从组合框1中选择的值填充组合框2

Question

第一个组合框具有学生管理员号码。当选择一个数字时，下一个组合框应该显示该学生的班级列表。但是，当选择一个值时，第二个组合框不显示任何内容。

AdminNo存储在数据库中的两个学生和ClassEnrollment表所示。

Imports System.Data.OleDb 

Public Class AddReport 
    Dim cn As New OleDbConnection("provider=microsoft.jet.oledb.4.0;data source=C:\ProjectDatabase.mdb") 
    Dim daa As New OleDbDataAdapter() 
    Dim dt As New DataTable() 

Private Sub btnReturn_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnReturn.Click 
    Me.Close() 
    Startup.Show() 
End Sub 

Private Sub AddReport_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load 
    StudentNameAdd() 
End Sub 

Sub StudentNameAdd() 
    cn.Open() 
    daa.SelectCommand = New OleDbCommand("Select AdminNo from Student", cn) 
    daa.Fill(dt) 
    CBStudent.Items.Clear() 
    Dim r As DataRow 
    For Each r In dt.Rows 
     CBStudent.Items.Add(r(0).ToString) 
    Next 
    cn.Close() 

End Sub 

Private Sub CBStudent_SelectedIndexChanged(sender As Object, e As EventArgs) Handles CBStudent.SelectedIndexChanged 
    dt.Reset() 
    Dim StudentAdminNo As Integer = CBStudent.SelectedValue 
    cn.Open() 
    daa.SelectCommand = New OleDbCommand("Select ClassCode from ClassEnrollment Where AdminNo=" & StudentAdminNo, cn) 
    daa.Fill(dt) 
    CBClass.Items.Clear() 
    Dim r As DataRow 
    For Each r In dt.Rows 
     CBClass.Items.Add(r(0).ToString) 
    Next 
    cn.Close() 
End Sub 

任何帮助推动我在正确的方向将不胜感激。

Answer 1

通过将Combobox的DataSource属性设置为DataTable，将DataTable绑定到ComboBox怎么样？

编辑：我测试你的代码，如果你改变

Dim StudentAdminNo As Integer = CBStudent.SelectedValue 

到

Dim StudentAdminNo As Integer = CBStudent.SelectedItem