Implement the platform ticker

Ooui.Forms/Forms.cs

@@ -62,11 +62,6 @@ namespace Xamarin.Forms
                 Task.Run (action);
             }
 
-            public Ticker CreateTicker ()
-            {
-                throw new NotImplementedException ();
-            }
-
             public Assembly[] GetAssemblies ()
             {
                 return AppDomain.CurrentDomain.GetAssemblies ();
@@ -119,6 +114,31 @@ namespace Xamarin.Forms
                     }
                 }), null, (int)interval.TotalMilliseconds, (int)interval.TotalMilliseconds);
             }
+
+            public Ticker CreateTicker ()
+            {
+                return new OouiTicker ();
+            }
+
+            class OouiTicker : Ticker
+            {
+                Timer timer;
+                protected override void DisableTimer ()
+                {
+                    var t = timer;
+                    timer = null;
+                    t?.Dispose ();
+                }
+                protected override void EnableTimer ()
+                {
+                    if (timer != null)
+                        return;
+                    var interval = TimeSpan.FromSeconds (1.0 / Ooui.UI.Session.MaxFps);
+                    timer = new Timer ((_ => {
+                        this.SendSignals ();
+                    }), null, (int)interval.TotalMilliseconds, (int)interval.TotalMilliseconds);
+                }
+            }
         }
 
         public class ViewInitializedEventArgs

Ooui.Forms/Renderers/LabelRenderer.cs

@@ -74,6 +74,9 @@ namespace Ooui.Forms.Renderers
         {
             base.OnElementPropertyChanged (sender, e);
 
+            if (Control == null)
+                return;
+
             if (e.PropertyName == Xamarin.Forms.Label.HorizontalTextAlignmentProperty.PropertyName)
                 UpdateAlignment ();
             else if (e.PropertyName == Xamarin.Forms.Label.VerticalTextAlignmentProperty.PropertyName)

Ooui/UI.cs

@@ -522,9 +522,11 @@ namespace Ooui
             readonly HashSet<string> createdIds;
             readonly List<Message> queuedMessages = new List<Message> ();
 
+            public const int MaxFps = 30;
+
             readonly System.Timers.Timer sendThrottle;
             DateTime lastTransmitTime = DateTime.MinValue;
-            readonly TimeSpan throttleInterval = TimeSpan.FromSeconds (1.0 / 30); // 30 FPS max
+            readonly TimeSpan throttleInterval = TimeSpan.FromSeconds (1.0 / MaxFps);
             readonly double initialWidth;
             readonly double initialHeight;