support for .NET framework 3.5

Still have bugs

Net35/HandyControl_Net35/Controls/Internal/InternalCanvas.cs

@@ -0,0 +1,64 @@
+using System.Windows;
+using System.Windows.Controls;
+
+namespace HandyControl.Controls
+{
+    internal class InternalCanvas : Canvas
+    {
+        internal static readonly DependencyProperty OrientationProperty = DependencyProperty.Register(
+            "Orientation", typeof(Orientation), typeof(InternalCanvas), new PropertyMetadata(default(Orientation)));
+
+        internal Orientation Orientation
+        {
+            get => (Orientation) GetValue(OrientationProperty);
+            set => SetValue(OrientationProperty, value);
+        }
+
+        protected override Size ArrangeOverride(Size arrangeSize)
+        {
+            foreach (UIElement internalChild in InternalChildren)
+            {
+                if (internalChild == null) continue;
+
+                var x = 0.0;
+                var y = 0.0;
+
+                if (Orientation == Orientation.Horizontal)
+                {
+                    x = (arrangeSize.Width - internalChild.DesiredSize.Width) / 2;
+
+                    var top = GetTop(internalChild);
+                    if (!double.IsNaN(top))
+                    {
+                        y = top;
+                    }
+                    else
+                    {
+                        var bottom = GetBottom(internalChild);
+                        if (!double.IsNaN(bottom))
+                            y = arrangeSize.Height - internalChild.DesiredSize.Height - bottom;
+                    }
+                }
+                else
+                {
+                    y = (arrangeSize.Height - internalChild.DesiredSize.Height) / 2;
+
+                    var left = GetLeft(internalChild);
+                    if (!double.IsNaN(left))
+                    {
+                        x = left;
+                    }
+                    else
+                    {
+                        var right = GetRight(internalChild);
+                        if (!double.IsNaN(right))
+                            x = arrangeSize.Width - internalChild.DesiredSize.Width - right;
+                    }
+                }
+
+                internalChild.Arrange(new Rect(new Point(x, y), internalChild.DesiredSize));
+            }
+            return arrangeSize;
+        }
+    }
+}