UI

Toolkit.Foundation/IProvider.cs

@@ -8,4 +8,9 @@ public interface IProvider<TParameter, TService>
 public interface IProvider<TService>
 {
     TService? Get();
+}
+
+public interface ISelectable
+{
+    bool Selected { get; set; }
 }

Toolkit.Foundation/ObservableCollectionViewModel.cs

@@ -97,7 +97,7 @@ public partial class ObservableCollectionViewModel<TViewModel> :
 
     public TViewModel this[int index]
     {
-        get => collection[index];
+        get => Count > 0 ? collection[index] : default;
         set => SetItem(index, value);
     }