iOS and Android timers should be runnable from any thread and execute… (#374)

* iOS and Android timers should be runnable from any thread and executed on the main thread

* removing unused Timer class declarations with minor refactoring efforts

* iOS and Android timers should be runnable from any thread and executed on the main thread

* removing bak file

* switch to v7

* add test code

9 files changed, 136 insertions, 224 deletions

diff --git a/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Bugzilla28953.cs b/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Bugzilla28953.cs
new file mode 100644
index 00000000..3a357863
--- /dev/null
+++ b/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Bugzilla28953.cs
@@ -0,0 +1,116 @@
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+using System;
+using System.Threading.Tasks;
+
+#if UITEST
+using Xamarin.UITest;
+using NUnit.Framework;
+#endif
+
+namespace Xamarin.Forms.Controls.Issues
+{
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.Bugzilla, 28953, "Device.StartTimer (still) behaves differently on different platforms", PlatformAffected.All)]
+	public class Bugzilla28953 : TestContentPage // or TestMasterDetailPage, etc ...
+	{
+		int count = 0, count2 = 0;
+		Label label2, label3;
+		bool shouldStop, shouldStop2;
+
+		protected override void Init()
+		{
+			var stackLayout = new StackLayout
+			{
+				Orientation = StackOrientation.Vertical,
+				VerticalOptions = LayoutOptions.Center,
+				Spacing = 20
+			};
+
+			var label1 = new Label
+			{
+				Text = "Click Start to start counting with a timer. Click Stop to reset. Both timers update text in UI thread."
+			};
+			stackLayout.Children.Add(label1);
+
+			label2 = new Label
+			{
+				Text = count.ToString(),
+				HorizontalTextAlignment = TextAlignment.Center,
+			};
+			stackLayout.Children.Add(label2);
+
+			label3 = new Label
+			{
+				Text = count2.ToString(),
+				HorizontalTextAlignment = TextAlignment.Center,
+			};
+			stackLayout.Children.Add(label3);
+
+			var button = new Button
+			{
+				Text = "Start"
+			};
+			button.Clicked += Button_Clicked;
+			stackLayout.Children.Add(button);
+
+			var button2 = new Button
+			{
+				Text = "Start (in background thread)"
+			};
+			button2.Clicked += Button_Clicked2;
+			stackLayout.Children.Add(button2);
+
+			Content = stackLayout;
+		}
+
+		private void Button_Clicked(object sender, EventArgs e)
+		{
+			var button = sender as Button;
+			if (button.Text == "Start")
+			{
+				(sender as Button).Text = "Stop";
+				shouldStop = false;
+
+				Device.StartTimer(TimeSpan.FromMilliseconds(100), () =>
+				{
+					label2.Text = count.ToString();
+					count++;
+					return !shouldStop;
+				});
+			}
+			else
+			{
+				button.Text = "Start";
+				shouldStop = true;
+				count = 0;
+			}
+		}
+
+		private void Button_Clicked2(object sender, EventArgs e)
+		{
+			var button = sender as Button;
+			if (button.Text == "Start (in background thread)")
+			{
+				(sender as Button).Text = "Stop (in background thread)";
+				shouldStop2 = false;
+
+				Task.Run(() =>
+				{
+					Device.StartTimer(TimeSpan.FromMilliseconds(100), () =>
+					{
+						label3.Text = count2.ToString();
+						count2++;
+						return !shouldStop2;
+					});
+				});
+			}
+			else
+			{
+				button.Text = "Start (in background thread)";
+				shouldStop2 = true;
+				count2 = 0;
+			}
+		}
+	}
+}
\ No newline at end of file
diff --git a/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Xamarin.Forms.Controls.Issues.Shared.projitems b/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Xamarin.Forms.Controls.Issues.Shared.projitems
index 36ed04cb..16a2199d 100644
--- a/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Xamarin.Forms.Controls.Issues.Shared.projitems
+++ b/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Xamarin.Forms.Controls.Issues.Shared.projitems
@@ -36,6 +36,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla28570.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla28796.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla28939.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Bugzilla28953.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla29107.xaml.cs">
       <DependentUpon>Bugzilla29107.xaml</DependentUpon>
     </Compile>
diff --git a/Xamarin.Forms.Core.UnitTests/MockPlatformServices.cs b/Xamarin.Forms.Core.UnitTests/MockPlatformServices.cs
index 5109cbb4..e8519b9e 100644
--- a/Xamarin.Forms.Core.UnitTests/MockPlatformServices.cs
+++ b/Xamarin.Forms.Core.UnitTests/MockPlatformServices.cs
@@ -119,57 +119,6 @@ namespace Xamarin.Forms.Core.UnitTests
 			return AppDomain.CurrentDomain.GetAssemblies ();
 		}
 
