misc: extract VMs.

demo/Semi.Avalonia.Demo/ViewModels/RefreshContainerDemoViewModel.cs

@@ -0,0 +1,22 @@
+using System.Collections.ObjectModel;
+using System.Linq;
+using System.Threading.Tasks;
+using CommunityToolkit.Mvvm.ComponentModel;
+
+namespace Semi.Avalonia.Demo.ViewModels;
+
+public class RefreshContainerDemoViewModel : ObservableObject
+{
+    public ObservableCollection<string> Items { get; }
+
+    public RefreshContainerDemoViewModel()
+    {
+        Items = new ObservableCollection<string>(Enumerable.Range(1, 200).Select(i => $"Item {i}"));
+    }
+
+    public async Task AddToTop()
+    {
+        await Task.Delay(1000);
+        Items.Insert(0, $"Item {200 - Items.Count}");
+    }
+}