Merge pull request #4928 from MarchingCube/fix-win32-dialog-minimizing-parent

Fix closing dialog windows on win32 causing parent window to be moved to back

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

@@ -1017,6 +1017,9 @@ namespace Avalonia.Win32.Interop
         [DllImport("user32.dll")]
         public static extern bool ValidateRect(IntPtr hWnd, IntPtr lpRect);
 
+        [DllImport("user32.dll")]
+        public static extern bool IsWindow(IntPtr hWnd);
+        
         [DllImport("user32.dll")]
         public static extern bool IsWindowEnabled(IntPtr hWnd);
 
@@ -1050,6 +1053,9 @@ namespace Avalonia.Win32.Interop
         [DllImport("user32.dll")]
         public static extern bool ScreenToClient(IntPtr hWnd, ref POINT lpPoint);
 
+        [DllImport("user32.dll", SetLastError = true)]
+        public static extern IntPtr GetActiveWindow();
+        
         [DllImport("user32.dll", SetLastError = true)]
         public static extern IntPtr SetActiveWindow(IntPtr hWnd);
 

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

@@ -65,6 +65,24 @@ namespace Avalonia.Win32
                             return IntPtr.Zero;
                         }
 
+                        // Based on https://github.com/dotnet/wpf/blob/master/src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Window.cs#L4270-L4337
+                        // We need to enable parent window before destroying child window to prevent OS from activating a random window behind us.
+                        // This is described here: https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-enablewindow#remarks
+                        // Our window closed callback will set enabled state to a correct value after child window gets destroyed.
+                        // We need to verify if parent is still alive (perhaps it got destroyed somehow).
+                        if (_parent != null && IsWindow(_parent._hwnd))
+                        {
+                            var wasActive = GetActiveWindow() == _hwnd;
+
+                            _parent.SetEnabled(true);
+
+                            // We also need to activate our parent window since again OS might try to activate a window behind if it is not set.
+                            if (wasActive)
+                            {
+                                SetActiveWindow(_parent._hwnd);
+                            }
+                        }
+
                         break;
                     }