feat: WIP.

demo/Ursa.Demo/Pages/DatePickerDemo.axaml

@@ -8,6 +8,6 @@
     <StackPanel Margin="20" HorizontalAlignment="Left">
         <u:CalendarMonthView />
         <u:CalendarYearView />
-        <u:Calendar/>
+        <u:CalendarDisplayControl/>
     </StackPanel>
 </UserControl>

src/Ursa.Themes.Semi/Controls/Calendar.axaml

@@ -5,7 +5,7 @@
     <Design.PreviewWith>
         <StackPanel Margin="20" Spacing="5">
             <u:CalendarMonthView />
-            <u:Calendar />
+            <u:CalendarDisplayControl />
         </StackPanel>
     </Design.PreviewWith>
     <!--  Add Resources Here  -->
@@ -120,15 +120,15 @@
         </Style>
     </ControlTheme>
 
-    <ControlTheme x:Key="{x:Type u:Calendar}" TargetType="u:Calendar">
+    <ControlTheme x:Key="{x:Type u:CalendarDisplayControl}" TargetType="u:CalendarDisplayControl">
         <Setter Property="MinHeight" Value="300" />
         <Setter Property="Template">
-            <ControlTemplate TargetType="u:Calendar">
+            <ControlTemplate TargetType="u:CalendarDisplayControl">
                 <Panel>
                     <Grid RowDefinitions="Auto, *">
                         <Grid Grid.Row="0" ColumnDefinitions="Auto, Auto,*, Auto, Auto">
                             <Button
-                                Name="{x:Static u:Calendar.PART_PreviousYearButton}"
+                                Name="{x:Static u:CalendarDisplayControl.PART_PreviousYearButton}"
                                 Grid.Column="0"
                                 HorizontalContentAlignment="Left"
                                 Foreground="{TemplateBinding Foreground}"
@@ -141,7 +141,7 @@
                             </Button>
 
                             <Button
-                                Name="{x:Static u:Calendar.PART_PreviousButton}"
+                                Name="{x:Static u:CalendarDisplayControl.PART_PreviousButton}"
                                 Grid.Column="1"
                                 HorizontalContentAlignment="Left"
                                 Foreground="{TemplateBinding Foreground}"
@@ -155,7 +155,7 @@
 
                             <Grid Grid.Column="2" ColumnDefinitions="*, *">
                                 <Button
-                                    Name="{x:Static u:Calendar.PART_YearButton}"
+                                    Name="{x:Static u:CalendarDisplayControl.PART_YearButton}"
                                     Grid.Column="0"
                                     HorizontalContentAlignment="Center"
                                     Content="2024"
@@ -163,7 +163,7 @@
                                     IsVisible="{TemplateBinding IsMonthMode}"
                                     Theme="{DynamicResource BorderlessButton}" />
                                 <Button
-                                    Name="{x:Static u:Calendar.PART_MonthButton}"
+                                    Name="{x:Static u:CalendarDisplayControl.PART_MonthButton}"
                                     Grid.Column="1"
                                     HorizontalContentAlignment="Center"
                                     Content="Apr"
@@ -171,7 +171,7 @@
                                     IsVisible="{TemplateBinding IsMonthMode}"
                                     Theme="{DynamicResource BorderlessButton}" />
                                 <Button
-                                    Name="{x:Static u:Calendar.PART_HeaderButton}"
+                                    Name="{x:Static u:CalendarDisplayControl.PART_HeaderButton}"
                                     Grid.Column="0"
                                     Grid.ColumnSpan="2"
                                     IsVisible="{TemplateBinding IsMonthMode, Converter={x:Static BoolConverters.Not}}"
@@ -181,7 +181,7 @@
                             </Grid>
 
