Combobox Parent-Child Question

I have 3 comboboxes (ex. State, County, City). I have code in the Combobox_SelectionChangeCommitted function to load the child combobox when the Parent is selected. If there's only 1 item loaded into the child combobox, I want that to be selected automatically.

Assuming that there's only 1 County per State and 1 City per County, the expected behavior is that I select a State and the County is automatically selected since there's only 1, then the City is automatically selected since there's only 1 city for the County that was selected.

The County list is getting loaded properly when I select a State, but when it's selected, the ChangeCommitted function is not firing, which means that the City is not getting loaded.

Is there a better way of doing this? I'm fairly new to VB.NET and used to doing things in VB6.

Code:

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Private Sub cboState_SelectionChangeCommitted(ByVal sender As Object, ByVal e As System.EventArgs) Handles cboState.SelectionChangeCommitted

        cboCounty.Items.Clear()
        cboCity.Items.Clear()

        If cboState.SelectedIndex <> -1 Then
            LoadCountiesByState(cboCounty)
        End If

End Sub

Private Sub cboCounty_SelectionChangeCommitted(ByVal sender As Object, ByVal e As System.EventArgs) Handles cboCounty.SelectionChangeCommitted

        cboCity.Items.Clear()

        If cboCounty.SelectedIndex <> -1 Then
            LoadCitiesByCounty(cboCity)
        End If

End Sub

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The following functions are in a different code module and need to stay there since they are called by multiple locations within the project. Also, defaulting to the only entry needs to stay in here as well for the same reason.

Code:

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Public Sub LoadCountiesByState(ByRef cbx as ComboBox, ByVal intStateID as Integer)

    'Code to Load a list of Counties by State ID

    For Each County in ...
          cbx.Items.Add(New ListData(intCountyID, strCountyName))
    Next

    If cbx.Items.Count = 1 Then cbx.SelectedIndex = 0

End Sub

Public Sub LoadCitiesByCounty(ByRef cbx as ComboBox, ByVal intCountyID as Integer)

    'Code to Load list of Cities by County ID

    For Each City in ...
          cbx.Items.Add(New ListData(intCityID, strCityName))
    Next

    If cbx.Items.Count = 1 Then cbx.SelectedIndex = 0

End Sub

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malleyo,

I think that using the combobox's SelectedIndexChanged event, not SelectionChangeCommitted, should work.

Kerry Moorman

Or, otherwise, could you call the event manually?

Quote:

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Originally Posted by kmoorman

malleyo,

I think that using the combobox's SelectedIndexChanged event, not SelectionChangeCommitted, should work.

Kerry Moorman

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I can't use the SelectedIndexChanged event. I need the 2nd combobox to load when the first is selected. The user can press a button while focus is on the first combobox to skip to a particular letter. When that happens, the combobox drops down and the user can scroll to whichever item he/she wants. If I use the SelectedIndexChanged event, the 2nd combobox is loaded every time the user clicks the arrows to scroll through the dropped down 1st combobox. If I use the SelectionChangeCommitted event, it wait until the user has selected which item he/she wants and presses Enter. I want to limit the number of times that the 2nd combobox is loaded since it has to go to the database each time.

Quote:

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Originally Posted by javajawa

Or, otherwise, could you call the event manually?

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How do I call it manually? Can it be called from the other code module (ex LoadCountiesByState)? What happens if that particular form doesn't have a SelectionChangeCommitted event defined?

My undertanding is that

Code:

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If cbx.Items.Count = 1 Then cbx.SelectedIndex = 0

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was giving you the trouble.

what you could do is add to your old code an overload:

Code:

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Public Sub LoadCountiesByState(ByRef cbx as ComboBox, ByVal intStateID as Integer, ByRef CityBox As ComboBox)
  LoadCountiesByState(cbx, intStateID)
  LoadCitysFromCounty(CityBox, 0)
End Sub

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The the call becomes:

Code:

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Private Sub cboState_SelectionChangeCommitted(ByVal sender As Object, ByVal e As System.EventArgs) Handles cboState.SelectionChangeCommitted
        If cboState.SelectedIndex <> -1 Then
            LoadCountiesByState(cboCounty, cboState.SelectedIndex, cboCity)
        End If
End Sub

Private Sub cboCounty_SelectionChangeCommitted(ByVal sender As Object, ByVal e As System.EventArgs) Handles cboCounty.SelectionChangeCommitted
        If cboCounty.SelectedIndex <> -1 Then
            LoadCitiesByCounty(cboCity, cboCounty.SelectedIndex)
        End If
End Sub

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(I personally think the clears should go in the load functions, unless there's a perticular reason why they're not there?)

In case you're not familar with overload functions, if you put both defintions there, VB will pick the function which matches the the parameters you give it. It's best to have Option Strict On (well, it's always best to have Option Strict On :D)

I solved the problem by changing the SelectionChangeCommitted to SelectedIndexChanged and pre-loading the classes when the app starts. That way, it doesn't have to make a call to the database every time the SelectedIndex changes.

Thanks for your help and suggestions! :wave: