wpf: readd WPF UI/threading helpers

Author: mjcheetham

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

@@ -0,0 +1,93 @@
+using System;
+using System.ComponentModel;
+using System.Threading;
+using System.Threading.Tasks;
+using System.Windows;
+using System.Windows.Controls;
+using Microsoft.Git.CredentialManager.UI.Controls;
+using Microsoft.Git.CredentialManager.UI.ViewModels;
+
+namespace Microsoft.Git.CredentialManager.UI
+{
+    public static class Gui
+    {
+        /// <summary>
+        /// Present the user with a <see cref="Window"/>.
+        /// </summary>
+        /// <param name="windowCreator"><see cref="Window"/> factory.</param>
+        /// <param name="parentHwnd">Parent window handle.</param>
+        /// <returns>
+        /// Returns `<see langword="true"/>` if the user completed the dialog; otherwise `<see langword="false"/>`
+        /// if the user canceled or abandoned the dialog.
+        /// </returns>
+        public static Task ShowWindow(Func<Window> windowCreator, IntPtr parentHwnd)
+        {
+            return StartSTATask(() => ShowDialog(windowCreator(), parentHwnd));
+        }
+
+        /// <summary>
+        /// Present the user with a <see cref="DialogWindow"/>.
+        /// </summary>
+        /// <returns>
+        /// Returns `<see langword="true"/>` if the user completed the dialog and the view model is valid;
+        /// otherwise `<see langword="false"/>` if the user canceled or abandoned the dialog, or the view
+        /// model is invalid.
+        /// </returns>
+        /// <param name="viewModel">Window view model.</param>
+        /// <param name="contentCreator">Window content factory.</param>
+        /// <param name="parentHwnd">Parent window handle.</param>
+        public static Task ShowDialogWindow(WindowViewModel viewModel, Func<UserControl> contentCreator, IntPtr parentHwnd)
+        {
+            return ShowWindow(() => new DialogWindow(contentCreator()) { DataContext = viewModel }, parentHwnd);
+        }
+
+        private static Task StartSTATask(Action action)
+        {
+            var completionSource = new TaskCompletionSource<object>();
+            var thread = new Thread(() =>
+            {
+                try
+                {
+                    action();
+                    completionSource.SetResult(null);
+                }
+                catch (Exception e)
+                {
+                    completionSource.SetException(e);
+                }
+            });
+
+            thread.SetApartmentState(ApartmentState.STA);
+            thread.Start();
+
+            return completionSource.Task;
+        }
+
+        public static bool? ShowDialog(Window window, IntPtr parentHwnd)
+        {
+            // Zero is not a valid window handle
+            if (parentHwnd == IntPtr.Zero)
+            {
+                return window.ShowDialog();
+            }
+
+            // Set the parent window handle and ensure the dialog starts in the correct location
+            new System.Windows.Interop.WindowInteropHelper(window).Owner = parentHwnd;
+            window.WindowStartupLocation = WindowStartupLocation.CenterOwner;
+
+            const int ERROR_INVALID_WINDOW_HANDLE = 1400;
+
+            try
+            {
+                return window.ShowDialog();
+            }
+            catch (Win32Exception ex) when (ex.NativeErrorCode == ERROR_INVALID_WINDOW_HANDLE)
+            {
+                // The window handle given was invalid - clear the owner and show the dialog centered on the screen
+                window.Owner = null;
+                window.WindowStartupLocation = WindowStartupLocation.CenterScreen;
+                return window.ShowDialog();
+            }
+        }
+    }
+}