                             <Button
-                                Name="{x:Static u:Calendar.PART_NextButton}"
+                                Name="{x:Static u:CalendarDisplayControl.PART_NextButton}"
                                 Grid.Column="3"
                                 HorizontalContentAlignment="Left"
                                 Foreground="{TemplateBinding Foreground}"
@@ -193,7 +193,7 @@
                                     Foreground="{DynamicResource CalendarItemIconForeground}" />
                             </Button>
                             <Button
-                                Name="{x:Static u:Calendar.PART_NextYearButton}"
+                                Name="{x:Static u:CalendarDisplayControl.PART_NextYearButton}"
                                 Grid.Column="4"
                                 HorizontalContentAlignment="Left"
                                 Foreground="{TemplateBinding Foreground}"
@@ -206,12 +206,12 @@
                             </Button>
                         </Grid>
                         <u:CalendarMonthView
-                            Name="{x:Static u:Calendar.PART_MonthView}"
+                            Name="{x:Static u:CalendarDisplayControl.PART_MonthView}"
                             Grid.Row="1"
                             VerticalAlignment="Top"
                             IsVisible="{TemplateBinding IsMonthMode}" />
                         <u:CalendarYearView
-                            Name="{x:Static u:Calendar.PART_YearView}"
+                            Name="{x:Static u:CalendarDisplayControl.PART_YearView}"
                             Grid.Row="1"
                             Width="{Binding #PART_MonthView.Bounds.Width}"
                             Height="{Binding #PART_MonthView.Bounds.Height}"

src/Ursa/Controls/DateTimePicker/CalendarDayButton.cs

@@ -1,19 +1,17 @@
-using Avalonia;
+using Avalonia.Controls;
-using Avalonia.Controls;
 using Avalonia.Controls.Metadata;
 using Avalonia.Controls.Mixins;
 using Avalonia.Controls.Primitives;
 using Avalonia.Input;
 using Avalonia.Interactivity;
 using Irihi.Avalonia.Shared.Common;
-using Irihi.Avalonia.Shared.Helpers;
-using Ursa.EventArgs;
 
 namespace Ursa.Controls;
 
-[PseudoClasses(PseudoClassName.PC_Pressed, PseudoClassName.PC_Selected, 
+[PseudoClasses(PseudoClassName.PC_Pressed, PseudoClassName.PC_Selected,
-    PC_StartDate, PC_EndDate, PC_PreviewStartDate, PC_PreviewEndDate, PC_InRange, PC_Today, PC_Blackout, PC_NotCurrentMonth)]
+    PC_StartDate, PC_EndDate, PC_PreviewStartDate, PC_PreviewEndDate, PC_InRange, PC_Today, PC_Blackout,
-public class CalendarDayButton: ContentControl
+    PC_NotCurrentMonth)]
+public class CalendarDayButton : ContentControl
 {
     public const string PC_StartDate = ":start-date";
     public const string PC_EndDate = ":end-date";
@@ -23,10 +21,46 @@ public class CalendarDayButton: ContentControl
     public const string PC_Today = ":today";
     public const string PC_NotCurrentMonth = ":not-current-month";
     public const string PC_Blackout = ":blackout";
-    
+
-    internal Calendar? Owner { get; set; }
+    private static HashSet<string> _pseudoClasses =
+    [
+        PseudoClassName.PC_Selected, PC_EndDate, PC_PreviewStartDate, 
+        PC_PreviewEndDate, PseudoClassName.PC_Selected, PC_InRange
+    ];
+
+    public static readonly RoutedEvent<CalendarDayButtonEventArgs> DateSelectedEvent =
+        RoutedEvent.Register<CalendarDayButton, CalendarDayButtonEventArgs>(
+            nameof(DateSelected), RoutingStrategies.Bubble);
+
+    public static readonly RoutedEvent<CalendarDayButtonEventArgs> DatePreviewedEvent =
+        RoutedEvent.Register<CalendarDayButton, CalendarDayButtonEventArgs>(
+            nameof(DatePreviewed), RoutingStrategies.Bubble);
+
+    private bool _isBlackout;
+
+    private bool _isEndDate;
+
+    private bool _isInRange;
+
+    private bool _isNotCurrentMonth;
+
+    private bool _isPreviewEndDate;
+
+    private bool _isPreviewStartDate;
+
+    private bool _isSelected;
+
+    private bool _isStartDate;
 
