diff --git a/packages.cake b/packages.cake
index 84a04b7238..7ffc805ec8 100644
--- a/packages.cake
+++ b/packages.cake
@@ -120,6 +120,7 @@ public class Packages
         var SharpDXDirect3D9Version = packageVersions["SharpDX.Direct3D9"].FirstOrDefault().Item1;
         var SharpDXDXGIVersion = packageVersions["SharpDX.DXGI"].FirstOrDefault().Item1;
         var SystemMemoryVersion = packageVersions["System.Memory"].FirstOrDefault().Item1;
+        var SystemComponentModelAnnotationsVersion = packageVersions["System.ComponentModel.Annotations"].FirstOrDefault().Item1;
 
         context.Information("Package: Serilog, version: {0}", SerilogVersion);
         context.Information("Package: System.Reactive, version: {0}", SystemReactiveVersion);
@@ -238,6 +239,7 @@ public class Packages
                     new NuSpecDependency() { Id = "System.Reactive", Version = SystemReactiveVersion },
                     new NuSpecDependency() { Id = "Avalonia.Remote.Protocol", Version = parameters.Version },
                     new NuSpecDependency() { Id = "System.Memory", Version = SystemMemoryVersion },
+                    new NuSpecDependency() { Id = "System.ComponentModel.Annotations", Version = SystemComponentModelAnnotationsVersion },
                     //.NET Core
                     new NuSpecDependency() { Id = "System.Threading.ThreadPool", TargetFramework = "netcoreapp2.0", Version = "4.3.0" },
                     new NuSpecDependency() { Id = "Microsoft.Extensions.DependencyModel", TargetFramework = "netcoreapp2.0", Version = "1.1.0" },
diff --git a/readme.md b/readme.md
index 2b26cbdd1a..4fe76a2faf 100644
--- a/readme.md
+++ b/readme.md
@@ -18,7 +18,7 @@ Avalonia is a WPF-inspired cross-platform XAML-based UI framework providing a fl
 
 ## Getting Started
 
-Avalonia [Visual Studio Extension](https://marketplace.visualstudio.com/items?itemName=AvaloniaTeam.AvaloniaforVisualStudio) contains project and control templates that will help you get started. After installing it, open "New Project" dialog in Visual Studio, choose "Avalonia" in "Visual C#" section, select "Avalonia .NET Core Application" and press OK (<a href="http://avaloniaui.net/tutorial/images/add-dialogs.png">screenshot</a>). Now you can write code and markup that will work on multiple platforms!
+Avalonia [Visual Studio Extension](https://marketplace.visualstudio.com/items?itemName=AvaloniaTeam.AvaloniaforVisualStudio) contains project and control templates that will help you get started. After installing it, open "New Project" dialog in Visual Studio, choose "Avalonia" in "Visual C#" section, select "Avalonia .NET Core Application" and press OK (<a href="http://avaloniaui.net/docs/quickstart/images/new-project-dialog.png">screenshot</a>). Now you can write code and markup that will work on multiple platforms!
 
 Avalonia is delivered via <b>NuGet</b> package manager. You can find the packages here: ([stable(ish)](https://www.nuget.org/packages/Avalonia/), [nightly](https://github.com/AvaloniaUI/Avalonia/wiki/Using-nightly-build-feed))
 
@@ -52,7 +52,7 @@ Please read the [contribution guidelines](http://avaloniaui.net/contributing/con
 ### Contributors
 
 This project exists thanks to all the people who contribute. [[Contribute](http://avaloniaui.net/contributing/contributing)].
-<a href="graphs/contributors"><img src="https://opencollective.com/Avalonia/contributors.svg?width=890&button=false" /></a>
+<a href="https://github.com/AvaloniaUI/Avalonia/graphs/contributors"><img src="https://opencollective.com/Avalonia/contributors.svg?width=890&button=false" /></a>
 
 
 ### Backers
diff --git a/samples/ControlCatalog/DecoratedWindow.xaml.cs b/samples/ControlCatalog/DecoratedWindow.xaml.cs
index d28281e476..749f83c1ab 100644
--- a/samples/ControlCatalog/DecoratedWindow.xaml.cs
+++ b/samples/ControlCatalog/DecoratedWindow.xaml.cs
@@ -20,7 +20,7 @@ namespace ControlCatalog
             ctl.Cursor = new Cursor(cursor);
             ctl.PointerPressed += delegate
             {
-                PlatformImpl.BeginResizeDrag(edge);
+                PlatformImpl?.BeginResizeDrag(edge);
             };
         }
 
@@ -29,7 +29,7 @@ namespace ControlCatalog
             AvaloniaXamlLoader.Load(this);
             this.FindControl<Control>("TitleBar").PointerPressed += delegate
             {
-                PlatformImpl.BeginMoveDrag();
+                PlatformImpl?.BeginMoveDrag();
             };
             SetupSide("Left", StandardCursorType.LeftSide, WindowEdge.West);
             SetupSide("Right", StandardCursorType.RightSide, WindowEdge.East);
diff --git a/src/Avalonia.Controls/AutoCompleteBox.cs b/src/Avalonia.Controls/AutoCompleteBox.cs
index 351cbf5520..96fb9be8ac 100644
--- a/src/Avalonia.Controls/AutoCompleteBox.cs
+++ b/src/Avalonia.Controls/AutoCompleteBox.cs
@@ -2150,7 +2150,7 @@ namespace Avalonia.Controls
             }
 
             // Update the view
-            if (e.Action == NotifyCollectionChangedAction.Remove || e.Action == NotifyCollectionChangedAction.Replace)
+            if ((e.Action == NotifyCollectionChangedAction.Remove || e.Action == NotifyCollectionChangedAction.Replace) && e.OldItems != null)
             {
                 for (int index = 0; index < e.OldItems.Count; index++)
                 {
diff --git a/src/Avalonia.Controls/Calendar/Calendar.cs b/src/Avalonia.Controls/Calendar/Calendar.cs
index 59281c5ad0..029e4dadc8 100644
--- a/src/Avalonia.Controls/Calendar/Calendar.cs
+++ b/src/Avalonia.Controls/Calendar/Calendar.cs
@@ -769,7 +769,7 @@ namespace Avalonia.Controls
         }
         private static void UpdateDisplayDate(Calendar c, DateTime addedDate, DateTime removedDate)
         {
-            Debug.Assert(c != null, "c should not be null!");
+            Contract.Requires<ArgumentNullException>(c != null);
 
             // If DisplayDate < DisplayDateStart, DisplayDate = DisplayDateStart
             if (DateTime.Compare(addedDate, c.DisplayDateRangeStart) < 0)
@@ -1016,8 +1016,6 @@ namespace Avalonia.Controls
 
         internal CalendarDayButton FindDayButtonFromDay(DateTime day)
         {
-            CalendarDayButton b;
-            DateTime? d;
             CalendarItem monthControl = MonthControl;
 
             // REMOVE_RTM: should be updated if we support MultiCalendar
@@ -1028,14 +1026,16 @@ namespace Avalonia.Controls
                 {
                     for (int childIndex = ColumnsPerMonth; childIndex < count; childIndex++)
                     {
-                        b = monthControl.MonthView.Children[childIndex] as CalendarDayButton;
-                        d = b.DataContext as DateTime?;
-
-                        if (d.HasValue)
+                        if (monthControl.MonthView.Children[childIndex] is CalendarDayButton b)
                         {
-                            if (DateTimeHelper.CompareDays(d.Value, day) == 0)
+                            var d = b.DataContext as DateTime?;
+
+                            if (d.HasValue)
                             {
-                                return b;
+                                if (DateTimeHelper.CompareDays(d.Value, day) == 0)
+                                {
+                                    return b;
+                                }
                             }
                         }
                     }
@@ -1044,20 +1044,6 @@ namespace Avalonia.Controls
             return null;
         }
 
-        private void Calendar_SizeChanged(object sender, EventArgs e)
-        {
-            Debug.Assert(sender is Calendar, "The sender should be a Calendar!");
-
-            var size = Bounds.Size;
-            RectangleGeometry rg = new RectangleGeometry();
-            rg.Rect = new Rect(0, 0, size.Width, size.Height);
-
-            if (Root != null)
-            {
-                Root.Clip = rg;
-            }
-        }
-
         private void OnSelectedMonthChanged(DateTime? selectedMonth)
         {
             if (selectedMonth.HasValue)
@@ -1090,7 +1076,6 @@ namespace Avalonia.Controls
 
         internal void ResetStates()
         {
-            CalendarDayButton d;
             CalendarItem monthControl = MonthControl;
             int count = RowsPerMonth * ColumnsPerMonth;
             if (monthControl != null)
@@ -1099,7 +1084,7 @@ namespace Avalonia.Controls
                 {
                     for (int childIndex = ColumnsPerMonth; childIndex < count; childIndex++)
                     {
-                        d = monthControl.MonthView.Children[childIndex] as CalendarDayButton;
+                        var d = (CalendarDayButton)monthControl.MonthView.Children[childIndex];
                         d.IgnoreMouseOverState();
                     }
                 }
@@ -1190,8 +1175,6 @@ namespace Avalonia.Controls
             if (HoverEnd != null && HoverStart != null)
             {
                 int startIndex, endIndex, i;
-                CalendarDayButton b;
-                DateTime? d;
                 CalendarItem monthControl = MonthControl;
 
                 // This assumes a contiguous set of dates:
@@ -1201,18 +1184,20 @@ namespace Avalonia.Controls
 
                     for (i = startIndex; i <= endIndex; i++)
                     {
-                        b = monthControl.MonthView.Children[i] as CalendarDayButton;
-                        b.IsSelected = true;
-                        d = b.DataContext as DateTime?;
-
-                        if (d.HasValue && DateTimeHelper.CompareDays(HoverEnd.Value, d.Value) == 0)
+                        if (monthControl.MonthView.Children[i] is CalendarDayButton b)
                         {
-                            if (FocusButton != null)
+                            b.IsSelected = true;
+                            var d = b.DataContext as DateTime?;
+
+                            if (d.HasValue && DateTimeHelper.CompareDays(HoverEnd.Value, d.Value) == 0)
                             {
-                                FocusButton.IsCurrent = false;
+                                if (FocusButton != null)
+                                {
+                                    FocusButton.IsCurrent = false;
+                                }
+                                b.IsCurrent = HasFocusInternal;
+                                FocusButton = b;
                             }
-                            b.IsCurrent = HasFocusInternal;
-                            FocusButton = b;
                         }
                     }
                 }
@@ -1228,8 +1213,6 @@ namespace Avalonia.Controls
             if (HoverEnd != null && HoverStart != null)
             {
                 CalendarItem monthControl = MonthControl;
-                CalendarDayButton b;
-                DateTime? d;
 
                 if (HoverEndIndex != null && HoverStartIndex != null)
                 {
@@ -1240,15 +1223,17 @@ namespace Avalonia.Controls
                     {
                         for (i = startIndex; i <= endIndex; i++)
                         {
-                            b = monthControl.MonthView.Children[i] as CalendarDayButton;
-                            d = b.DataContext as DateTime?;
-
-                            if (d.HasValue)
+                            if (monthControl.MonthView.Children[i] is CalendarDayButton b)
                             {
-                                if (!SelectedDates.Contains(d.Value))
+                                var d = b.DataContext as DateTime?;
+
+                                if (d.HasValue)
                                 {
-                                    b.IsSelected = false;
-                                }
+                                    if (!SelectedDates.Contains(d.Value))
+                                    {
+                                        b.IsSelected = false;
+                                    }
+                                } 
                             }
                         }
                     }
@@ -1257,7 +1242,7 @@ namespace Avalonia.Controls
                         // It is SingleRange
                         for (i = startIndex; i <= endIndex; i++)
                         {
-                            (monthControl.MonthView.Children[i] as CalendarDayButton).IsSelected = false;
+                            ((CalendarDayButton)monthControl.MonthView.Children[i]).IsSelected = false;
                         }
                     }
                 }
@@ -1628,16 +1613,15 @@ namespace Avalonia.Controls
                 e.Handled = true;
             }
         }
-        internal void Calendar_KeyDown(object sender, KeyEventArgs e)
-        {
-            Calendar c = sender as Calendar;
-            Debug.Assert(c != null, "c should not be null!");
 
-            if (!e.Handled && c.IsEnabled)
+        internal void Calendar_KeyDown(KeyEventArgs e)
+        {
+            if (!e.Handled && IsEnabled)
             {
                 e.Handled = ProcessCalendarKey(e);
             }
         }
+
         internal bool ProcessCalendarKey(KeyEventArgs e)
         {
             if (DisplayMode == CalendarMode.Month)
@@ -1976,7 +1960,7 @@ namespace Avalonia.Controls
                     }
             }
         }
-        private void Calendar_KeyUp(object sender, KeyEventArgs e)
+        private void Calendar_KeyUp(KeyEventArgs e)
         {
             if (!e.Handled && (e.Key == Key.LeftShift || e.Key == Key.RightShift))
             {
@@ -2083,6 +2067,9 @@ namespace Avalonia.Controls
             DisplayDateProperty.Changed.AddClassHandler<Calendar>(x => x.OnDisplayDateChanged);
             DisplayDateStartProperty.Changed.AddClassHandler<Calendar>(x => x.OnDisplayDateStartChanged);
             DisplayDateEndProperty.Changed.AddClassHandler<Calendar>(x => x.OnDisplayDateEndChanged);
+            KeyDownEvent.AddClassHandler<Calendar>(x => x.Calendar_KeyDown);
+            KeyUpEvent.AddClassHandler<Calendar>(x => x.Calendar_KeyUp);
+            
         }
 
         /// <summary>
@@ -2122,10 +2109,6 @@ namespace Avalonia.Controls
                     month.Owner = this;
                 }
             }
-
-            LayoutUpdated += Calendar_SizeChanged;
-            KeyDown += Calendar_KeyDown;
-            KeyUp += Calendar_KeyUp;
         }
 
     }
diff --git a/src/Avalonia.Controls/Calendar/CalendarDateRange.cs b/src/Avalonia.Controls/Calendar/CalendarDateRange.cs
index 273cda8c5b..718cc7142b 100644
--- a/src/Avalonia.Controls/Calendar/CalendarDateRange.cs
+++ b/src/Avalonia.Controls/Calendar/CalendarDateRange.cs
@@ -66,7 +66,7 @@ namespace Avalonia.Controls
         /// <returns>Inherited code: Requires comment 2.</returns>
         internal bool ContainsAny(CalendarDateRange range)
         {
-            Debug.Assert(range != null, "range should not be null!");
+            Contract.Requires<ArgumentNullException>(range != null);
 
             int start = DateTime.Compare(Start, range.Start);
 
diff --git a/src/Avalonia.Controls/Calendar/CalendarItem.cs b/src/Avalonia.Controls/Calendar/CalendarItem.cs
index 3432fa549d..b0cbd0be53 100644
--- a/src/Avalonia.Controls/Calendar/CalendarItem.cs
+++ b/src/Avalonia.Controls/Calendar/CalendarItem.cs
@@ -517,7 +517,7 @@ namespace Avalonia.Controls.Primitives
             for (int childIndex = Calendar.ColumnsPerMonth; childIndex < count; childIndex++)
             {
                 CalendarDayButton childButton = MonthView.Children[childIndex] as CalendarDayButton;
-                Debug.Assert(childButton != null, "childButton should not be null!");
+                Contract.Requires<ArgumentNullException>(childButton != null);
 
                 childButton.Index = childIndex;
                 SetButtonState(childButton, dateToAdd);
@@ -554,7 +554,7 @@ namespace Avalonia.Controls.Primitives
                     for (int i = childIndex; i < count; i++)
                     {
                         childButton = MonthView.Children[i] as CalendarDayButton;
-                        Debug.Assert(childButton != null, "childButton should not be null!");
+                        Contract.Requires<ArgumentNullException>(childButton != null);
                         // button needs a content to occupy the necessary space
                         // for the content presenter
                         childButton.Content = i.ToString(DateTimeHelper.GetCurrentDateFormat());
@@ -650,7 +650,7 @@ namespace Avalonia.Controls.Primitives
             foreach (object child in YearView.Children)
             {
                 CalendarButton childButton = child as CalendarButton;
-                Debug.Assert(childButton != null, "childButton should not be null!");
+                Contract.Requires<ArgumentNullException>(childButton != null);
                 // There should be no time component. Time is 12:00 AM
                 DateTime day = new DateTime(_currentMonth.Year, count + 1, 1);
                 childButton.DataContext = day;
@@ -746,7 +746,7 @@ namespace Avalonia.Controls.Primitives
             foreach (object child in YearView.Children)
             {
                 CalendarButton childButton = child as CalendarButton;
-                Debug.Assert(childButton != null, "childButton should not be null!");
+                Contract.Requires<ArgumentNullException>(childButton != null);
                 year = decade + count;
 
                 if (year <= DateTime.MaxValue.Year && year >= DateTime.MinValue.Year)
@@ -826,7 +826,7 @@ namespace Avalonia.Controls.Primitives
                 {
                     Owner.Focus();
                 }
-                Button b = sender as Button;
+                Button b = (Button)sender;
                 DateTime d;
 
                 if (b.IsEnabled)
@@ -863,7 +863,7 @@ namespace Avalonia.Controls.Primitives
                     Owner.Focus();
                 }
 
