move TaskbarList interop into UnmanagedMethods and a wrapper class.

src/Windows/Avalonia.Win32/ITaskBarList2VTable.cs

@@ -1,22 +0,0 @@
-using System;
-using System.Runtime.InteropServices;
-using static Avalonia.Win32.Interop.UnmanagedMethods;
-
-namespace Avalonia.Win32
-{
-    delegate void MarkFullscreenWindow(IntPtr This, IntPtr hwnd, [MarshalAs(UnmanagedType.Bool)] bool fullscreen);
-    delegate HRESULT HrInit(IntPtr This);
-
-    struct ITaskBarList2VTable
-    {
-        public IntPtr IUnknown1;
-        public IntPtr IUnknown2;
-        public IntPtr IUnknown3;
-        public IntPtr HrInit;
-        public IntPtr AddTab;
-        public IntPtr DeleteTab;
-        public IntPtr ActivateTab;
-        public IntPtr SetActiveAlt;
-        public IntPtr MarkFullscreenWindow;
-    }
-}

src/Windows/Avalonia.Win32/Interop/TaskBarList.cs

@@ -0,0 +1,55 @@
+using System;
+using System.Runtime.InteropServices;
+using static Avalonia.Win32.Interop.UnmanagedMethods;
+
+namespace Avalonia.Win32.Interop
+{
+    internal class TaskBarList
+    {
+        private static IntPtr s_taskBarList;
+        private static HrInit s_hrInitDelegate;
+        private static MarkFullscreenWindow s_markFullscreenWindowDelegate;
+
+        /// <summary>
+        /// Ported from https://github.com/chromium/chromium/blob/master/ui/views/win/fullscreen_handler.cc
+        /// </summary>
+        /// <param name="fullscreen">Fullscreen state.</param>
+        public static unsafe void MarkFullscreen(IntPtr hwnd, bool fullscreen)
+        {
+            if (s_taskBarList == IntPtr.Zero)
+            {
+                Guid clsid = ShellIds.TaskBarList;
+                Guid iid = ShellIds.ITaskBarList2;
+
+                int result = CoCreateInstance(ref clsid, IntPtr.Zero, 1, ref iid, out s_taskBarList);
+
+                if (s_taskBarList != IntPtr.Zero)
+                {
+                    var ptr = (ITaskBarList2VTable**)s_taskBarList.ToPointer();
+
+                    if (s_hrInitDelegate is null)
+                    {
+                        s_hrInitDelegate = Marshal.GetDelegateForFunctionPointer<HrInit>((*ptr)->HrInit);
+                    }
+
+                    if (s_hrInitDelegate(s_taskBarList) != HRESULT.S_OK)
+                    {
+                        s_taskBarList = IntPtr.Zero;
+                    }
+                }
+            }
+
+            if (s_taskBarList != IntPtr.Zero)
+            {
+                var ptr = (ITaskBarList2VTable**)s_taskBarList.ToPointer();
+
+                if (s_markFullscreenWindowDelegate is null)
+                {
+                    s_markFullscreenWindowDelegate = Marshal.GetDelegateForFunctionPointer<MarkFullscreenWindow>((*ptr)->MarkFullscreenWindow);
+                }
+
+                s_markFullscreenWindowDelegate(s_taskBarList, hwnd, fullscreen);
+            }
+        }
+    }
+}

src/Windows/Avalonia.Win32/Interop/UnmanagedMethods.cs

@@ -1880,6 +1880,22 @@ namespace Avalonia.Win32.Interop
             [MarshalAs(UnmanagedType.LPWStr)]
             public string pszSpec;
         }
+
+        public delegate void MarkFullscreenWindow(IntPtr This, IntPtr hwnd, [MarshalAs(UnmanagedType.Bool)] bool fullscreen);
+        public delegate HRESULT HrInit(IntPtr This);
+
+        public struct ITaskBarList2VTable
+        {
+            public IntPtr IUnknown1;
+            public IntPtr IUnknown2;
+            public IntPtr IUnknown3;
+            public IntPtr HrInit;
+            public IntPtr AddTab;
+            public IntPtr DeleteTab;
+            public IntPtr ActivateTab;
+            public IntPtr SetActiveAlt;
+            public IntPtr MarkFullscreenWindow;
+        }
     }
 
     [Flags]

src/Windows/Avalonia.Win32/WindowImpl.cs

@@ -39,7 +39,6 @@ namespace Avalonia.Win32
 
         private SavedWindowInfo _savedWindowInfo;
         private bool _isFullScreenActive;
-        private IntPtr _taskBarList;
 
 #if USE_MANAGED_DRAG
         private readonly ManagedWindowResizeDragHelper _managedDrag;
@@ -545,40 +544,6 @@ namespace Avalonia.Win32
             }
         }
 
-        /// <summary>
-        /// Ported from https://github.com/chromium/chromium/blob/master/ui/views/win/fullscreen_handler.cc
-        /// </summary>
-        /// <param name="fullscreen">Fullscreen state.</param>
-        private unsafe void MarkFullscreen(bool fullscreen)
-        {
-            if (_taskBarList == IntPtr.Zero)
-            {
-                Guid clsid = ShellIds.TaskBarList;
-                Guid iid = ShellIds.ITaskBarList2;
-
-                int result = CoCreateInstance(ref clsid, IntPtr.Zero, 1, ref iid, out _taskBarList);
-
-                if (_taskBarList != IntPtr.Zero)
-                {
-                    var ptr = (ITaskBarList2VTable**)_taskBarList.ToPointer();
-
-                    var hrInit = Marshal.GetDelegateForFunctionPointer<HrInit>((*ptr)->HrInit);
-
-                    if (hrInit(_taskBarList) != HRESULT.S_OK)
-                    {
-                        _taskBarList = IntPtr.Zero;
-                    }
-                }
-            }
-
-            if (_taskBarList != IntPtr.Zero)
-            {
-                var ptr = (ITaskBarList2VTable**)_taskBarList.ToPointer();
-                var markFullscreen = Marshal.GetDelegateForFunctionPointer<MarkFullscreenWindow>((*ptr)->MarkFullscreenWindow);
-                markFullscreen(_taskBarList, _hwnd, fullscreen);
-            }
-        }
-
         /// <summary>
         /// Ported from https://github.com/chromium/chromium/blob/master/ui/views/win/fullscreen_handler.cc
         /// Method must only be called from inside UpdateWindowProperties.
@@ -634,7 +599,7 @@ namespace Avalonia.Win32
                 UpdateWindowProperties(_windowProperties, true);
             }
 
-            MarkFullscreen(fullscreen);
+            TaskBarList.MarkFullscreen(_hwnd, fullscreen);
         }
 
         private void ShowWindow(WindowState state)