Visual Basic

Private ComboBox1LoadTime As Boolean<br />
 Dim ds, ds1 As New DataSet

<br />
now fill the combo box as following at load event of form <br />
<br />
Dim str As String<br />
<br />
        Dim mdins As New mdGlobal 'here mdglobal is <br />
        str = "select areaname,areaid from areainfo"<br />
        ds = New DataSet<br />
        ComboBox1LoadTime = True<br />
        ds = mdins.GetResultFromQuery(str)<br />
'in above statement i use class mdglobal which is created by me. and GetResultFromQuery return dataset<br />
<br />
        ComboBox1.DataSource = ds.Tables(0)<br />
        ComboBox1.DisplayMember = "AreaName"<br />
        ComboBox1.ValueMember = "Areaid"<br />
        ComboBox1LoadTime = False<br />
        ComboBox1.SelectedIndex = -1

Private Sub ComboBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ComboBox1.SelectedIndexChanged<br />
        If Not ComboBox1LoadTime And ComboBox1.Text.Trim <> "" Then<br />
            Dim str As String<br />
            Dim mdins As New mdGlobal<br />
<br />
            ComboBox2.DataSource = Nothing<br />
            If Not ds1 Is Nothing Then<br />
                ds1.Dispose()<br />
            End If<br />
<br />
            str = "select iteminfo.itemid,itemname,area_item.areaid from iteminfo,area_item where iteminfo.itemid=area_item.itemid and area_item.areaid=" & ComboBox1.SelectedValue<br />
            ds1 = New DataSet<br />
            ds1 = mdins.GetResultFromQuery(str)<br />
<br />
            ComboBox2.DataSource = ds1.Tables(0)<br />
            ComboBox2.DisplayMember = "itemName"<br />
            ComboBox2.ValueMember = "itemid"<br />
        End If<br />
    End Sub