-		public ITimer CreateTimer (Action<object> callback)
-		{
-			return new MockTimer (new Timer (o => callback(o)));
-		}
-
-		public ITimer CreateTimer (Action<object> callback, object state, int dueTime, int period)
-		{
-			return new MockTimer (new Timer (o => callback(o), state, dueTime, period));
-		}
-
-		public ITimer CreateTimer (Action<object> callback, object state, long dueTime, long period)
-		{
-			return new MockTimer (new Timer (o => callback(o), state, dueTime, period));
-		}
-
-		public ITimer CreateTimer (Action<object> callback, object state, TimeSpan dueTime, TimeSpan period)
-		{
-			return new MockTimer (new Timer (o => callback(o), state, dueTime, period));
-		}
-
-		public ITimer CreateTimer (Action<object> callback, object state, uint dueTime, uint period)
-		{
-			return new MockTimer (new Timer (o => callback(o), state, dueTime, period));
-		}
-
-		public class MockTimer : ITimer
-		{
-			readonly Timer timer;
-			public MockTimer (Timer timer)
-			{
-				this.timer = timer;
-			}
-
-			public void Change (int dueTime, int period)
-			{
-				timer.Change (dueTime, period);
-			}
-			public void Change (long dueTime, long period)
-			{
-				timer.Change (dueTime, period);
-			}
-			public void Change (TimeSpan dueTime, TimeSpan period)
-			{
-				timer.Change (dueTime, period);
-			}
-			public void Change (uint dueTime, uint period)
-			{
-				timer.Change (dueTime, period);
-			}
-		}
-
 		public IIsolatedStorageFile GetUserStoreForApplication ()
 		{
 #if WINDOWS_PHONE
diff --git a/Xamarin.Forms.Core/ITimer.cs b/Xamarin.Forms.Core/ITimer.cs
deleted file mode 100644
index ba867dba..00000000
--- a/Xamarin.Forms.Core/ITimer.cs
+++ /dev/null
@@ -1,13 +0,0 @@
-using System;
-
-namespace Xamarin.Forms
-{
-	//this will go once Timer is included in Pcl profiles
-	internal interface ITimer
-	{
-		void Change(int dueTime, int period);
-		void Change(long dueTime, long period);
-		void Change(TimeSpan dueTime, TimeSpan period);
-		void Change(uint dueTime, uint period);
-	}
-}
\ No newline at end of file
diff --git a/Xamarin.Forms.Core/Xamarin.Forms.Core.csproj b/Xamarin.Forms.Core/Xamarin.Forms.Core.csproj
index 9bfb7ba2..2e10a1b2 100644
--- a/Xamarin.Forms.Core/Xamarin.Forms.Core.csproj
+++ b/Xamarin.Forms.Core/Xamarin.Forms.Core.csproj
@@ -369,7 +369,6 @@
     <Compile Include="Tweener.cs" />
     <Compile Include="IPlatformServices.cs" />
     <Compile Include="UriTypeConverter.cs" />
-    <Compile Include="ITimer.cs" />
     <Compile Include="IIsolatedStorageFile.cs" />
     <Compile Include="Grid.cs" />
     <Compile Include="GridCalc.cs" />
diff --git a/Xamarin.Forms.Platform.Android/Forms.cs b/Xamarin.Forms.Platform.Android/Forms.cs
index 3d2a735c..1ecf76d3 100644
--- a/Xamarin.Forms.Platform.Android/Forms.cs
+++ b/Xamarin.Forms.Platform.Android/Forms.cs
@@ -410,22 +410,15 @@ namespace Xamarin.Forms
 
 			public void StartTimer(TimeSpan interval, Func<bool> callback)
 			{
-				Timer timer = null;
-				bool invoking = false;
-				TimerCallback onTimeout = o =>
+				var handler = new Handler(Looper.MainLooper);
+				handler.PostDelayed(() =>
 				{
-					if (!invoking)
-					{
-						invoking = true;
-						BeginInvokeOnMainThread(() =>
-						{
-							if (!callback())
-								timer.Dispose();
-							invoking = false;
-						});
-					}
-				};
-				timer = new Timer(onTimeout, null, interval, interval);
+					if (callback())
+						StartTimer(interval, callback);
+
+					handler.Dispose();
+					handler = null;
+				}, (long)interval.TotalMilliseconds);
 			}
 
 			double ConvertTextAppearanceToSize(int themeDefault, int deviceDefault, double defaultValue)
@@ -472,36 +465,6 @@ namespace Xamarin.Forms
 				return false;
 			}
 
