populate combobox from the selected item of other combobox - vb.net

Question

I'm creating a form in which a user has to give a State name and a City name. Where the city depends on the state.
Code for populating the city:
Dim ds As DataSet = New DataSet
Dim adapter As New OleDb.OleDbDataAdapter
Dim sql As String
sql = "SELECT * from statestab order by `state` ASC;"
adapter.SelectCommand = New OleDb.OleDbCommand(sql, con)
adapter.Fill(ds)
ComboBoxstate.DataSource = ds.Tables(0)
ComboBoxstate.ValueMember = "stateid"
ComboBoxstate.DisplayMember = "state"
Code for the city :
Dim ds As DataSet = New DataSet
Dim adapter As New OleDb.OleDbDataAdapter
Dim sql As String
Dim st As Integer
st = ComboBoxstate.SelectedValue.ToString()
sql = "SELECT * from citytab where stateid=st order by `cityname` ASC;"
adapter.SelectCommand = New OleDb.OleDbCommand(sql, con)
adapter.Fill(ds)
citycombo.DataSource = ds.Tables(0)
citycombo.ValueMember = "cityid"
citycombo.DisplayMember = "cityname"
In the combobox, when the selected city is changed, I call the city load function to populate the city combobox.
But I'm cant populate the city combobox.

Answer 1

You will need handler in Selected_Index_Changed in your State Combobox. From there call your routine to load up the City, in the SQL for city you would need to do
where stateid=" & comboBox1.SelectedValue.ToString()

Answer 2

Here is full text, Note that is can be much better but I tried to keep your syntax in tact:
Private Sub cboState_SelectedIndexChanged(sender As Object, e As EventArgs) Handles cboState.SelectedIndexChanged
Load_Cities()
End Sub
Private Sub Load_States()
Dim ds As DataSet = New DataSet
Dim adapter As New OleDb.OleDbDataAdapter
Dim sql As String
sql = "SELECT * from tblState order by StateName ASC;"
adapter.SelectCommand = New OleDb.OleDbCommand(sql, con)
adapter.Fill(ds)
cboState.DataSource = ds.Tables(0)
cboState.ValueMember = "stateid"
cboState.DisplayMember = "statename"
End Sub
Private Sub Load_Cities()
On Error Resume Next
Dim ds As DataSet = New DataSet
Dim adapter As New OleDb.OleDbDataAdapter
Dim sql As String
sql = "SELECT * from tblCity where StateID = " & cboState.SelectedValue.ToString() & " order by CityName ASC;"
adapter.SelectCommand = New OleDb.OleDbCommand(sql, con)
adapter.Fill(ds)
cboCity.DataSource = ds.Tables(0)
cboCity.ValueMember = "CityID"
cboCity.DisplayMember = "CityName"
End Sub