Fix: Fixed crashes when using the Preview Pane (#18200)

Author: workbysaran

src/Files.App/ViewModels/UserControls/Previews/ShellPreviewViewModel.cs

@@ -34,6 +34,7 @@ public sealed partial class ShellPreviewViewModel : BasePreviewModel
 		WNDPROC _windProc = null!;
 		HWND _hWnd = HWND.Null;
 		bool _isOfficePreview = false;
+		unsafe char* _pszClassName;
 
 		// Constructor
 
@@ -136,42 +137,41 @@ public unsafe void LoadPreview(UIElement presenter)
 			var szClassName = $"{nameof(ShellPreviewViewModel)}-{Guid.NewGuid()}";
 			var szWindowName = $"Preview";
 
-			fixed (char* pszClassName = szClassName)
-			{
-				_windProc = new(WndProc);
-				var pWindProc = Marshal.GetFunctionPointerForDelegate(_windProc);
-				var pfnWndProc = (delegate* unmanaged[Stdcall]<HWND, uint, WPARAM, LPARAM, LRESULT>)pWindProc;
+			_pszClassName = (char*)Marshal.StringToHGlobalUni(szClassName);
 
-				_windowClass = new WNDCLASSEXW()
-				{
-					cbSize = (uint)sizeof(WNDCLASSEXW),
-					lpfnWndProc = pfnWndProc,
-					hInstance = hInst,
-					lpszClassName = pszClassName,
-					style = 0,
-					hIcon = default,
-					hIconSm = default,
-					hCursor = default,
-					hbrBackground = default,
-					lpszMenuName = null,
-					cbClsExtra = 0,
-					cbWndExtra = 0,
-				};
-
-				PInvoke.RegisterClassEx(_windowClass);
-
-				fixed (char* pszWindowName = szWindowName)
-				{
-					_hWnd = PInvoke.CreateWindowEx(
-						WINDOW_EX_STYLE.WS_EX_LAYERED | WINDOW_EX_STYLE.WS_EX_COMPOSITED,
-						pszClassName,
-						pszWindowName,
-						WINDOW_STYLE.WS_CHILD | WINDOW_STYLE.WS_CLIPSIBLINGS | WINDOW_STYLE.WS_VISIBLE,
-						0, 0, 0, 0,
-						new(parent),
-						HMENU.Null,
-						hInst);
-				}
+			_windProc = new(WndProc);
+			var pWindProc = Marshal.GetFunctionPointerForDelegate(_windProc);
+			var pfnWndProc = (delegate* unmanaged[Stdcall]<HWND, uint, WPARAM, LPARAM, LRESULT>)pWindProc;
+
+			_windowClass = new WNDCLASSEXW()
+			{
+				cbSize = (uint)sizeof(WNDCLASSEXW),
+				lpfnWndProc = pfnWndProc,
+				hInstance = hInst,
+				lpszClassName = _pszClassName,
+				style = 0,
+				hIcon = default,
+				hIconSm = default,
+				hCursor = default,
+				hbrBackground = default,
+				lpszMenuName = null,
+				cbClsExtra = 0,
+				cbWndExtra = 0,
+			};
+
+			PInvoke.RegisterClassEx(_windowClass);
+
+			fixed (char* pszWindowName = szWindowName)
+			{
+				_hWnd = PInvoke.CreateWindowEx(
+					WINDOW_EX_STYLE.WS_EX_LAYERED | WINDOW_EX_STYLE.WS_EX_COMPOSITED,
+					_pszClassName,
+					pszWindowName,
+					WINDOW_STYLE.WS_CHILD | WINDOW_STYLE.WS_CLIPSIBLINGS | WINDOW_STYLE.WS_VISIBLE,
+					0, 0, 0, 0,
+					new(parent),
+					HMENU.Null,
+					hInst);
 			}
 
 			_ = ChildWindowToXaml(parent, presenter);
@@ -252,7 +252,7 @@ private unsafe bool ChildWindowToXaml(nint parent, UIElement presenter)
 				.Succeeded;
 		}
 
-		public void UnloadPreview()
+		public unsafe void UnloadPreview()
 		{
 			if (_hWnd != HWND.Null)
 			{
@@ -267,6 +267,12 @@ public void UnloadPreview()
 			_contentExternalOutputLink = null;
 
 			PInvoke.UnregisterClass(_windowClass.lpszClassName, PInvoke.GetModuleHandle(default(PWSTR)));
+
+			if (_pszClassName is not null)
+			{
+				Marshal.FreeHGlobal((nint)_pszClassName);
+				_pszClassName = null;
+			}
 		}
 
 		public unsafe void PointerEntered(bool onPreview)