winui: extract parent window handling

Extract logic display a model window that is correctly parented to the
GCM_MODAL_PARENTHWND window handle.

Author: mjcheetham

src/windows/GitHub.UI.Windows/Program.cs

@@ -12,15 +12,7 @@ public static class Program
     {
         public static void Main(string[] args)
         {
-            IGui gui;
-            if (TryGetParentWindowHandle(out IntPtr parentHwnd))
-            {
-                gui = new Gui(parentHwnd);
-            }
-            else
-            {
-                gui = new Gui();
-            }
+            IGui gui = new Gui();
 
             try
             {
@@ -97,19 +89,5 @@ public static void Main(string[] args)
                 Environment.Exit(-1);
             }
         }
-
-        private static bool TryGetParentWindowHandle(out IntPtr hwnd)
-        {
-            string envar = Environment.GetEnvironmentVariable(Constants.EnvironmentVariables.GcmParentWindow);
-
-            if (long.TryParse(envar, out long ptrInt))
-            {
-                hwnd = new IntPtr(ptrInt);
-                return true;
-            }
-
-            hwnd = default(IntPtr);
-            return false;
-        }
     }
 }

src/windows/GitHub.UI.Windows/Tester.xaml.cs

@@ -23,12 +23,18 @@ public Tester()
 
         private void ShowCredentials(object sender, RoutedEventArgs e)
         {
-            new GitHubDialogWindow(new LoginCredentialsViewModel(true, true), new LoginCredentialsView()).ShowDialog(Handle);
+            var model = new LoginCredentialsViewModel(true, true);
+            var view = new LoginCredentialsView();
+            var window = new GitHubDialogWindow(model, view);
+            Gui.ShowDialog(window, Handle);
         }
 
         private void ShowAuthenticationCode(object sender, RoutedEventArgs e)
         {
-            new GitHubDialogWindow(new Login2FaViewModel(TwoFactorType.AuthenticatorApp), new Login2FaView()).ShowDialog(Handle);
+            var model = new Login2FaViewModel(TwoFactorType.AuthenticatorApp);
+            var view = new Login2FaView();
+            var window = new GitHubDialogWindow(model, view);
+            Gui.ShowDialog(window, Handle);
         }
     }
 }

src/windows/Shared.UI.Windows/Gui.cs

@@ -30,16 +30,16 @@ public interface IGui
 
     public class Gui : IGui
     {
-        private readonly IntPtr? _parentHwnd;
+        private readonly IntPtr _parentHwnd = IntPtr.Zero;
 
         public Gui()
         {
-            _parentHwnd = null;
-        }
+            string envar = Environment.GetEnvironmentVariable(Constants.EnvironmentVariables.GcmParentWindow);
 
-        public Gui(IntPtr parentHwnd)
-        {
-            _parentHwnd = parentHwnd;
+            if (long.TryParse(envar, out long ptrInt))
+            {
+                _parentHwnd = new IntPtr(ptrInt);
+            }
         }
 
         public bool ShowDialogWindow(Func<Window> windowCreator)
@@ -50,7 +50,7 @@ public bool ShowDialogWindow(Func<Window> windowCreator)
             {
                 var window = windowCreator();
 
-                windowResult = window.ShowDialog(_parentHwnd) ?? false;
+                windowResult = ShowDialog(window, _parentHwnd) ?? false;
             })
             .Wait();
 
@@ -67,7 +67,7 @@ public bool ShowViewModel(ViewModel viewModel, Func<Window> windowCreator)
 
                 window.DataContext = viewModel;
 
-                windowResult = window.ShowDialog(_parentHwnd) ?? false;
+                windowResult = ShowDialog(window, _parentHwnd) ?? false;
             })
             .Wait();
 
@@ -95,25 +95,17 @@ private static Task StartSTATask(Action action)
 
             return completionSource.Task;
         }
-    }
-
-    public static class WindowExtensions
-    {
-        public static void SetOwnerHandle(this Window window, IntPtr hwnd)
-        {
-            new System.Windows.Interop.WindowInteropHelper(window).Owner = hwnd;
-        }
 
-        public static bool? ShowDialog(this Window window, IntPtr? parentHwnd)
+        public static bool? ShowDialog(Window window, IntPtr parentHwnd)
         {
             // Zero is not a valid window handles
-            if (!parentHwnd.HasValue || parentHwnd.Value == IntPtr.Zero)
+            if (parentHwnd == IntPtr.Zero)
             {
                 return window.ShowDialog();
             }
 
             // Set the parent window handle and ensure the dialog starts in the correct location
-            window.SetOwnerHandle(parentHwnd.Value);
+            new System.Windows.Interop.WindowInteropHelper(window).Owner = parentHwnd;
             window.WindowStartupLocation = WindowStartupLocation.CenterOwner;
 
             const int ERROR_INVALID_WINDOW_HANDLE = 1400;