Merge pull request #4555 from MahApps/fix/4554-window-not-movable

Use WindowInteropHelper to get the window handle

Author: punker76

src/MahApps.Metro/Controls/MetroWindow.cs

@@ -1,4 +1,4 @@
-// Licensed to the .NET Foundation under one or more agreements.
+// Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
@@ -7,7 +7,6 @@
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Linq;
-using System.Reflection;
 using System.Windows;
 using System.Windows.Automation;
 using System.Windows.Automation.Peers;
@@ -18,6 +17,7 @@
 using System.Windows.Shapes;
 using System.Windows.Controls.Primitives;
 using System.Windows.Data;
+using System.Windows.Interop;
 using ControlzEx.Behaviors;
 using ControlzEx.Native;
 using ControlzEx.Standard;
@@ -1279,16 +1279,6 @@ protected override AutomationPeer OnCreateAutomationPeer()
             return new MetroWindowAutomationPeer(this);
         }
 
-        protected internal IntPtr CriticalHandle
-        {
-            get
-            {
-                this.VerifyAccess();
-                var value = typeof(Window).GetProperty("CriticalHandle", BindingFlags.NonPublic | BindingFlags.Instance)?.GetValue(this, new object[0]) ?? IntPtr.Zero;
-                return (IntPtr)value;
-            }
-        }
-
         private void ClearWindowEvents()
         {
             // clear all event handlers first:
@@ -1470,7 +1460,6 @@ internal static void DoWindowTitleThumbMoveOnDragDelta(IMetroThumb thumb, [NotNu
                 window.StateChanged += windowOnStateChanged;
             }
 
-            var criticalHandle = window.CriticalHandle;
 #pragma warning disable 618
             // these lines are from DragMove
             // NativeMethods.SendMessage(criticalHandle, WM.SYSCOMMAND, (IntPtr)SC.MOUSEMOVE, IntPtr.Zero);
@@ -1479,7 +1468,8 @@ internal static void DoWindowTitleThumbMoveOnDragDelta(IMetroThumb thumb, [NotNu
             var wpfPoint = window.PointToScreen(Mouse.GetPosition(window));
             var x = (int)wpfPoint.X;
             var y = (int)wpfPoint.Y;
-            NativeMethods.SendMessage(criticalHandle, WM.NCLBUTTONDOWN, (IntPtr)HT.CAPTION, new IntPtr(x | (y << 16)));
+            var windowHandle = new WindowInteropHelper(window).EnsureHandle();
+            NativeMethods.SendMessage(windowHandle, WM.NCLBUTTONDOWN, (IntPtr)HT.CAPTION, new IntPtr(x | (y << 16)));
 #pragma warning restore 618
         }