-                Button b = sender as Button;
+                Button b = (Button)sender;
                 if (b.IsEnabled)
                 {
                     Owner.OnPreviousClick();
@@ -878,7 +878,7 @@ namespace Avalonia.Controls.Primitives
                 {
                     Owner.Focus();
                 }
-                Button b = sender as Button;
+                Button b = (Button)sender;
 
                 if (b.IsEnabled)
                 {
@@ -891,8 +891,7 @@ namespace Avalonia.Controls.Primitives
         {
             if (Owner != null)
             {
-                CalendarDayButton b = sender as CalendarDayButton;
-                if (_isMouseLeftButtonDown && b != null && b.IsEnabled && !b.IsBlackout)
+                if (_isMouseLeftButtonDown && sender is CalendarDayButton b && b.IsEnabled && !b.IsBlackout)
                 {
                     // Update the states of all buttons to be selected starting
                     // from HoverStart to b
@@ -918,7 +917,7 @@ namespace Avalonia.Controls.Primitives
                                 Debug.Assert(b.DataContext != null, "The DataContext should not be null!");
                                 Owner.UnHighlightDays();
                                 Owner.HoverEndIndex = b.Index;
-                                Owner.HoverEnd = (DateTime)b.DataContext;
+                                Owner.HoverEnd = (DateTime?)b.DataContext;
                                 // Update the States of the buttons
                                 Owner.HighlightDays();
                                 return;
@@ -931,7 +930,7 @@ namespace Avalonia.Controls.Primitives
         {
             if (_isMouseLeftButtonDown)
             {
-                CalendarDayButton b = sender as CalendarDayButton;
+                CalendarDayButton b = (CalendarDayButton)sender;
                 // The button is in Pressed state. Change the state to normal.
                 if (e.Device.Captured == b)
                     e.Device.Capture(null);
@@ -973,7 +972,7 @@ namespace Avalonia.Controls.Primitives
                     if (b.IsEnabled && !b.IsBlackout)
                     {
                         DateTime selectedDate = (DateTime)b.DataContext;
-                        Debug.Assert(selectedDate != null, "selectedDate should not be null!");
+                        Contract.Requires<ArgumentNullException>(selectedDate != null);
                         _isMouseLeftButtonDown = true;
                         // null check is added for unit tests
                         if (e != null)
@@ -1149,7 +1148,7 @@ namespace Avalonia.Controls.Primitives
                 if (_isControlPressed && Owner.SelectionMode == CalendarSelectionMode.MultipleRange)
                 {
                     CalendarDayButton b = sender as CalendarDayButton;
-                    Debug.Assert(b != null, "The sender should be a non-null CalendarDayButton!");
+                    Contract.Requires<ArgumentNullException>(b != null);
 
                     if (b.IsSelected)
                     {
@@ -1169,7 +1168,7 @@ namespace Avalonia.Controls.Primitives
         private void Month_CalendarButtonMouseDown(object sender, PointerPressedEventArgs e)
         {
             CalendarButton b = sender as CalendarButton;
-            Debug.Assert(b != null, "The sender should be a non-null CalendarDayButton!");
+            Contract.Requires<ArgumentNullException>(b != null);
 
             _isMouseLeftButtonDownYearView = true;
 
@@ -1208,7 +1207,7 @@ namespace Avalonia.Controls.Primitives
             if (_isMouseLeftButtonDownYearView)
             {
                 CalendarButton b = sender as CalendarButton;
-                Debug.Assert(b != null, "The sender should be a non-null CalendarDayButton!");
+                Contract.Requires<ArgumentNullException>(b != null);
                 UpdateYearViewSelection(b);
             }
         }
@@ -1217,7 +1216,7 @@ namespace Avalonia.Controls.Primitives
         {
             if (_isMouseLeftButtonDownYearView)
             {
-                CalendarButton b = sender as CalendarButton;
+                CalendarButton b = (CalendarButton)sender;
                 // The button is in Pressed state. Change the state to normal.
                 if (e.Device.Captured == b)
                     e.Device.Capture(null);
diff --git a/src/Avalonia.Controls/Calendar/DatePicker.cs b/src/Avalonia.Controls/Calendar/DatePicker.cs
index 418ef50b2c..08608ad359 100644
--- a/src/Avalonia.Controls/Calendar/DatePicker.cs
+++ b/src/Avalonia.Controls/Calendar/DatePicker.cs
@@ -842,7 +842,7 @@ namespace Avalonia.Controls
         private void Calendar_KeyDown(object sender, KeyEventArgs e)
         {
             Calendar c = sender as Calendar;
-            Debug.Assert(c != null, "The Calendar should not be null!");
+            Contract.Requires<ArgumentNullException>(c != null);
 
             if (!e.Handled && (e.Key == Key.Enter || e.Key == Key.Space || e.Key == Key.Escape) && c.DisplayMode == CalendarMode.Month)
             {
diff --git a/src/Avalonia.Controls/Design.cs b/src/Avalonia.Controls/Design.cs
index ce52891749..894240a09f 100644
--- a/src/Avalonia.Controls/Design.cs
+++ b/src/Avalonia.Controls/Design.cs
@@ -1,5 +1,6 @@
 
 using System.Runtime.CompilerServices;
+using Avalonia.Styling;
 
 namespace Avalonia.Controls
 {
@@ -45,23 +46,18 @@ namespace Avalonia.Controls
         {
             return control.GetValue(DataContextProperty);
         }
-
-        static readonly ConditionalWeakTable<object, Control> Substitutes = new ConditionalWeakTable<object, Control>();
-
+        
         public static readonly AttachedProperty<Control> PreviewWithProperty = AvaloniaProperty
-            .RegisterAttached<AvaloniaObject, Control>("PreviewWith", typeof (Design));
+            .RegisterAttached<Style, Control>("PreviewWith", typeof (Design));
 
