Added TopLevel::BeginMoveDrag()

src/Android/Perspex.Android/Platform/SkiaPlatform/WindowImpl.cs

@@ -126,6 +126,11 @@ namespace Perspex.Android.Platform.SkiaPlatform
             this.Visibility = ViewStates.Visible;
         }
 
+        public void BeginMoveDrag()
+        {
+            //Not supported
+        }
+
         public IDisposable ShowDialog()
         {
             throw new NotImplementedException();

src/Gtk/Perspex.Gtk/WindowImpl.cs

@@ -162,6 +162,14 @@ namespace Perspex.Gtk
             GdkWindow.Cursor = cursor != null ? new Gdk.Cursor(cursor.Handle) : DefaultCursor;
         }
 
+        public void BeginMoveDrag()
+        {
+            int x, y;
+            ModifierType mod;
+            Screen.RootWindow.GetPointer(out x, out y, out mod);
+            BeginMoveDrag(0, x, y, 0);
+        }
+
         public IDisposable ShowDialog()
         {
             Modal = true;

src/Perspex.Controls/Platform/ITopLevelImpl.cs

@@ -88,5 +88,10 @@ namespace Perspex.Platform
         /// Shows the toplevel.
         /// </summary>
         void Show();
+
+        /// <summary>
+        /// Starts moving a window with left button being held. Should be called from left mouse button press event handler
+        /// </summary>
+        void BeginMoveDrag();
     }
 }

src/Perspex.Controls/Platform/PlatformManager.cs

@@ -174,6 +174,7 @@ namespace Perspex.Controls.Platform
             public void SetTitle(string title) => _window.SetTitle(title);
 
             public void Show() => _tl.Show();
+            public void BeginMoveDrag() => _tl.BeginMoveDrag();
 
             public IDisposable ShowDialog() => _window.ShowDialog();
 

src/Perspex.Controls/TopLevel.cs

@@ -364,5 +364,10 @@ namespace Perspex.Controls
         {
             _renderQueueManager?.InvalidateRender(this);
         }
+
+        /// <summary>
+        /// Starts moving a window with left button being held. Should be called from left mouse button press event handler
+        /// </summary>
+        public void BeginMoveDrag() => PlatformImpl.BeginMoveDrag();
     }
 }

src/Windows/Perspex.Win32/WindowImpl.cs

@@ -223,6 +223,12 @@ namespace Perspex.Win32
             UnmanagedMethods.ShowWindow(_hwnd, UnmanagedMethods.ShowWindowCommand.Normal);
         }
 
+        public void BeginMoveDrag()
+        {
+            UnmanagedMethods.DefWindowProc(_hwnd, (int) UnmanagedMethods.WindowsMessage.WM_NCLBUTTONDOWN,
+                new IntPtr(2), IntPtr.Zero);
+        }
+
         public virtual IDisposable ShowDialog()
         {
             var disabled = s_instances.Where(x => x != this && x.IsEnabled).ToList();

src/iOS/Perspex.iOS/PerspexView.cs

@@ -107,6 +107,11 @@ namespace Perspex.iOS
             _keyboardHelper.ActivateAutoShowKeybord();
         }
 
+        public void BeginMoveDrag()
+        {
+            //Not supported
+        }
+
         public Size MaxClientSize => Bounds.Size.ToPerspex();
         public void SetTitle(string title)
         {