我对在visualstudio（最近从msaccess转换过来）中开发应用程序还是相当陌生的，我正在vb.net中编写代码。我的问题是关于如何根据对另一个组合框的选择来更改第二个组合框。我的所有结果都存储在单独的sql server数据库中。
当我的表格被调用时，以下将执行；

Public Sub New(ByVal _PartID As String)

    InitializeComponent() 'Required at the begining of calling a new form'

    LoadCombobox(cboArea, "SELECT [ID], [Name], [MRPShow] FROM [LocationArea] WHERE [MRPShow] = 1", "Name", "ID")

    cboArea.SelectedValue = 0
    cboBay.SelectedValue = 0

    LoadPartData(_PartID)

End Sub

Public Sub LoadCombobox(_cbo As ComboBox, _query As String, _displayMember As String, _valueMember As String)

    Dim SQL As New SQLControl

    _cbo.Items.Clear()

    SQL.ExecQuery(_query)

    If SQL.HasException(True) Then Exit Sub

    _cbo.DataSource = SQL.DBDT

    _cbo.DisplayMember = _displayMember
    _cbo.ValueMember = _valueMember

End Sub

Public Sub LoadPartData(_ID As String)

    Sql.AddParam("@ID", _ID)
    Sql.ExecQuery("SELECT * FROM [Part] " &
                      "WHERE ID = @ID")

    If Sql.RecordCount < 1 Then
        MsgBox("No item found.")
        Exit Sub
    End If

    For Each r As DataRow In Sql.DBDT.Rows

        txtID.Text = r("ID").ToString()
        txtMRPID.Text = r("MRP_ID").ToString()
        txtPartName.Text = r("PartName").ToString()
        txtManufacturer.Text = r("Manufacturer").ToString()
        txtManufacturerPartNo.Text = r("PartNumber").ToString()

        cboVendor1.SelectedValue = r("Vendor1")
        txtWebsiteVendor1.Text = r("Vendor1Link").ToString()
        cboVendor2.SelectedValue = r("Vendor2")
        txtWebsiteVendor2.Text = r("Vendor2Link").ToString()
        cboVendor3.SelectedValue = r("Vendor3")
        txtWebsiteVendor3.Text = r("Vendor3Link").ToString()

        cboArea.SelectedValue = r("LocationArea")
        cboBay.SelectedValue = r("LocationBay")
        cboRack.SelectedValue = r("LocationRack")

        cboPartAssembly.SelectedValue = r("PartAssembly")
        txtDrawingNo.Text = r("DrawingNumber").ToString()
        txtImagePath.Text = r("Image").ToString()

    Next

    If Not String.IsNullOrEmpty(txtWebsiteVendor3.Text) Then

        Process.Start(txtWebsiteVendor3.Text)

    End If

End Sub

我的sqlcontrol类的代码段

Imports System.Data.SqlClient

Public Class SQLControl
    Private DBCon As New SqlConnection("---HIDDEN---")
    Private DBCmd As SqlCommand

    ' DB DATA
    Public DBDA As SqlDataAdapter
    Public DBDT As DataTable

    ' QUERY PARAMETERS
    Public Params As New List(Of SqlParameter)

    ' QUERY STATISTICS
    Public RecordCount As Integer
    Public Exception As String

    Public Sub New()
    End Sub

    ' ALLOW CONNECTION STRING OVERRIDE
    Public Sub New(ConnectionString As String)
        DBCon = New SqlConnection(ConnectionString)
    End Sub

    ' EXECUTE QUERY SUB
    Public Sub ExecQuery(Query As String, Optional ReturnID As Boolean = False)
        ' RESET QUERY STATS
        RecordCount = 0
        Exception = ""

        Try
            DBCon.Open()

            ' CREATE DB COMMAND
            DBCmd = New SqlCommand(Query, DBCon)

            ' LOAD PARAMS INTO DB COMMAND
            Params.ForEach(Sub(p) DBCmd.Parameters.Add(p))

            ' CLEAR PARAM LIST
            Params.Clear()

            ' EXECUTE COMMAND & FILL DATASET
            DBDT = New DataTable
            DBDA = New SqlDataAdapter(DBCmd)
            RecordCount = DBDA.Fill(DBDT)

            If ReturnID = True Then

                Dim ReturnQuery As String = "SELECT @@IDENTITY As LastID;"
                DBCmd = New SqlCommand(ReturnQuery, DBCon)
                DBDT = New DataTable
                DBDA = New SqlDataAdapter(DBCmd)
                RecordCount = DBDA.Fill(DBDT)

            End If

        Catch ex As Exception
            ' CAPTURE ERROR
            Exception = "ExecQuery Error: " & vbNewLine & ex.Message
        Finally
            ' CLOSE CONNECTION
            If DBCon.State = ConnectionState.Open Then DBCon.Close()
        End Try
    End Sub

    ' ADD PARAMETERS
    Public Sub AddParam(Name As String, Value As Object)
        Dim NewParam As New SqlParameter(Name, Value)
        Params.Add(NewParam)
    End Sub

    ' ERROR CHECKING
    Public Function HasException(Optional Report As Boolean = False) As Boolean
        If String.IsNullOrEmpty(Exception) Then Return False
        If Report = True Then MsgBox(Exception, MsgBoxStyle.Critical, "Exception:")
        Return True
    End Function
End Class

因此，我希望实现的是当[cboarea]值更改时，下一个组合框[cbobay]将更新为以下内容：；

Private Sub cboArea_SelectedIndexChanged(sender As Object, e As EventArgs) Handles cboArea.SelectedIndexChanged

    cboBay.SelectedValue = 0

    Try

        SQL.AddParam("@SelectedValueOfcboArea", cboArea.SelectedValue)
        SQL.ExecQuery("SELECT [ID], [Name], [LocationAreaID] FROM [LocationBay] WHERE [LocationAreaID] = @SelectedValueOfcboArea")

        If SQL.HasException(True) Then Exit Sub

        cboBay.DataSource = SQL.DBDT

        cboBay.DisplayMember = "Name"
        cboBay.ValueMember = "ID"

    Catch ex As Exception

    End Try

End Sub

上面的内容似乎工作正常，但是当我第一次打开带有特定partid的表单时，我收到以下错误消息；


我相信这些都是初始化代码的错误，在初始化代码中，部件数据被加载到每个控件中，因此调用onvaluechanged事件，该事件不断抛出异常错误，但是我正在努力确定如何解决这个问题，因为我说的是，在加载表单和用户执行操作之后，代码工作正常。
关于另一个问题，我在这里所做的关于从sql数据库收集数据的工作是最好的方法吗？我知道大多数人都遵循这个原则，但我也一直在研究数据集并将其绑定到控件，但我没有看到一篇文章说明什么样的实现方式更好/更快？