     private bool _isToday;
+
+    static CalendarDayButton()
+    {
+        PressedMixin.Attach<CalendarDayButton>();
+    }
+
+    // internal CalendarDisplayControl? Owner { get; set; }
+
     public bool IsToday
     {
         get => _isToday;
@@ -36,30 +70,27 @@ public class CalendarDayButton: ContentControl
             PseudoClasses.Set(PC_Today, value);
         }
     }
-    
+
-    private bool _isStartDate;
     public bool IsStartDate
     {
         get => _isStartDate;
         set
         {
             _isStartDate = value;
-            PseudoClasses.Set(PC_StartDate, value);
+            SetPseudoClass(PC_StartDate);
         }
     }
-    
+
-    private bool _isEndDate;
     public bool IsEndDate
     {
         get => _isEndDate;
         set
         {
             _isEndDate = value;
-            PseudoClasses.Set(PC_EndDate, value);
+            SetPseudoClass(PC_EndDate);
         }
     }
-    
+
-    private bool _isPreviewStartDate;
     public bool IsPreviewStartDate
     {
         get => _isPreviewStartDate;
@@ -69,8 +100,7 @@ public class CalendarDayButton: ContentControl
             PseudoClasses.Set(PC_PreviewStartDate, value);
         }
     }
-    
+
-    private bool _isPreviewEndDate;
     public bool IsPreviewEndDate
     {
         get => _isPreviewEndDate;
@@ -80,8 +110,7 @@ public class CalendarDayButton: ContentControl
             PseudoClasses.Set(PC_PreviewEndDate, value);
         }
     }
-    
+
-    private bool _isInRange;
     public bool IsInRange
     {
         get => _isInRange;
@@ -92,7 +121,6 @@ public class CalendarDayButton: ContentControl
         }
     }
 
-    private bool _isSelected;
     public bool IsSelected
     {
         get => _isSelected;
@@ -102,10 +130,9 @@ public class CalendarDayButton: ContentControl
             PseudoClasses.Set(PseudoClassName.PC_Selected, value);
         }
     }
-    
+
-    private bool _isBlackout;
     /// <summary>
-    /// Notice: IsBlackout is not equivalent to not IsEnabled. Blackout dates still react to pointerover actions. 
+    ///     Notice: IsBlackout is not equivalent to not IsEnabled. Blackout dates still react to pointerover actions.
     /// </summary>
     public bool IsBlackout
     {
@@ -116,10 +143,10 @@ public class CalendarDayButton: ContentControl
             PseudoClasses.Set(PC_Blackout, value);
         }
     }
-    
+
-    private bool _isNotCurrentMonth;
     /// <summary>
-    /// Notice: IsNotCurrentMonth is not equivalent to not IsEnabled. Not current month dates still react to pointerover and press action. 
+    ///     Notice: IsNotCurrentMonth is not equivalent to not IsEnabled. Not current month dates still react to pointerover
+    ///     and press action.
     /// </summary>
     public bool IsNotCurrentMonth
     {
@@ -130,33 +157,23 @@ public class CalendarDayButton: ContentControl
             PseudoClasses.Set(PC_NotCurrentMonth, value);
         }
     }
-    
+
-    public static readonly RoutedEvent<CalendarDayButtonEventArgs> DateSelectedEvent = RoutedEvent.Register<CalendarDayButton, CalendarDayButtonEventArgs>(
-        nameof(DateSelected), RoutingStrategies.Bubble);
-    
     public event EventHandler<CalendarDayButtonEventArgs> DateSelected
     {
         add => AddHandler(DateSelectedEvent, value);
         remove => RemoveHandler(DateSelectedEvent, value);
     }
-    
+
-    public static readonly RoutedEvent<CalendarDayButtonEventArgs> DatePreviewedEvent = RoutedEvent.Register<CalendarDayButton, CalendarDayButtonEventArgs>(
-        nameof(DatePreviewed), RoutingStrategies.Bubble);
-    
     public event EventHandler<CalendarDayButtonEventArgs> DatePreviewed
     {
         add => AddHandler(DateSelectedEvent, value);
-        remove => RemoveHandler(DateSelectedEvent, value); 
+        remove => RemoveHandler(DateSelectedEvent, value);
-    }
-
-    static CalendarDayButton()
-    {
-        PressedMixin.Attach<CalendarDayButton>();
     }
 
     protected override void OnApplyTemplate(TemplateAppliedEventArgs e)
     {
         base.OnApplyTemplate(e);
+        /*
         PseudoClasses.Set(PC_Today, IsToday);
         PseudoClasses.Set(PC_StartDate, IsStartDate);
         PseudoClasses.Set(PC_EndDate, IsEndDate);
@@ -164,23 +181,40 @@ public class CalendarDayButton: ContentControl
         PseudoClasses.Set(PC_PreviewEndDate, IsPreviewEndDate);
         PseudoClasses.Set(PC_InRange, IsInRange);
         PseudoClasses.Set(PseudoClassName.PC_Selected, IsSelected);
+        */
     }
-    
+
     protected override void OnPointerPressed(PointerPressedEventArgs e)
     {
         base.OnPointerPressed(e);
-        if (this.DataContext is DateTime d)
+        if (DataContext is DateTime d)
-        {
             RaiseEvent(new CalendarDayButtonEventArgs(d) { RoutedEvent = DateSelectedEvent, Source = this });
-        }
     }
 
