Odd my old program which has the layout made in scene builder containing a combobox , definitely has mouseclicked as an event (but it doesn't show up in the designer > generate members list) just the two you mentioned.
An extract of the code I use
B4X:
Private textBox1,recCount As TextField
Private selectButton,fromButton,whatButton,goButton As Button
Private choiceBox As ComboBox
Private fromWhere As String
Private whichSelect As Int
Then further down I use
B4X:
Sub choiceBox_MouseClicked (EventData As MouseEvent)
If choiceBox.SelectedIndex <> -1 Then
whatButton.RequestFocus
choiceBox.Enabled = False
Select whichSelect
Case 1:
fromWhere = choiceBox.Items.Get(choiceBox.SelectedIndex)
Case 2:
Dim tmp As String
tmp = choiceBox.Items.Get(choiceBox.SelectedIndex)
I checked the layout again and it reports the control as a ComboBox.