-        public static void SetPreviewWith(object target, Control control)
+        public static void SetPreviewWith(Style target, Control control)
         {
-            Substitutes.Remove(target);
-            Substitutes.Add(target, control);
+            target.SetValue(PreviewWithProperty, control);
         }
 
-        public static Control GetPreviewWith(object target)
+        public static Control GetPreviewWith(Style target)
         {
-            Control rv;
-            Substitutes.TryGetValue(target, out rv);
-            return rv;
+            return target.GetValue(PreviewWithProperty);
         }
 
         public static void ApplyDesignModeProperties(Control target, Control source)
diff --git a/src/Avalonia.Controls/DropDownItem.cs b/src/Avalonia.Controls/DropDownItem.cs
index 3fd80c4562..fb465e93ec 100644
--- a/src/Avalonia.Controls/DropDownItem.cs
+++ b/src/Avalonia.Controls/DropDownItem.cs
@@ -22,14 +22,13 @@ namespace Avalonia.Controls
         static DropDownItem()
         {
             FocusableProperty.OverrideDefaultValue<DropDownItem>(true);
-            IsFocusedProperty.Changed.Subscribe(x =>
-            {
-                var sender = x.Sender as IControl;
+        }
 
-                if (sender != null)
-                {
-                    ((IPseudoClasses)sender.Classes).Set(":selected", (bool)x.NewValue);
-                }
+        public DropDownItem()
+        {
+            this.GetObservable(DropDownItem.IsFocusedProperty).Subscribe(focused =>
+            {
+                PseudoClasses.Set(":selected", focused);                
             });
         }
 
diff --git a/src/Avalonia.Controls/Embedding/Offscreen/OffscreenTopLevel.cs b/src/Avalonia.Controls/Embedding/Offscreen/OffscreenTopLevel.cs
index cd2da692ba..4db16c71a5 100644
--- a/src/Avalonia.Controls/Embedding/Offscreen/OffscreenTopLevel.cs
+++ b/src/Avalonia.Controls/Embedding/Offscreen/OffscreenTopLevel.cs
@@ -57,7 +57,7 @@ namespace Avalonia.Controls.Embedding.Offscreen
         Type IStyleable.StyleKey => typeof(EmbeddableControlRoot);
         public void Dispose()
         {
-            PlatformImpl.Dispose();
+            PlatformImpl?.Dispose();
         }
     }
 }
diff --git a/src/Avalonia.Controls/Platform/InProcessDragSource.cs b/src/Avalonia.Controls/Platform/InProcessDragSource.cs
index e136efe2a9..52e09aba45 100644
--- a/src/Avalonia.Controls/Platform/InProcessDragSource.cs
+++ b/src/Avalonia.Controls/Platform/InProcessDragSource.cs
@@ -62,7 +62,7 @@ namespace Avalonia.Platform
 
             RawDragEvent rawEvent = new RawDragEvent(_dragDrop, type, root, pt, _draggedData, _allowedEffects);
             var tl = root.GetSelfAndVisualAncestors().OfType<TopLevel>().FirstOrDefault();
-            tl.PlatformImpl.Input(rawEvent);
+            tl.PlatformImpl?.Input(rawEvent);
 
             var effect = GetPreferredEffect(rawEvent.Effects & _allowedEffects, modifiers);
             UpdateCursor(root, effect);
diff --git a/src/Avalonia.Controls/Presenters/CarouselPresenter.cs b/src/Avalonia.Controls/Presenters/CarouselPresenter.cs
index c6ef5a14e9..e438843078 100644
--- a/src/Avalonia.Controls/Presenters/CarouselPresenter.cs
+++ b/src/Avalonia.Controls/Presenters/CarouselPresenter.cs
@@ -106,7 +106,6 @@ namespace Avalonia.Controls.Presenters
         /// <inheritdoc/>
         protected override void ItemsChanged(NotifyCollectionChangedEventArgs e)
         {
-            // TODO: Handle items changing.           
             switch (e.Action)
             {
                 case NotifyCollectionChangedAction.Remove:
@@ -115,9 +114,35 @@ namespace Avalonia.Controls.Presenters
                         var generator = ItemContainerGenerator;
                         var containers = generator.RemoveRange(e.OldStartingIndex, e.OldItems.Count);
                         Panel.Children.RemoveAll(containers.Select(x => x.ContainerControl));
+
+                        MoveToPage(-1, SelectedIndex);
                     }
                     break;
 
+                case NotifyCollectionChangedAction.Reset:
+                    {
+                        var generator = ItemContainerGenerator;
+                        var containers = generator.Containers.ToList();
+                        generator.Clear();
+                        Panel.Children.RemoveAll(containers.Select(x => x.ContainerControl));
+
+                        var newIndex = SelectedIndex;
+
+                        if(SelectedIndex < 0)
+                        {
+                            if(Items != null && Items.Count() > 0)
+                            {
+                                newIndex = 0;
+                            }
+                            else
+                            {
+                                newIndex = -1;
+                            }
+                        }
+                        
+                        MoveToPage(-1, newIndex);
+                    }
+                    break;     
             }
         }
 
diff --git a/src/Avalonia.Controls/TextBox.cs b/src/Avalonia.Controls/TextBox.cs
index 874d2a3229..2ea9319194 100644
--- a/src/Avalonia.Controls/TextBox.cs
+++ b/src/Avalonia.Controls/TextBox.cs
@@ -68,6 +68,10 @@ namespace Avalonia.Controls
         public static readonly StyledProperty<bool> UseFloatingWatermarkProperty =
             AvaloniaProperty.Register<TextBox, bool>(nameof(UseFloatingWatermark));
 
