Began porting my MultiPageViewModel from the Windows Forms library to the Avalonia library; updated copyright statement for the year 2026

Source/ViewModels/IMultiPageViewModel.cs

@@ -0,0 +1,41 @@
+#region Apache License 2.0
+/*
+Nuclex Foundation libraries for .NET
+Copyright (C) 2002-2026 Markus Ewald / Nuclex Development Labs
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+#endregion // Apache License 2.0
+
+using System;
+
+using Nuclex.Avalonia.Commands;
+
+namespace Nuclex.Avalonia.ViewModels {
+
+  /// <summary>Interface for view models that can switch between different pages</summary>
+  /// <typeparam name="TPageEnumeration">Enum type by which pages can be indicated</typeparam>
+  public interface IMultiPageViewModel<TPageEnumeration> {
+
+    /// <summary>Command to switch the active tool page</summary>
+    IAsyncCommand<TPageEnumeration> SwitchPageCommand { get; }
+
+    /// <summary>The currently displayed page</summary>
+    TPageEnumeration? ActivePage { get; }
+
+    /// <summary>View model for the page that is currently being shown</summary>
+    object? ActivePageViewModel { get; }
+
+  }
+
+} // namespace Nuclex.Avalonia.ViewModels