Extending WPF Calendar to support selecting many dates at once - wpf

Question

I want to add a method to the WPF Calendar control to enable it to select many dates at once, and raise the SelectedDatesChangedEvent only once at the end.
The WPF Calendar control allows you to add only one date at a time (ranges are not useful to me). However I might need to add some 1000 dates and I don't want the SelectedDatesChangedEvent handler called 1000 times because in my case it's an expensive operation.
The WPF DataGrid has a very nice feature that allows for this to be done:
public class MyDataGrid : DataGrid
{
public void ClearAndSelectMany(IEnumerable<DateTime> datesToBeSelected)
{
this.BeginUpdateSelectedItems();
...
foreach (DateTime date in datesToBeSelected)
this.SelectedDates.Add(date);
...
this.EndUpdateSelectedItems();
}
}
However the Calendar doesn't have anything like DataGrid's BeginUpdateSelectedItems(), so I'm trying to create a workaround by preventing base.OnSelectedDatesChanged() being called until it's all done:
public class MyCalendar : Calendar
{
protected override void OnSelectedDatesChanged(SelectionChangedEventArgs e)
{
if (false == this.temporaryDontReportSelectionChanged)
base.OnSelectedDatesChanged(e); // this is where I get an exception
}
public void ClearAndSelectMany(IEnumerable<DateTime> datesToBeSelected)
{
this.temporaryDontReportSelectionChanged = true;
...
foreach (DateTime date in datesToBeSelected)
SelectedDates.Add(date);
...
this.temporaryDontReportSelectionChanged = false;
OnSelectedDatesChanged(
new SelectionChangedEventArgs(
MyCalendar.SelectedDatesChangedEvent,
removedDates.ToList(),
addedDates.ToList()));
}
}
Now my problem is that I'm getting an exception when calling base.OnSelectedDatesChanged():
Unable to cast object of type
'System.EventHandler`1[System.Windows.Controls.SelectionChangedEventArgs]'
to type
'System.Windows.Controls.SelectionChangedEventHandler'.
I suppose I didn't properly create the SelectionChangedEventArgs object near the end, but I have no idea how to do it right. Any help will be appreciated.
Update: Motivated by Jamleck's question, I recreated the problem in a new project, and now have a bit more information to provide. Here's the MyCalendar class:
public class MyCalendar : System.Windows.Controls.Calendar
{
private bool temporaryDontReportSelectionChanged;
public MyCalendar()
{
// removing this line below makes my problem go away and it works ok
this.SelectedDatesChanged += MyCalendar_SelectedDatesChanged;
}
void MyCalendar_SelectedDatesChanged(object sender, SelectionChangedEventArgs e)
{
}
protected override void OnSelectedDatesChanged(SelectionChangedEventArgs e)
{
if (!temporaryDontReportSelectionChanged)
base.OnSelectedDatesChanged(e);
}
public void ClearAndSelectMany(IEnumerable<DateTime> datesToBeSelected)
{
this.temporaryDontReportSelectionChanged = true;
...
foreach (DateTime date in datesToBeSelected)
SelectedDates.Add(date);
...
this.temporaryDontReportSelectionChanged = false;
OnSelectedDatesChanged(
new SelectionChangedEventArgs(
MyCalendar.SelectedDatesChangedEvent,
removedDates.ToList(),
addedDates.ToList()));
}
}
So if I don't add an event handler to the SelectedDatesChanged event handler, everything works great, but if I do add it, then I get the InvalidCastException described above.