check window visibility state from WM_WINDOWPOSCHANGED message

Author: emmauss

src/Windows/Avalonia.Win32/WindowImpl.AppWndProc.cs

@@ -790,6 +790,17 @@ protected virtual unsafe IntPtr AppWndProc(IntPtr hWnd, uint msg, IntPtr wParam,
                         return UiaCoreProviderApi.UiaReturnRawElementProvider(_hwnd, wParam, lParam, node);
                     }
                     break;
+                case WindowsMessage.WM_WINDOWPOSCHANGED:
+                    var winPos = Marshal.PtrToStructure<WINDOWPOS>(lParam);
+                    if((winPos.flags & (uint)SetWindowPosFlags.SWP_SHOWWINDOW) != 0)
+                    {
+                        _shown = true;
+                    }
+                    else if ((winPos.flags & (uint)SetWindowPosFlags.SWP_HIDEWINDOW) != 0)
+                    {
+                        _shown = false;
+                    }
+                    break;
             }
 
 #if USE_MANAGED_DRAG

src/Windows/Avalonia.Win32/WindowImpl.cs

@@ -1203,11 +1203,6 @@ private void ShowWindow(WindowState state, bool activate)
             if (command.HasValue)
             {
                 UnmanagedMethods.ShowWindow(_hwnd, command.Value);
-
-                if (!_shown && command.Value != ShowWindowCommand.Minimize && GetStyle().HasFlag(WindowStyles.WS_VISIBLE))
-                {
-                    _shown = true;
-                }
             }
 
             if (state == WindowState.Maximized)