如何在日历控件中预先选择多个月份- WPF

<Calendar SelectionMode="MultipleRange" SelectionChanged="Calendar_SelectionChanged">
    <Calendar.Template>
        <ControlTemplate TargetType="Calendar">
            <ItemsControl ItemsSource="{Binding SelectedMonths}">
                <ItemsControl.ItemsPanel>
                    <ItemsPanelTemplate>
                        <StackPanel Orientation="Horizontal" />
                    </ItemsPanelTemplate>
                </ItemsControl.ItemsPanel>
                <ItemsControl.ItemTemplate>
                    <DataTemplate>
                        <ToggleButton Content="{Binding}" IsChecked="{Binding IsSelected}" />
                    </DataTemplate>
                </ItemsControl.ItemTemplate>
            </ItemsControl>
        </ControlTemplate>
    </Calendar.Template>
</Calendar>

public class ViewModel : INotifyPropertyChanged
{
    private ObservableCollection<DateTime> selectedMonths;

    public ObservableCollection<DateTime> SelectedMonths
    {
        get { return selectedMonths; }
        set
        {
            selectedMonths = value;
            OnPropertyChanged(nameof(SelectedMonths));
        }
    }

    public ViewModel()
    {
        SelectedMonths = new ObservableCollection<DateTime>();
    }

    private void Calendar_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        foreach (var addedDate in e.AddedItems)
        {
            SelectedMonths.Add((DateTime)addedDate);
        }

        foreach (var removedDate in e.RemovedItems)
        {
            SelectedMonths.Remove((DateTime)removedDate);
        }
    }

    // INotifyPropertyChanged implementation
    // ...
}