ObservableCollection + CollectionChanged event + ResourceDictionnary

public ObservableCollection ListeTache
        {
            get { return this._listeTache; }
            set
            {
                _listeTache = value;
                if (PropertyChanged != null)
                {
                    PropertyChanged(this, new PropertyChangedEventArgs("ListeTache"));
                }
            }
        }

        public string Notes
        {
            get { return this._notes; }
            set
            {
                _notes = value;
                if (PropertyChanged != null)
                {
                    PropertyChanged(this, new PropertyChangedEventArgs("Notes"));
                }
            }
        }

public bool Enabled
        {
            get { return _enabled; }
            set
            {
                _enabled = value;
                if (PropertyChanged != null)
                {
                    PropertyChanged(this, new PropertyChangedEventArgs("Enabled"));
                }
            } }

public Day(){
            _listeTache = new ObservableCollection();
            _listeTache.CollectionChanged += ListeTache_Changed;
        }

        private void ListeTache_Changed(object sender, NotifyCollectionChangedEventArgs e)
        {
            MessageBox.Show("ok"); 
}

<TextBox IsEnabled="{Binding IsEnabled}" Text="{Binding Notes, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" AcceptsReturn="True" TextWrapping="Wrap" BorderThickness="0" ScrollViewer.VerticalScrollBarVisibility="Auto" removed="{x:Null}" Foreground="White" />

<ListBox x:Name="ListeTaches" IsEnabled="{Binding IsEnabled}" ItemsSource="{Binding ListeTache}" IsSynchronizedWithCurrentItem="True" FontSize="10" PreviewMouseDown="PreviewMouseDownClick_clear" MouseDoubleClick="doubleClic">
<Style.Triggers>

private void Day_Changed(object sender, PropertyChangedEventArgs e)
        {
            if (DayChanged == null)
            {
                return;
            }

            DayChanged(this, new DayChangedEventArgs(sender as Day));
        }

<Scan:Calendar x:Name="Calendar" DayChanged="Calendar_DayChanged" Margin="0,82,0,0" HorizontalContentAlignment="Center"/>