UpdateSourceTrigger PropertyChanged on IsChecked Isn't Firing on ItemsSource of ListBox of Checkboxes

Question

I have a listbox in which the item source contains a List(of T) that has a SelectedFlag boolean property. My viewmodel is set as the DataContext of my user control and everything is working as expected except I can't get the property change even when a check box is changed.

Here is my xaml ListBox

<ListBox x:Name="lstRole" ItemsSource="{Binding Path=FAccountFunctions, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" SelectedValuePath="Id">
                <ListBox.ItemTemplate>
                    <DataTemplate>
                        <StackPanel Orientation="Horizontal">
                            <CheckBox IsChecked="{Binding Path=SelectedFlag, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" VerticalAlignment="Center" />
                            <TextBlock Text="{Binding Path=FunctionDesc}" VerticalAlignment="Center" />
                        </StackPanel>
                    </DataTemplate>
                </ListBox.ItemTemplate>
            </ListBox>

I need to call my Filter() function after a check box is checked and I normally would set the UpdateSourcTrigger=PropertyChanged to make this work.

Public Property FAccountFunctions As List(Of FunctionType)
        Get
            Return _faccountFunctions
        End Get
        Set(ByVal value As List(Of FunctionType))
            _faccountFunctions = value
            Filter()
        End Set
    End Property

The PropertyChangedEvent is getting raised on the 'SelectedFlag' property in the FAccountFunctions collection. How can I raise an event on the items source when one of the properties SelectedFlag changes?

Changed my FAccountFunctions property to an ObservableCollection...no luck.

Answer 1

You'll need to make your Collection's CollectionChanged event fire when your Item's PropertyChanged event fires.

Something like:

MyCollection.CollectionChanged += MyCollectionChanged;

...

void MyCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
    if (e.NewItems != null)
    {
        foreach (object item in e.NewItems)
        {
            if (item is MyItem)
                ((MyItem)item).PropertyChanged += MyItem_PropertyChanged;
        }
    }

    if (e.OldItems != null)
    {
        foreach (object item in e.OldItems)
        {
            if (item is MyItem)
                ((MyItem)item).PropertyChanged -= MyItem_PropertyChanged;
        }
    }
}

...

void MyItem_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
    OnPropertyChanged("MyCollection");
}