-			public class _Timer : ITimer
-			{
-				readonly Timer _timer;
-
-				public _Timer(Timer timer)
-				{
-					_timer = timer;
-				}
-
-				public void Change(int dueTime, int period)
-				{
-					_timer.Change(dueTime, period);
-				}
-
-				public void Change(long dueTime, long period)
-				{
-					_timer.Change(dueTime, period);
-				}
-
-				public void Change(TimeSpan dueTime, TimeSpan period)
-				{
-					_timer.Change(dueTime, period);
-				}
-
-				public void Change(uint dueTime, uint period)
-				{
-					_timer.Change(dueTime, period);
-				}
-			}
-
 			public class _IsolatedStorageFile : IIsolatedStorageFile
 			{
 				readonly IsolatedStorageFile _isolatedStorageFile;
diff --git a/Xamarin.Forms.Platform.WP8/WP8PlatformServices.cs b/Xamarin.Forms.Platform.WP8/WP8PlatformServices.cs
index 30623088..cd9f44f9 100644
--- a/Xamarin.Forms.Platform.WP8/WP8PlatformServices.cs
+++ b/Xamarin.Forms.Platform.WP8/WP8PlatformServices.cs
@@ -137,36 +137,6 @@ namespace Xamarin.Forms
 			return 'a' + v - 10;
 		}
 
-		public class _Timer : ITimer
-		{
-			readonly Timer _timer;
-
-			public _Timer(Timer timer)
-			{
-				_timer = timer;
-			}
-
-			public void Change(int dueTime, int period)
-			{
-				_timer.Change(dueTime, period);
-			}
-
-			public void Change(long dueTime, long period)
-			{
-				_timer.Change(dueTime, period);
-			}
-
-			public void Change(TimeSpan dueTime, TimeSpan period)
-			{
-				_timer.Change(dueTime, period);
-			}
-
-			public void Change(uint dueTime, uint period)
-			{
-				_timer.Change(dueTime, period);
-			}
-		}
-
 		public class _IsolatedStorageFile : IIsolatedStorageFile
 		{
 			readonly IsolatedStorageFile _isolatedStorageFile;
diff --git a/Xamarin.Forms.Platform.WinRT/WindowsBasePlatformServices.cs b/Xamarin.Forms.Platform.WinRT/WindowsBasePlatformServices.cs
index 49589a8a..310b66c3 100644
--- a/Xamarin.Forms.Platform.WinRT/WindowsBasePlatformServices.cs
+++ b/Xamarin.Forms.Platform.WinRT/WindowsBasePlatformServices.cs
@@ -29,12 +29,12 @@ namespace Xamarin.Forms.Platform.WinRT
 {
 	internal abstract class WindowsBasePlatformServices : IPlatformServices
 	{
-		CoreDispatcher _dispatcher;
+		readonly CoreDispatcher _dispatcher;
 
-		public WindowsBasePlatformServices(CoreDispatcher dispatcher)
+		protected WindowsBasePlatformServices(CoreDispatcher dispatcher)
 		{
 			if (dispatcher == null)
-				throw new ArgumentNullException("dispatcher");
+				throw new ArgumentNullException(nameof(dispatcher));
 
