win2d -> skia, some improvements on rendering.

Wino.Mail.WinUI/Controls/Calendar/CustomCalendarFlipView.cs

@@ -1,5 +1,8 @@
-using Microsoft.UI.Xaml.Automation.Peers;
+using System.Linq;
+using Microsoft.UI.Xaml;
+using Microsoft.UI.Xaml.Automation.Peers;
 using Microsoft.UI.Xaml.Controls;
+using Wino.Mail.WinUI.Controls.CalendarFlipView;
 
 namespace Wino.Calendar.Controls;
 
@@ -11,21 +14,37 @@ public partial class CustomCalendarFlipView : FlipView
     private const string PART_PreviousButton = "PreviousButtonHorizontal";
     private const string PART_NextButton = "NextButtonHorizontal";
 
-    private Button PreviousButton;
-    private Button NextButton;
+    private Button? PreviousButton;
+    private Button? NextButton;
 
     protected override void OnApplyTemplate()
     {
         base.OnApplyTemplate();
 
-        PreviousButton = GetTemplateChild(PART_PreviousButton) as Button;
-        NextButton = GetTemplateChild(PART_NextButton) as Button;
+        PreviousButton = (Button)GetTemplateChild(PART_PreviousButton);
+        NextButton = (Button)GetTemplateChild(PART_NextButton);
 
         // Hide navigation buttons
         PreviousButton.Opacity = NextButton.Opacity = 0;
         PreviousButton.IsHitTestVisible = NextButton.IsHitTestVisible = false;
+
+        this.SelectionChanged += FlipViewSelectionChanged;
     }
 
+    private void FlipViewSelectionChanged(object sender, SelectionChangedEventArgs e) => OnSelectedItemChanged(e.RemovedItems.FirstOrDefault(), e.AddedItems.FirstOrDefault());
+
+    protected virtual void OnSelectedItemChanged(object oldValue, object newValue) { }
+
+    protected override void PrepareContainerForItemOverride(DependencyObject element, object item)
+    {
+        base.PrepareContainerForItemOverride(element, item);
+        OnContainerPrepared(element, item);
+    }
+
+    protected virtual void OnContainerPrepared(DependencyObject element, object item) { }
+
+    protected override DependencyObject GetContainerForItemOverride() => new WinoCalendarFlyoutItem();
+
     public void GoPreviousFlip()
     {
         var backPeer = new ButtonAutomationPeer(PreviousButton);