     protected override void OnPointerEntered(PointerEventArgs e)
     {
         base.OnPointerEntered(e);
-        if (this.DataContext is DateTime d)
+        if (DataContext is DateTime d)
-        {
             RaiseEvent(new CalendarDayButtonEventArgs(d) { RoutedEvent = DateSelectedEvent, Source = this });
+    }
+
+    internal void ResetSelection()
+    {
+        foreach (var pc in _pseudoClasses)
+        {
+            PseudoClasses.Set(pc, false);
         }
     }
+
+    private void SetPseudoClass(string s)
+    {
+        if (_pseudoClasses.Contains(s))
+        {
+            foreach (var pc in _pseudoClasses)
+            {
+                PseudoClasses.Set(pc, false);
+            }
+        }
+        PseudoClasses.Set(s, true);
+    }
 }

src/Ursa/Controls/DateTimePicker/CalendarDisplayControl.cs

@@ -17,7 +17,7 @@ namespace Ursa.Controls;
 [TemplatePart(PART_HeaderButton, typeof(Button))]
 [TemplatePart(PART_MonthView, typeof(CalendarMonthView))]
 [TemplatePart(PART_YearView, typeof(CalendarYearView))]
-public class Calendar: TemplatedControl
+public class CalendarDisplayControl: TemplatedControl
 {
     public const string PART_NextYearButton = "PART_NextYearButton";
     public const string PART_PreviousYearButton = "PART_PreviousYearButton";
@@ -37,7 +37,7 @@ public class Calendar: TemplatedControl
     private Button? _headerButton;
     
     
-    public static readonly StyledProperty<DateTime> SelectedDateProperty = AvaloniaProperty.Register<Calendar, DateTime>(nameof(SelectedDate), DateTime.Now);
+    public static readonly StyledProperty<DateTime> SelectedDateProperty = AvaloniaProperty.Register<CalendarDisplayControl, DateTime>(nameof(SelectedDate), DateTime.Now);
     public DateTime SelectedDate
     {
         get => GetValue(SelectedDateProperty);
@@ -45,7 +45,7 @@ public class Calendar: TemplatedControl
     }
 
     public static readonly StyledProperty<DayOfWeek> FirstDayOfWeekProperty =
-        AvaloniaProperty.Register<Calendar, DayOfWeek>(nameof(FirstDayOfWeek),
+        AvaloniaProperty.Register<CalendarDisplayControl, DayOfWeek>(nameof(FirstDayOfWeek),
             defaultValue: DateTimeHelper.GetCurrentDateTimeFormatInfo().FirstDayOfWeek);
     public DayOfWeek FirstDayOfWeek
     {
@@ -53,7 +53,7 @@ public class Calendar: TemplatedControl
         set => SetValue(FirstDayOfWeekProperty, value);
     }
 
-    public static readonly StyledProperty<bool> IsTodayHighlightedProperty = AvaloniaProperty.Register<Calendar, bool>(nameof(IsTodayHighlighted), true);
+    public static readonly StyledProperty<bool> IsTodayHighlightedProperty = AvaloniaProperty.Register<CalendarDisplayControl, bool>(nameof(IsTodayHighlighted), true);
     public bool IsTodayHighlighted
     {
         get => GetValue(IsTodayHighlightedProperty);
@@ -61,7 +61,7 @@ public class Calendar: TemplatedControl
     }
 
     public static readonly StyledProperty<AvaloniaList<DateRange>?> BlackoutDatesProperty =
-        AvaloniaProperty.Register<Calendar, AvaloniaList<DateRange>?>(
+        AvaloniaProperty.Register<CalendarDisplayControl, AvaloniaList<DateRange>?>(
             nameof(BlackoutDates));
 
     public AvaloniaList<DateRange>? BlackoutDates
@@ -70,7 +70,7 @@ public class Calendar: TemplatedControl
         set => SetValue(BlackoutDatesProperty, value);
     }
 
