New WinoListView implementation with multiple selections.

Wino.Mail.WinUI/Controls/ListView/WinoMailItemTemplateSelector.cs

@@ -0,0 +1,22 @@
+using System;
+using Microsoft.UI.Xaml;
+using Microsoft.UI.Xaml.Controls;
+using Wino.Mail.ViewModels.Data;
+
+namespace Wino.Mail.WinUI.Controls.ListView;
+
+public partial class WinoMailItemTemplateSelector : DataTemplateSelector
+{
+    public DataTemplate? SingleMailItemTemplate { get; set; }
+    public DataTemplate? ThreadMailItemTemplate { get; set; }
+
+    protected override DataTemplate SelectTemplateCore(object item, DependencyObject container)
+    {
+        if (item is MailItemViewModel)
+            return SingleMailItemTemplate ?? throw new Exception($"Missing template for single mail items.");
+        else if (item is ThreadMailItemViewModel)
+            return ThreadMailItemTemplate ?? throw new Exception($"Missing template for thread mail items.");
+
+        return base.SelectTemplateCore(item, container);
+    }
+}