+        public static readonly DirectProperty<TextBox, string> NewLineProperty =
+            AvaloniaProperty.RegisterDirect<TextBox, string>(nameof(NewLine),
+                textbox => textbox.NewLine, (textbox, newline) => textbox.NewLine = newline);
+
         struct UndoRedoState : IEquatable<UndoRedoState>
         {
             public string Text { get; }
@@ -90,6 +94,7 @@ namespace Avalonia.Controls
         private UndoRedoHelper<UndoRedoState> _undoRedoHelper;
         private bool _isUndoingRedoing;
         private bool _ignoreTextChanges;
+        private string _newLine = Environment.NewLine;
         private static readonly string[] invalidCharacters = new String[1] { "\u007f" };
 
         static TextBox()
@@ -241,6 +246,15 @@ namespace Avalonia.Controls
             set { SetValue(TextWrappingProperty, value); }
         }
 
+        /// <summary>
+        /// Gets or sets which characters are inserted when Enter is pressed. Default: <see cref="Environment.NewLine"/>
+        /// </summary>
+        public string NewLine
+        {
+            get { return _newLine; }
+            set { SetAndRaise(NewLineProperty, ref _newLine, value); }
+        }
+
         protected override void OnTemplateApplied(TemplateAppliedEventArgs e)
         {
             _presenter = e.NameScope.Get<TextPresenter>("PART_TextPresenter");
@@ -498,7 +512,7 @@ namespace Avalonia.Controls
                 case Key.Enter:
                     if (AcceptsReturn)
                     {
-                        HandleTextInput("\r\n");
+                        HandleTextInput(NewLine);
                         handled = true;
                     }
 
diff --git a/src/Avalonia.Controls/Window.cs b/src/Avalonia.Controls/Window.cs
index c4a09ac043..3cbfdbd657 100644
--- a/src/Avalonia.Controls/Window.cs
+++ b/src/Avalonia.Controls/Window.cs
@@ -145,11 +145,9 @@ namespace Avalonia.Controls
             : base(impl)
         {
             impl.Closing = HandleClosing;
+            impl.WindowStateChanged = HandleWindowStateChanged;
             _maxPlatformClientSize = PlatformImpl?.MaxClientSize ?? default(Size);
             Screens = new Screens(PlatformImpl?.Screen);
-
-            if (PlatformImpl != null)
-                PlatformImpl.WindowStateChanged = s => WindowState = s;
         }
         
         /// <inheritdoc/>
@@ -318,6 +316,20 @@ namespace Avalonia.Controls
             return args.Cancel;
         }
 
+        protected virtual void HandleWindowStateChanged(WindowState state)
+        {
+            WindowState = state;
+
+            if (state == WindowState.Minimized)
+            {
+                Renderer.Stop();
+            }
+            else
+            {
+                Renderer.Start();
+            }
+        }
+
         /// <summary>
         /// Hides the window but does not close it.
         /// </summary>
diff --git a/src/Avalonia.DesignerSupport/DesignWindowLoader.cs b/src/Avalonia.DesignerSupport/DesignWindowLoader.cs
index d1958ac9bf..6dca479d38 100644
--- a/src/Avalonia.DesignerSupport/DesignWindowLoader.cs
+++ b/src/Avalonia.DesignerSupport/DesignWindowLoader.cs
@@ -36,8 +36,7 @@ namespace Avalonia.DesignerSupport
                 var styles = loaded as Styles;
                 if (styles != null)
                 {
-                    var substitute = Design.GetPreviewWith(styles) ??
-                                     styles.Select(Design.GetPreviewWith).FirstOrDefault(s => s != null);
+                    var substitute = styles.OfType<Style>().Select(Design.GetPreviewWith).FirstOrDefault(s => s != null);
                     if (substitute != null)
                     {
                         substitute.Styles.AddRange(styles);
diff --git a/src/Avalonia.Styling/Styling/Style.cs b/src/Avalonia.Styling/Styling/Style.cs
index 88ff695ba2..203f679683 100644
--- a/src/Avalonia.Styling/Styling/Style.cs
+++ b/src/Avalonia.Styling/Styling/Style.cs
@@ -15,7 +15,7 @@ namespace Avalonia.Styling
     /// <summary>
     /// Defines a style.
     /// </summary>
-    public class Style : IStyle, ISetStyleParent
+    public class Style : AvaloniaObject, IStyle, ISetStyleParent
     {
         private static Dictionary<IStyleable, List<IDisposable>> _applied =
             new Dictionary<IStyleable, List<IDisposable>>();
diff --git a/src/Avalonia.Themes.Default/Calendar.xaml b/src/Avalonia.Themes.Default/Calendar.xaml
index 5e4306c217..61b1224424 100644
--- a/src/Avalonia.Themes.Default/Calendar.xaml
+++ b/src/Avalonia.Themes.Default/Calendar.xaml
@@ -15,9 +15,10 @@
     <Setter Property="Template">
       <ControlTemplate>
         <StackPanel Name="Root"
-                    HorizontalAlignment="Center">
+                    HorizontalAlignment="Center"
+                    ClipToBounds="True">
 