-    public static readonly StyledProperty<IDateSelector?> BlackoutDateRuleProperty = AvaloniaProperty.Register<Calendar, IDateSelector?>(
+    public static readonly StyledProperty<IDateSelector?> BlackoutDateRuleProperty = AvaloniaProperty.Register<CalendarDisplayControl, IDateSelector?>(
         nameof(BlackoutDateRule));
 
     public IDateSelector? BlackoutDateRule
@@ -81,7 +81,7 @@ public class Calendar: TemplatedControl
 
     private bool _isMonthMode = true;
 
-    public static readonly DirectProperty<Calendar, bool> IsMonthModeProperty = AvaloniaProperty.RegisterDirect<Calendar, bool>(
+    public static readonly DirectProperty<CalendarDisplayControl, bool> IsMonthModeProperty = AvaloniaProperty.RegisterDirect<CalendarDisplayControl, bool>(
         nameof(IsMonthMode), o => o.IsMonthMode, (o, v) => o.IsMonthMode = v);
 
     public bool IsMonthMode
@@ -153,14 +153,14 @@ public class Calendar: TemplatedControl
     {
         SetCurrentValue(IsMonthModeProperty, false);
         if (_yearView is null) return;
-        _headerButton?.SetValue(Button.ContentProperty, _yearView.ContextDate.Year);
+        _headerButton?.SetValue(ContentControl.ContentProperty, _yearView.ContextDate.Year);
         _yearView?.UpdateMode(CalendarYearViewMode.Month);
     }
 
     private void OnYearButtonClick(object sender, RoutedEventArgs e)
     {
         if (_yearView is null) return;
-        _headerButton?.SetValue(Button.ContentProperty,
+        _headerButton?.SetValue(ContentControl.ContentProperty,
             _yearView?.ContextDate.Year + "-" + (_yearView?.ContextDate.Year + 10));
         _yearView?.UpdateMode(CalendarYearViewMode.Year);
         SetCurrentValue(IsMonthModeProperty, false);

src/Ursa/Controls/DateTimePicker/CalendarMonthView.cs

@@ -9,7 +9,8 @@ using Avalonia.Layout;
 namespace Ursa.Controls;
 
 /// <summary>
-///     Show days in a month.
+/// Show days in a month. CalendarMonthView itself doesn't handle any date range selection logic.
+/// it provides a method to mark preview range and selection range. The range limit may out of current displayed month. 
 /// </summary>
 [TemplatePart(PART_Grid, typeof(Grid))]
 public class CalendarMonthView : TemplatedControl
@@ -32,7 +33,7 @@ public class CalendarMonthView : TemplatedControl
             view.OnDayOfWeekChanged(args));
     }
 
-    internal Calendar? Owner { get; set; }
+    internal CalendarDisplayControl? Owner { get; set; }
 
     /// <summary>
     ///     The DateTime used to generate the month view. This date will be within the month.
@@ -156,6 +157,30 @@ public class CalendarMonthView : TemplatedControl
     public event EventHandler<CalendarDayButtonEventArgs>? OnDateSelected;
     public event EventHandler<CalendarDayButtonEventArgs>? OnDatePreviewed;
 
+    public void MarkDates(DateTime? startDate = null, DateTime? endDate = null, DateTime? previewStartDate = null, DateTime? previewEndDate = null)
+    {
+        if (_grid?.Children is null) return;
+        DateTime start = startDate ?? DateTime.MaxValue;
+        DateTime end = endDate ?? DateTime.MinValue;
+        DateTime previewStart = previewStartDate ?? DateTime.MaxValue;
+        DateTime previewEnd = previewEndDate ?? DateTime.MinValue;
+        DateTime rangeStart = DateTimeHelper.Min(start, previewStart);
+        DateTime rangeEnd = DateTimeHelper.Max(end, previewEnd);
+        foreach (var child in _grid.Children)
+        {
+            if (child is not CalendarDayButton { DataContext: DateTime d } button) continue;
+            if(d.Month != _contextDate.Month) continue;
+            button.ResetSelection();
+            if (d < rangeEnd && d > rangeStart) button.IsInRange = true;
+            if (d == previewStart) button.IsPreviewStartDate = true;
+            if (d == previewEnd) button.IsPreviewEndDate = true;
+            if (d == startDate) button.IsStartDate = true;
+            if (d == endDate) button.IsEndDate = true;
+            if (d == startDate && d == endDate) button.IsSelected = true;
+        }
+    }
+    
+    [Obsolete]
     public void MarkSelection(DateTime? start, DateTime? end)
     {
         if (_grid?.Children is null) return;

