VB Net - How to get cascading drop down list to select self insert row without error? - vb.net

Question

I have 4 dropdownlist in my web form that is cascading, the value of the 1st dropdownlist will affect the selection of the 2nd dropdownlist and so on.
Protected Sub line_selectedindexchanged(ByVal sender As Object, ByVal e As EventArgs)
Dim level1_ID As Integer = Convert.ToInt32(line.SelectedValue.ToString())
FillProcess(level1_ID)
End Sub
Protected Sub ddlprocess_selectedindexchanged(ByVal sender As Object, ByVal e As EventArgs)
Dim level2_ID As Integer = Convert.ToInt32(ddlprocess.SelectedValue.ToString())
FillEquipment(level2_ID)
End Sub
Protected Sub equipment_selectedindexchanged(ByVal sender As Object, ByVal e As EventArgs)
Dim level3_ID As Integer = Convert.ToInt32(equipment.SelectedValue.ToString())
FillStep(level3_ID)
End Sub
Private Sub FillLine() '1st dropdown
Dim dt As New DataTable
Dim strSql = "select distinct level1_id, [LCODE1]+ ' | '+[LNAME1] as [LCODE1]" _
& " FROM [SQLIOT].[dbo].[ZVIEW_MCM_LEVEL_LOOKUP]"
Using conn As New SqlConnection(ConStr),
cmd As New SqlCommand(strSql, conn)
conn.Open()
dt.Load(cmd.ExecuteReader)
End Using
If dt.Rows.Count > 0 Then
line.DataSource = dt
line.DataTextField = "LCODE1"
line.DataValueField = "level1_id"
line.DataBind()
line.Items.Insert(0, "")
End If
End Sub
Private Sub FillProcess(ByVal level1_ID As Integer) '2nd dropdown
Dim dt As New DataTable
Dim strSql = "select distinct level2_id, [LCODE2]+ ' | '+[LNAME2] as [LCODE2] " _
& "FROM [SQLIOT].[dbo].[ZVIEW_MCM_LEVEL_LOOKUP] where level1_id = #level1_id"
Using conn As New SqlConnection(ConStr),
cmd As New SqlCommand(strSql, conn)
cmd.Parameters.Add("#level1_id", SqlDbType.Int).Value = level1_ID
conn.Open()
dt.Load(cmd.ExecuteReader)
End Using
If dt.Rows.Count > 0 Then
ddlprocess.DataSource = dt
ddlprocess.DataTextField = "LCODE2"
ddlprocess.DataValueField = "level2_id"
ddlprocess.DataBind()
ddlprocess.Items.Insert(0, "")
End If
End Sub
Private Sub FillEquipment(ByVal level2_ID As Integer) '3rd dropdown
Dim dt As New DataTable
Dim strSql = "select distinct level3_id, [LCODE3]+ ' | '+[LNAME3] as [LCODE3] " _
& "FROM [SQLIOT].[dbo].[ZVIEW_MCM_LEVEL_LOOKUP] where level2_id = #level2_id"
Using conn As New SqlConnection(ConStr),
cmd As New SqlCommand(strSql, conn)
cmd.Parameters.Add("#level2_id", SqlDbType.Int).Value = level2_ID
conn.Open()
dt.Load(cmd.ExecuteReader)
End Using
If dt.Rows.Count > 0 Then
equipment.DataSource = dt
equipment.DataTextField = "LCODE3"
equipment.DataValueField = "level3_id"
equipment.DataBind()
equipment.Items.Insert(0, "")
End If
End Sub
Private Sub FillStep(ByVal level3_ID As Integer) '4th dropdown
Dim dt As New DataTable
Dim strSql = "select distinct [LCODE4]+ ' | '+[LNAME4] as [LCODE4] " _
& "FROM [SQLIOT].[dbo].[ZVIEW_MCM_LEVEL_LOOKUP] where level3_id = #level3_id"
Using conn As New SqlConnection(ConStr),
cmd As New SqlCommand(strSql, conn)
cmd.Parameters.Add("#level3_id", SqlDbType.Int).Value = level3_ID
conn.Open()
dt.Load(cmd.ExecuteReader)
End Using
If dt.Rows.Count > 0 Then
[step].DataSource = dt
[step].DataTextField = "LCODE4"
[step].DataBind()
[step].Items.Insert(0, "")
End If
End Sub
The reason I want a blank 1st row is so that when the form loads I want all dropdownlist to start off empty. During testing I thought to try selecting back to blank 1st row after selecting a value. This causes an error to occur at:
'Any one of the selectedindexchanged sub depending on which list I used
Protected Sub line_selectedindexchanged(ByVal sender As Object, ByVal e As EventArgs)
Dim level1_ID As Integer = Convert.ToInt32(line.SelectedValue.ToString()) '--> issue here
FillProcess(level1_ID)
End Sub
Error message being:
Input string was not in a correct format.
Anything I can do to fix this?