[RegistryPreview]Fix showing in the background on start (#28452)

* [RegistryPreview] Fix showing in the background on start

* Use existing window handle

src/common/ManagedCommon/NativeMethods.cs

@@ -26,5 +26,17 @@ namespace ManagedCommon
 
         [DllImport("kernel32.dll", SetLastError = true)]
         internal static extern bool CloseHandle(IntPtr hObject);
+
+        [DllImport("user32.dll", SetLastError = true)]
+        internal static extern IntPtr SetForegroundWindow(IntPtr hWnd);
+
+        [DllImport("user32.dll")]
+        internal static extern IntPtr GetForegroundWindow();
+
+        [DllImport("user32.dll")]
+        internal static extern uint GetWindowThreadProcessId(IntPtr hWnd, IntPtr processId);
+
+        [DllImport("user32.dll")]
+        internal static extern bool AttachThreadInput(uint idAttach, uint idAttachTo, bool fAttach);
     }
 }

src/common/ManagedCommon/WindowHelpers.cs

@@ -0,0 +1,30 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+
+namespace ManagedCommon
+{
+    public class WindowHelpers
+    {
+        public static void BringToForeground(IntPtr handle)
+        {
+            var fgHandle = NativeMethods.GetForegroundWindow();
+
+            var threadId1 = NativeMethods.GetWindowThreadProcessId(handle, System.IntPtr.Zero);
+            var threadId2 = NativeMethods.GetWindowThreadProcessId(fgHandle, System.IntPtr.Zero);
+
+            if (threadId1 != threadId2)
+            {
+                NativeMethods.AttachThreadInput(threadId1, threadId2, true);
+                NativeMethods.SetForegroundWindow(handle);
+                NativeMethods.AttachThreadInput(threadId1, threadId2, false);
+            }
+            else
+            {
+                NativeMethods.SetForegroundWindow(handle);
+            }
+        }
+    }
+}

src/modules/Hosts/Hosts/Helpers/NativeMethods.cs

@@ -1,24 +0,0 @@
-// Copyright (c) Microsoft Corporation
-// The Microsoft Corporation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-using System;
-using System.Runtime.InteropServices;
-
-namespace Hosts.Helpers
-{
-    internal sealed class NativeMethods
-    {
-        [DllImport("user32.dll", SetLastError = true)]
-        internal static extern IntPtr SetForegroundWindow(IntPtr hWnd);
-
-        [DllImport("user32.dll")]
-        internal static extern IntPtr GetForegroundWindow();
-
-        [DllImport("user32.dll")]
-        internal static extern uint GetWindowThreadProcessId(IntPtr hWnd, IntPtr processId);
-
-        [DllImport("user32.dll")]
-        internal static extern bool AttachThreadInput(uint idAttach, uint idAttachTo, bool fAttach);
-    }
-}

src/modules/Hosts/Hosts/HostsXAML/MainWindow.xaml.cs

@@ -24,7 +24,8 @@ namespace Hosts
             Title = title;
             AppTitleTextBlock.Text = title;
 
-            BringToForeground();
+            var handle = this.GetWindowHandle();
+            ManagedCommon.WindowHelpers.BringToForeground(handle);
 
             Activated += MainWindow_Activated;
         }
@@ -40,25 +41,5 @@ namespace Hosts
                 AppTitleTextBlock.Foreground = (SolidColorBrush)App.Current.Resources["WindowCaptionForeground"];
             }
         }
-
-        private void BringToForeground()
-        {
-            var handle = this.GetWindowHandle();
-            var fgHandle = NativeMethods.GetForegroundWindow();
-
-            var threadId1 = NativeMethods.GetWindowThreadProcessId(handle, System.IntPtr.Zero);
-            var threadId2 = NativeMethods.GetWindowThreadProcessId(fgHandle, System.IntPtr.Zero);
-
-            if (threadId1 != threadId2)
-            {
-                NativeMethods.AttachThreadInput(threadId1, threadId2, true);
-                NativeMethods.SetForegroundWindow(handle);
-                NativeMethods.AttachThreadInput(threadId1, threadId2, false);
-            }
-            else
-            {
-                NativeMethods.SetForegroundWindow(handle);
-            }
-        }
     }
 }

src/modules/registrypreview/RegistryPreviewUI/RegistryPreviewXAML/MainWindow.xaml.cs

@@ -97,6 +97,8 @@ namespace RegistryPreview
                 UpdateToolBarAndUI(false);
                 UpdateWindowTitle(resourceLoader.GetString("FileNotFound"));
             }
+
+            ManagedCommon.WindowHelpers.BringToForeground(windowHandle);
         }
 
         private void MainWindow_Activated(object sender, WindowActivatedEventArgs args)