WPF distinguish between coding-SelectionChanged and the mouse-SelectionChanged.

Question

Hi everyone! I have a machiavellian question (for me). In my WPF application I have a ListBox that has in the ItemTemplate a Combobox. When the user select a ComboBoxItem, I have to do some complex operations on the ObservableCollection that is the ItemsSource of the ListBox, then I have to show the ListBox with the changed data. The problem is that if I handle the event "SelectionChanged" of the ComboBox control, every time I modify the source-class of the comboboxItems I enter in the method that handle the event, and this generate wrong results. In short I have to distinguish, in some way, between the SelectionChanged generated by code, and the SelectionChanged generated manually by the user with the mouse. I have tried many ways, but nothing that works :-(

The soution I thought was the best, is to handle the event "GotFocus" or "MouseUp" of the ContentPresenter of the ItemContainerStyle of the Combo, or else to handle the same events ("GotFocus" and "MouseUp") of the ItemsPanel of the Combo, but the method I handled didn't capture the event (in debug the cursor doesn't enter at all in the method).

I can't use a boolean to stop the method "SelectionChanged" until the "first round" is finished, because the changes of the source-class of the ComboBoxItems occurs after that the method has been all executed.

The default value of the Combos is not always the first (it would be too easy :-)), and not always the same. Everytime the user select an item of one of the Combo, the default value of the other Combos has to change.

Can you help me? Pileggi

' XAML
<Style x:Key="modComboCriteriEventParts" TargetType="{x:Type ComboBox}">
    <EventSetter Event="Selector.SelectionChanged" Handler="cb_SelectionChanged"/>
</Style>

<DataTemplate x:Key="modLBoxCriteriParts">
    <ComboBox Style = "{StaticResource modComboCriteriEventParts}"
        ItemsSource = "{Binding CriteriItemList}"
        ItemContainerStyle = "{DynamicResource modComboContainerParts}"
        SelectedIndex = "{Binding valueSelected}" ... />
</DataTemplate>

<ListBox x:Name="lbCriteri" IsSynchronizedWithCurrentItem="True"
    ItemsSource = "{Binding CriteriList, Source={StaticResource P_CriteriDataSource}}"
    ItemTemplate = "{DynamicResource modLBoxCriteriParts}"
    ... />


' Code Behind
Private Sub cb_SelectionChanged(ByVal sender As System.Object, ByVal e As SelectionChangedEventArgs)
    Dim ri as New RicambiCriteriList() As ObservableCollection(Of P_CriteriItem)

    ' some complex operations with ri ...

    be = BindingOperations.GetBindingExpression(Me.lbCriteri, ListBox.ItemsSourceProperty)
    Dim allCriteri As P_Criteri = DirectCast(be.DataItem, P_Criteri)
    allCriteri.AddData (ri)

    e.Handled = True
End Sub


' Source-Class
Public Class P_Criteri

    Private _CriteriList As New ObservableCollection(Of P_CriteriItem)

    Public ReadOnly Property CriteriList() As ObservableCollection(Of P_CriteriItem)
        Get
            CriteriList = _CriteriList
        End Get
    End Property

    Public Sub AddData(ByVal CriteriListPass As ObservableCollection(Of P_CriteriItem))
        _CriteriList.Clear()
        For Each a As P_CriteriItem In CriteriListPass
            _CriteriList.Add(a)
        Next
    End Sub
End Class

Public Class P_CriteriItem
    Implements INotifyPropertyChanged

    Public Sub New(ByVal criterioPass As String, ByVal CriteriItemListPass As ObservableCollection(Of P_CriteriItemValore), _
        ByVal widthCriteriValuesPass As Double)

        Me._criterio = criterioPass
        Me._CriteriItemList = CriteriItemListPass
        Me._widthCriteriValues = widthCriteriValuesPass
    End Sub

    Private _criterio As String = ""
    Private _CriteriItemList As New ObservableCollection(Of P_CriteriItemValore)

    Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged

    Public Property criterio() As String
        Get
            Return Me._criterio
        End Get
        Set(ByVal value As String)
            If Not Object.Equals(Me._criterio, value) Then
                Me._criterio = value
                Me.OnPropertyChanged ("criterio")
            End If
        End Set
    End Property

    Public Property CriteriItemList() As ObservableCollection(Of P_CriteriItemValore)
        Get
            Return Me._CriteriItemList
        End Get
        Set(ByVal value As ObservableCollection(Of P_CriteriItemValore))
            If Not Object.Equals(Me._CriteriItemList, value) Then
                Me._CriteriItemList = value
                Me.OnPropertyChanged ("CriteriItemList")
            End If
        End Set
    End Property

    Protected Overridable Sub OnPropertyChanged(ByVal propertyName As String)
        Dim handler As PropertyChangedEventHandler = Me.PropertyChangedEvent
        If handler IsNot Nothing Then
            RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(propertyName))
        End If
    End Sub
End Class

Public Class P_CriteriItemValore
    Implements INotifyPropertyChanged

    Public Sub New(ByVal criterioValorePass As String)
        Me._criterioValore = criterioValorePass
    End Sub

    Private _criterioValore As String = Nothing

    Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged

    Public Property criterioValore() As String
        Get
            Return Me._criterioValore
        End Get
        Set(ByVal value As String)
            If Not Object.Equals(Me._criterioValore, value) Then
                Me._criterioValore = value
                Me.OnPropertyChanged ("criterioValore")
            End If
        End Set
    End Property

    Protected Overridable Sub OnPropertyChanged(ByVal propertyName As String)
        Dim handler As PropertyChangedEventHandler = Me.PropertyChangedEvent
        If handler IsNot Nothing Then
            RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(propertyName))
        End If
    End Sub
End Class

Answer 1

Firstly I think its better to handle events on the item container itself and not on the content presenter within the item. And now that I think of it that's probably why you don't see the events. The container is probably eating the events for selection.

But either way if you can't catch the MouseDown/GotFocus events, you can use the PreviewMouseDown/PreviewGotFocus events. Just in case you are not sure what these mean you should read up on wpf event routing architecture and bubbling and tunneling events.