2.Open()
            Dim dt As New DataTable
            dt.Load(cmd2.ExecuteReader())
            cmd2.Parameters.Add("@EnvName", SqlDbType.VarChar)
            cmd2.Parameters("@EnvName").Value = EnvName
            If dt.Rows.Count > 0 Then
                Dim clientConString As String = dt(0)("ConnectionString")
                'Getting the yalusers info from client specific database\
                Using con3 As New SqlConnection(clientConString)
                    cmd2 = New SqlCommand("Select * from yalusers", con3)
                    con3.Open()
                    dt.Load(cmd2.ExecuteReader())
                    cboUser.DataSource = dt
                    cboUser.DisplayMember = "First_Name"
                    cboUser.ValueMember = "ID"
                    con3.Close()
                End Using

            Else
                'Show error message : missing connection string in the YALCONNECTIONS table  
            End If

            con2.Close()
        End Using
    End Sub

如何解决这个问题？

更新：当我运行应用程序时，我在第一个组合框中有 6 个项目，而无论我选择哪一个，它都不会填充到第二个组合框中。为什么？？

Answer 1

您不能将参数添加到事件处理程序。它必须有这个定义：

Private Sub cboClient_SelectedIndexChanged(sender As Object, e As EventArgs) Handles cboClient.SelectedIndexChanged
    DoSelectedIndexChanged(sender, e, something)
End Sub

创建一个单独的子例程来完成您需要的工作，但不要让它处理事件。

Private Sub DoSelectedIndexChanged(sender As Object, e As EventArgs, ByVal EnvName As String) Handles cboClient.SelectedIndexChanged