-          <CalendarItem Name="CalendarItem"
+                    <CalendarItem Name="CalendarItem"
                         Background="{TemplateBinding Background}"
                         BorderBrush="{TemplateBinding BorderBrush}"
                         BorderThickness="{TemplateBinding BorderThickness}"
diff --git a/src/Avalonia.Visuals/Media/FontFamily.cs b/src/Avalonia.Visuals/Media/FontFamily.cs
index a4b4f5085a..70a4aee4cd 100644
--- a/src/Avalonia.Visuals/Media/FontFamily.cs
+++ b/src/Avalonia.Visuals/Media/FontFamily.cs
@@ -77,10 +77,10 @@ namespace Avalonia.Media
         /// <summary>
         /// Implicit conversion of string to FontFamily
         /// </summary>
-        /// <param name="fontFamily"></param>
-        public static implicit operator FontFamily(string fontFamily)
+        /// <param name="s"></param>
+        public static implicit operator FontFamily(string s)
         {
-            return new FontFamily(fontFamily);
+            return Parse(s);
         }
 
         /// <summary>
diff --git a/src/Markup/Avalonia.Markup/Data/MultiBinding.cs b/src/Markup/Avalonia.Markup/Data/MultiBinding.cs
index f6f62dcd1d..a3fa6880ac 100644
--- a/src/Markup/Avalonia.Markup/Data/MultiBinding.cs
+++ b/src/Markup/Avalonia.Markup/Data/MultiBinding.cs
@@ -10,6 +10,7 @@ using System.Reactive.Subjects;
 using Avalonia.Controls;
 using Avalonia.Data.Converters;
 using Avalonia.Metadata;
+using JetBrains.Annotations;
 
 namespace Avalonia.Data
 {
@@ -65,7 +66,7 @@ namespace Avalonia.Data
             var children = Bindings.Select(x => x.Initiate(target, null));
             var input = children.Select(x => x.Subject).CombineLatest().Select(x => ConvertValue(x, targetType));
             var mode = Mode == BindingMode.Default ?
-                targetProperty.GetMetadata(target.GetType()).DefaultBindingMode : Mode;
+                targetProperty?.GetMetadata(target.GetType()).DefaultBindingMode : Mode;
 
             switch (mode)
             {
diff --git a/src/Windows/Avalonia.Win32/SystemDialogImpl.cs b/src/Windows/Avalonia.Win32/SystemDialogImpl.cs
index e08fecbbd9..9b6bf57e92 100644
--- a/src/Windows/Avalonia.Win32/SystemDialogImpl.cs
+++ b/src/Windows/Avalonia.Win32/SystemDialogImpl.cs
@@ -54,7 +54,7 @@ namespace Avalonia.Win32
                 var fileBuffer = new char[256];
                 dialog.InitialFileName?.CopyTo(0, fileBuffer, 0, dialog.InitialFileName.Length);
 
-                string userSelectedExt = null;
+                string userSelectedExt = string.Empty;
 
 
                 var title = ToChars(dialog.Title);
diff --git a/tests/Avalonia.Controls.UnitTests/CarouselTests.cs b/tests/Avalonia.Controls.UnitTests/CarouselTests.cs
index 4d38ec9856..f36e5864f6 100644
--- a/tests/Avalonia.Controls.UnitTests/CarouselTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/CarouselTests.cs
@@ -1,11 +1,13 @@
 // Copyright (c) The Avalonia Project. All rights reserved.
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
+using System.Collections.ObjectModel;
 using System.Linq;
 using Avalonia.Controls.Presenters;
 using Avalonia.Controls.Primitives;
 using Avalonia.Controls.Templates;
 using Avalonia.LogicalTree;
+using Avalonia.VisualTree;
 using Xunit;
 
 namespace Avalonia.Controls.UnitTests
@@ -50,7 +52,7 @@ namespace Avalonia.Controls.UnitTests
             Assert.Single(target.GetLogicalChildren());
 
             var child = target.GetLogicalChildren().Single();
-            
+
             Assert.IsType<TextBlock>(child);
             Assert.Equal("Foo", ((TextBlock)child).Text);
         }
@@ -93,6 +95,208 @@ namespace Avalonia.Controls.UnitTests
             Assert.Equal(2, target.ItemContainerGenerator.Containers.Count());
         }
 
