WPF: binding viewmodel property of type DateTime to Calendar inside ItemsControl

Question

i have a problem with WPF Binding. I want to bind a list of Months to a ItemsControl that shows a Calendar Control for each month. But each rendered Calendar shows DateTime.Now,not the bound DateTimes. Does anyone know why this is happening?

This is what i have so far:

The MainWindow.xaml

<Window x:Class="CalendarListTest.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525">
<Grid>
    <ItemsControl x:Name="calendarList">
        <ItemsControl.ItemTemplate>
            <DataTemplate>
                <Calendar DisplayDate="{Binding CurrentDate}" />
            </DataTemplate>
        </ItemsControl.ItemTemplate>
    </ItemsControl>
</Grid>

** The place where the collection is assigned to the ItemsSource**

        private void Window_Loaded( object sender, RoutedEventArgs e )
    {
        CalendarList list = new CalendarList( );
        list.Add( new CalendarMonth( ) { CurrentDate = DateTime.Parse( "1.1.1979" ) } );
        list.Add( new CalendarMonth( ) { CurrentDate = DateTime.Parse( "1.2.1979" ) } );
        list.Add( new CalendarMonth( ) { CurrentDate = DateTime.Parse( "1.3.1979" ) } );

        calendarList.ItemsSource = list;
    }

The CalendarMonth ViewModel:

public class CalendarMonth
{
    private DateTime _currentDate;

    public DateTime CurrentDate
    {
        get { return _currentDate; }
        set { _currentDate = value; }
    }

}

And the Collection to bind to the ItemsControl:

public class CalendarList : ObservableCollection<CalendarMonth>
{
}

Now, the result:

Why is this happening?

edit: When providing <Calendar DisplayDate="{Binding CurrentDate, Mode=OneWay}" /> the binding works.

Answer 1

The issue appears to be with how the Calendar initializes the DisplayDate property. It currently does it like this:

public Calendar() {
    // ...
    base.SetCurrentValueInternal(DisplayDateProperty, DateTime.Today);
}

It appears that even though the DisplayDate is being initialized before the binding is established, it will still be pushed back to the binding source as if it were set after. This is most likely a bug.

You can work around it using something like:

public class MyCalendar : Calendar {
    public MyCalendar() {
        this.ClearValue(DisplayDateProperty);
    }
}

Or you could establish the binding at a later time (i.e. when the Calendar is loaded) using an event handler or attached behavior.

Answer 2

Does this fit your needs?

<Calendar SelectedDate="{Binding Path=CurrentDate}"
          DisplayDate="{Binding Path=SelectedDate,
                                RelativeSource={RelativeSource Self}, 
                                Mode=OneWay}" />