populating combo box on run time - vb.net

Question

I got two combo box on the system a Category and Sub Category
my concept must be when i choose COM OR PRT on cmbCategory,
cmbSubCategory will automatically display the corresponding subcategory for the category chosen
Private Sub cmbCategory_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmbCategory.SelectedIndexChanged
If cmbCategory.Text = "COM" Then
cmbSubCategory.Items = "SU, MON"
End If
End Sub
my code returns error
Property Items is Read Only

Answer 1

Items is a collection so to put things into it you need to add them to the collection rather than direct assignment.
If SU and MON are meant to appear as separate items in the combo box then you could do something similar to:
Private Sub cmbCategory_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmbCategory.SelectedIndexChanged
If cmbCategory.Text = "COM" Then
cmbSubCategory.Items.Clear()
cmbSubCategory.Items.Add("SU")
cmbSubCategory.Items.Add("MON")
End If
End Sub
If SU, MON is meant to appear as a single item then you could do:
Private Sub cmbCategory_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmbCategory.SelectedIndexChanged
If cmbCategory.Text = "COM" Then
cmbSubCategory.Items.Clear()
cmbSubCategory.Items.Add("SU, MON")
End If
End Sub
Note that we use Clear to remove items from the combo box/ensure it is empty before populating it with the right options.
PS. I noticed that one of the tags for this question is "SQL", but from what I've read I don't think that this question has a SQL component to it...