+        [Fact]
+        public void Selected_Item_Changes_To_First_Item_When_Items_Property_Changes()
+        {
+            var items = new ObservableCollection<string>
+            {
+               "Foo",
+               "Bar",
+               "FooBar"
+            };
+
+            var target = new Carousel
+            {
+                Template = new FuncControlTemplate<Carousel>(CreateTemplate),
+                Items = items,
+                IsVirtualized = false
+            };
+
+            target.ApplyTemplate();
+            target.Presenter.ApplyTemplate();
+
+            Assert.Single(target.GetLogicalChildren());
+
+            var child = target.GetLogicalChildren().Single();
+
+            Assert.IsType<TextBlock>(child);
+            Assert.Equal("Foo", ((TextBlock)child).Text);
+
+            var newItems = items.ToList();
+            newItems.RemoveAt(0);
+
+            target.Items = newItems;
+
+            child = target.GetLogicalChildren().Single();
+
+            Assert.IsType<TextBlock>(child);
+            Assert.Equal("Bar", ((TextBlock)child).Text);
+        }
+
+        [Fact]
+        public void Selected_Item_Changes_To_First_Item_When_Items_Property_Changes_And_Virtualized()
+        {
+            var items = new ObservableCollection<string>
+            {
+               "Foo",
+               "Bar",
+               "FooBar"
+            };
+
+            var target = new Carousel
+            {
+                Template = new FuncControlTemplate<Carousel>(CreateTemplate),
+                Items = items
+            };
+
+            target.ApplyTemplate();
+            target.Presenter.ApplyTemplate();
+
+            Assert.Single(target.GetLogicalChildren());
+
+            var child = target.GetLogicalChildren().Single();
+
+            Assert.IsType<TextBlock>(child);
+            Assert.Equal("Foo", ((TextBlock)child).Text);
+
+            var newItems = items.ToList();
+            newItems.RemoveAt(0);
+
+            target.Items = newItems;
+
+            child = target.GetLogicalChildren().Single();
+
+            Assert.IsType<TextBlock>(child);
+            Assert.Equal("Bar", ((TextBlock)child).Text);
+        }
+
+        [Fact]
+        public void Selected_Index_Changes_To_When_Items_Assigned_Null()
+        {
+            var items = new ObservableCollection<string>
+            {
+               "Foo",
+               "Bar",
+               "FooBar"
+            };
+
+            var target = new Carousel
+            {
+                Template = new FuncControlTemplate<Carousel>(CreateTemplate),
+                Items = items,
+                IsVirtualized = false
+            };
+
+            target.ApplyTemplate();
+            target.Presenter.ApplyTemplate();
+
+            Assert.Single(target.GetLogicalChildren());
+
+            var child = target.GetLogicalChildren().Single();
+
+            Assert.IsType<TextBlock>(child);
+            Assert.Equal("Foo", ((TextBlock)child).Text);
+
+            target.Items = null;
+
+            var numChildren = target.GetLogicalChildren().Count();
+
+            Assert.Equal(0, numChildren);
+            Assert.Equal(-1, target.SelectedIndex);
+        }
+
+        [Fact]
+        public void Selected_Index_Is_Maintained_Carousel_Created_With_Non_Zero_SelectedIndex()
+        {
+            var items = new ObservableCollection<string>
+            {
+               "Foo",
+               "Bar",
+               "FooBar"
+            };
+
+            var target = new Carousel
+            {
+                Template = new FuncControlTemplate<Carousel>(CreateTemplate),
+                Items = items,
+                IsVirtualized = false,
+                SelectedIndex = 2
+            };
+
+            target.ApplyTemplate();
+            target.Presenter.ApplyTemplate();
+
+            Assert.Equal("FooBar", target.SelectedItem);
+
+            var child = target.GetVisualDescendants().LastOrDefault();
+
+            Assert.IsType<TextBlock>(child);
+            Assert.Equal("FooBar", ((TextBlock)child).Text);
+        }
+
+        [Fact]
+        public void Selected_Item_Changes_To_Next_First_Item_When_Item_Removed_From_Beggining_Of_List()
+        {
+            var items = new ObservableCollection<string>
+            {
+               "Foo",
+               "Bar",
+               "FooBar"
+            };
+
+            var target = new Carousel
+            {
+                Template = new FuncControlTemplate<Carousel>(CreateTemplate),
+                Items = items,
+                IsVirtualized = false
+            };
+
+            target.ApplyTemplate();
+            target.Presenter.ApplyTemplate();
+
+            Assert.Single(target.GetLogicalChildren());
+
+            var child = target.GetLogicalChildren().Single();
+
+            Assert.IsType<TextBlock>(child);
+            Assert.Equal("Foo", ((TextBlock)child).Text);
+
+            items.RemoveAt(0);
+
+            child = target.GetLogicalChildren().Single();
+
+            Assert.IsType<TextBlock>(child);
+            Assert.Equal("Bar", ((TextBlock)child).Text);
+        }
+
+        [Fact]
+        public void Selected_Item_Changes_To_NextAvailable_Item_If_SelectedItem_Is_Removed_From_Middle()
+        {
+            var items = new ObservableCollection<string>
+            {
+               "Foo",
+               "Bar",
+               "FooBar"
+            };
+
+            var target = new Carousel
+            {
+                Template = new FuncControlTemplate<Carousel>(CreateTemplate),
+                Items = items,
+                IsVirtualized = false
+            };
+
+            target.ApplyTemplate();
+            target.Presenter.ApplyTemplate();
+
+            target.SelectedIndex = 1;
+
+            items.RemoveAt(1);
+
+            Assert.Equal(1, target.SelectedIndex);
+            Assert.Equal("FooBar", target.SelectedItem);
+        }
+
         private Control CreateTemplate(Carousel control)
         {
             return new CarouselPresenter
diff --git a/tests/Avalonia.Controls.UnitTests/TextBoxTests.cs b/tests/Avalonia.Controls.UnitTests/TextBoxTests.cs
index af461f07a4..4a8c171ecf 100644
--- a/tests/Avalonia.Controls.UnitTests/TextBoxTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/TextBoxTests.cs
@@ -247,6 +247,59 @@ namespace Avalonia.Controls.UnitTests
             }
         }
 
+        [Fact]
+        public void Press_Enter_Does_Not_Accept_Return()
+        {
+            using (UnitTestApplication.Start(Services))
+            {
+                var target = new TextBox
+                {
+                    Template = CreateTemplate(),
+                    AcceptsReturn = false,
+                    Text = "1234"
+                };
+
+                RaiseKeyEvent(target, Key.Enter, 0);
+
+                Assert.Equal("1234", target.Text);
+            }
+        }
+
+        [Fact]
+        public void Press_Enter_Add_Default_Newline()
+        {
+            using (UnitTestApplication.Start(Services))
+            {
+                var target = new TextBox
+                {
+                    Template = CreateTemplate(),
+                    AcceptsReturn = true
+                };
+
+                RaiseKeyEvent(target, Key.Enter, 0);
+
+                Assert.Equal(Environment.NewLine, target.Text);
+            }
+        }
+
+        [Fact]
+        public void Press_Enter_Add_Custom_Newline()
+        {
+            using (UnitTestApplication.Start(Services))
+            {
+                var target = new TextBox
+                {
+                    Template = CreateTemplate(),
+                    AcceptsReturn = true,
+                    NewLine = "Test"
+                };
+
+                RaiseKeyEvent(target, Key.Enter, 0);
+
+                Assert.Equal("Test", target.Text);
+            }
+        }
+
         [Theory]
         [InlineData(new object[] { false, TextWrapping.NoWrap, ScrollBarVisibility.Hidden })]
         [InlineData(new object[] { false, TextWrapping.Wrap, ScrollBarVisibility.Hidden })]