Fix #1815: make all documents closeable as long as there is at least one.

ILSpy/Docking/DockWorkspace.cs

@@ -43,6 +43,16 @@ namespace ICSharpCode.ILSpy.Docking
 
 		private DockWorkspace()
 		{
+			this.Documents.CollectionChanged += Documents_CollectionChanged;
+		}
+
+		private void Documents_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
+		{
+			var collection = (PaneCollection<DocumentModel>)sender;
+			bool canClose = collection.Count > 1;
+			foreach (var item in collection) {
+				item.IsCloseable = canClose;
+			}
 		}
 
 		public PaneCollection<DocumentModel> Documents { get; } = new PaneCollection<DocumentModel>();

ILSpy/Docking/PaneCollection.cs

@@ -49,7 +49,7 @@ namespace ICSharpCode.ILSpy.Docking
 			item.IsActive = true;
 		}
 
-		public int Count => observableCollection.Count();
+		public int Count => observableCollection.Count;
 		public bool IsReadOnly => false;
 		public void Clear() => observableCollection.Clear();
 		public bool Contains(T item) => observableCollection.Contains(item);

ILSpy/MainWindow.xaml

@@ -211,7 +211,7 @@
 							<Setter Property="IsSelected" Value="{Binding Model.IsSelected, Mode=TwoWay}"/>
 							<Setter Property="IsActive" Value="{Binding Model.IsActive, Mode=TwoWay}"/>
 							<Setter Property="CloseCommand" Value="{Binding Model.CloseCommand}" />
-							<Setter Property="CanClose" Value="{Binding Model.IsCloseable}" />
+							<Setter Property="CanClose" Value="{Binding Model.IsCloseable, Mode=TwoWay}" />
 						</Style>
 					</docking:PaneStyleSelector.DocumentStyle>
 				</docking:PaneStyleSelector>

ILSpy/MainWindow.xaml.cs

@@ -457,7 +457,6 @@ namespace ICSharpCode.ILSpy
 		void MainWindow_Loaded(object sender, RoutedEventArgs e)
 		{
 			DockWorkspace.Instance.Documents.Add(new DecompiledDocumentModel() {
-				IsCloseable = false,
 				Language = CurrentLanguage,
 				LanguageVersion = CurrentLanguageVersion
 			});

ILSpy/ViewModels/PaneModel.cs

@@ -31,6 +31,14 @@ namespace ICSharpCode.ILSpy.ViewModels
 			public CloseCommandImpl(PaneModel model)
 			{
 				this.model = model;
+				this.model.PropertyChanged += Model_PropertyChanged;
+			}
+
+			private void Model_PropertyChanged(object sender, PropertyChangedEventArgs e)
+			{
+				if (e.PropertyName == nameof(model.IsCloseable)) {
+					CanExecuteChanged?.Invoke(this, EventArgs.Empty);
+				}
 			}
 
 			public event EventHandler CanExecuteChanged;