Try to fix #796: release resources on ALT-F4

QuickLook/ViewWindowManager.cs

@@ -34,7 +34,7 @@ namespace QuickLook
 
         internal ViewWindowManager()
         {
-            _viewerWindow = new ViewerWindow();
+            InitNewViewerWindow();
         }
 
         public void Dispose()
@@ -100,9 +100,7 @@ namespace QuickLook
 
             _viewerWindow.Pinned = true;
 
-            var newWindow = new ViewerWindow();
-
-            _viewerWindow = newWindow;
+            InitNewViewerWindow();
         }
 
         public void SwitchPreview(string path = null)
@@ -168,6 +166,18 @@ namespace QuickLook
                 e.Throw();
         }
 
+        private void InitNewViewerWindow()
+        {
+            _viewerWindow = new ViewerWindow();
+            _viewerWindow.Closed += (sender, e) =>
+            {
+                if (!(sender is ViewerWindow w) || w.Pinned)
+                    return; // Pinned window has already been forgotten
+                StopFocusMonitor();
+                InitNewViewerWindow();
+            };
+        }
+
         internal static ViewWindowManager GetInstance()
         {
             return _instance ?? (_instance = new ViewWindowManager());

QuickLook/ViewerWindow.Actions.cs

@@ -16,6 +16,7 @@
 // along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 using System;
+using System.ComponentModel;
 using System.Diagnostics;
 using System.IO;
 using System.Runtime.ExceptionServices;
@@ -57,7 +58,7 @@ namespace QuickLook
         internal void RunAndClose()
         {
             Run();
-            BeginClose();
+            Close();
         }
 
         private void PositionWindow(Size size)
@@ -276,17 +277,17 @@ namespace QuickLook
             //Dispatcher.BeginInvoke(new Action(Hide), DispatcherPriority.ApplicationIdle);
 
             ViewWindowManager.GetInstance().ForgetCurrentWindow();
-            BeginClose();
+            Close();
 
             ProcessHelper.PerformAggressiveGC();
         }
 
-        internal void BeginClose()
+        protected override void OnClosing(CancelEventArgs e)
         {
             UnloadPlugin();
             busyDecorator.Dispose();
 
-            Close();
+            base.OnClosing(e);
 
             ProcessHelper.PerformAggressiveGC();
         }

QuickLook/ViewerWindow.xaml.cs

@@ -78,7 +78,7 @@ namespace QuickLook
             buttonCloseWindow.Click += (sender, e) =>
             {
                 if (Pinned)
-                    BeginClose();
+                    Close();
                 else
                     ViewWindowManager.GetInstance().ClosePreview();
             };