src/Ursa/Controls/DateTimePicker/CalendarYearButton.cs

@@ -12,39 +12,43 @@ internal enum CalendarYearViewMode
 {
     Month,
     Year,
+
     // The button represents 10 years. 
-    YearRange,
+    YearRange
-} 
+}
 
 [PseudoClasses(PC_Range, PseudoClassName.PC_Selected)]
-public class CalendarYearButton: ContentControl
+public class CalendarYearButton : ContentControl
 {
     public const string PC_Range = ":range";
+
+    public static readonly RoutedEvent<CalendarYearButtonEventArgs> ItemSelectedEvent =
+        RoutedEvent.Register<CalendarYearButton, CalendarYearButtonEventArgs>(
+            nameof(ItemSelected), RoutingStrategies.Bubble);
+
     static CalendarYearButton()
     {
         PressedMixin.Attach<CalendarYearButton>();
     }
-    
+
     internal int Year { get; private set; }
-    
+
     internal int Month { get; private set; }
-    
+
     internal int StartYear { get; private set; }
-    
+
     internal int EndYear { get; private set; }
-    
+
     internal CalendarYearViewMode Mode { get; private set; }
-    
+
-    public static readonly RoutedEvent<CalendarYearButtonEventArgs> ItemSelectedEvent = RoutedEvent.Register<CalendarYearButton, CalendarYearButtonEventArgs>(
-        nameof(ItemSelected), RoutingStrategies.Bubble);
-    
     public event EventHandler<CalendarDayButtonEventArgs> ItemSelected
     {
         add => AddHandler(ItemSelectedEvent, value);
         remove => RemoveHandler(ItemSelectedEvent, value);
     }
 
-    internal void SetValues(CalendarYearViewMode mode, DateTime contextDate, int? month = null, int? year = null, int? startYear = null, int? endYear = null)
+    internal void SetValues(CalendarYearViewMode mode, DateTime contextDate, int? month = null, int? year = null,
+        int? startYear = null, int? endYear = null)
     {
         Debug.Assert(!(month is null && year is null && startYear is null && endYear is null));
         Mode = mode;
@@ -66,6 +70,5 @@ public class CalendarYearButton: ContentControl
         base.OnPointerPressed(e);
         RaiseEvent(new CalendarYearButtonEventArgs(Mode, Year, Month, StartYear, EndYear)
             { RoutedEvent = ItemSelectedEvent, Source = this });
-
     }
 }

src/Ursa/Controls/DateTimePicker/CalendarYearButtonEventArgs.cs

@@ -4,12 +4,14 @@ namespace Ursa.Controls;
 
 public class CalendarYearButtonEventArgs: RoutedEventArgs
 {
-    internal int? Year { get; }
+    public int? Year { get; }
-    internal int? Month { get; }
+    public int? Month { get; }
-    internal int? StartYear { get; }
+    public int? StartYear { get; }
-    internal int? EndYear { get; }
+    public int? EndYear { get; }
     internal CalendarYearViewMode Mode { get; }
-    internal CalendarYearButtonEventArgs( CalendarYearViewMode mode, int? year, int? month, int? startYear, int? endYear )
+
+    /// <inheritdoc />
+    internal CalendarYearButtonEventArgs(CalendarYearViewMode mode, int? year, int? month, int? startYear, int? endYear )
     {
         Year = year;
         Month = month;

src/Ursa/Controls/DateTimePicker/DateTimeHelper.cs

@@ -32,5 +32,14 @@ internal static class DateTimeHelper
     {
         return (dt1.Year - dt2.Year) * 12 + dt1.Month - dt2.Month;
     }
-    
+
+    public static DateTime Min(DateTime d1, DateTime d2)
+    {
+        return d1.Ticks > d2.Ticks ? d2 : d1;
+    }
+
+    public static DateTime Max(DateTime d1, DateTime d2)
+    {
+        return d1.Ticks < d2.Ticks ? d2 : d1;
+    }
 }