 			_dispatcher = dispatcher;
 		}
@@ -57,9 +57,8 @@ namespace Xamarin.Forms.Platform.WinRT
 			IReadOnlyList<StorageFile> files = query.GetFilesAsync().AsTask().Result;
 
 			var assemblies = new List<Assembly>(files.Count);
-			for (var i = 0; i < files.Count; i++)
+			foreach (StorageFile file in files)
 			{
-				StorageFile file = files[i];
 				try
 				{
 					Assembly assembly = Assembly.Load(new AssemblyName { Name = Path.GetFileNameWithoutExtension(file.Name) });
@@ -133,35 +132,5 @@ namespace Xamarin.Forms.Platform.WinRT
 					timer.Stop();
 			};
 		}
-
-		internal class WindowsTimer : ITimer
-		{
-			readonly Timer _timer;
-
-			public WindowsTimer(Timer timer)
-			{
-				_timer = timer;
-			}
-
-			public void Change(int dueTime, int period)
-			{
-				_timer.Change(dueTime, period);
-			}
-
-			public void Change(long dueTime, long period)
-			{
-				Change(TimeSpan.FromMilliseconds(dueTime), TimeSpan.FromMilliseconds(period));
-			}
-
-			public void Change(TimeSpan dueTime, TimeSpan period)
-			{
-				_timer.Change(dueTime, period);
-			}
-
-			public void Change(uint dueTime, uint period)
-			{
-				Change(TimeSpan.FromMilliseconds(dueTime), TimeSpan.FromMilliseconds(period));
-			}
-		}
 	}
 }
\ No newline at end of file
diff --git a/Xamarin.Forms.Platform.iOS/Forms.cs b/Xamarin.Forms.Platform.iOS/Forms.cs
index 06cb1312..5361e13f 100644
--- a/Xamarin.Forms.Platform.iOS/Forms.cs
+++ b/Xamarin.Forms.Platform.iOS/Forms.cs
@@ -68,9 +68,7 @@ namespace Xamarin.Forms
 
 		internal static void SendViewInitialized(this VisualElement self, UIView nativeView)
 		{
-			var viewInitialized = ViewInitialized;
-			if (viewInitialized != null)
-				viewInitialized(self, new ViewInitializedEventArgs { View = self, NativeView = nativeView });
+			ViewInitialized?.Invoke(self, new ViewInitializedEventArgs { View = self, NativeView = nativeView });
 		}
 
 		class iOSExpressionSearch : ExpressionVisitor, IExpressionSearch
@@ -117,15 +115,9 @@ namespace Xamarin.Forms
 
 			public override Size PixelScreenSize { get; }
 
-			public override Size ScaledScreenSize
-			{
-				get { return _scaledScreenSize; }
-			}
+			public override Size ScaledScreenSize => _scaledScreenSize;
 
-			public override double ScalingFactor
-			{
-				get { return _scalingFactor; }
-			}
+			public override double ScalingFactor => _scalingFactor;
 
 			protected override void Dispose(bool disposing)
 			{
@@ -136,7 +128,7 @@ namespace Xamarin.Forms
 
 		class IOSPlatformServices : IPlatformServices
 		{
-			static readonly MD5CryptoServiceProvider Checksum = new MD5CryptoServiceProvider();
+			static readonly MD5CryptoServiceProvider s_checksum = new MD5CryptoServiceProvider();
 
 			public void BeginInvokeOnMainThread(Action action)
 			{
@@ -155,7 +147,7 @@ namespace Xamarin.Forms
 
 			public string GetMD5Hash(string input)
 			{
-				var bytes = Checksum.ComputeHash(Encoding.UTF8.GetBytes(input));
+				var bytes = s_checksum.ComputeHash(Encoding.UTF8.GetBytes(input));
 				var ret = new char[32];
 				for (var i = 0; i < 16; i++)
 				{
@@ -198,10 +190,7 @@ namespace Xamarin.Forms
 				return new _IsolatedStorageFile(IsolatedStorageFile.GetUserStoreForApplication());
 			}
 
-			public bool IsInvokeRequired
-			{
-				get { return !NSThread.IsMain; }
-			}
+			public bool IsInvokeRequired => !NSThread.IsMain;
 
 			public void OpenUriAction(Uri uri)
 			{
@@ -210,8 +199,7 @@ namespace Xamarin.Forms
 
 			public void StartTimer(TimeSpan interval, Func<bool> callback)
 			{
-				NSTimer timer = null;
-				timer = NSTimer.CreateRepeatingScheduledTimer(interval, t =>
+				NSTimer timer = NSTimer.CreateRepeatingTimer(interval, t =>
 				{
 					if (!callback())
 						t.Invalidate();
@@ -238,36 +226,6 @@ namespace Xamarin.Forms
 				return 'a' + v - 10;
 			}
 
-			public class _Timer : ITimer
-			{
-				readonly Timer _timer;
-
-				public _Timer(Timer timer)
-				{
-					_timer = timer;
-				}
-
-				public void Change(int dueTime, int period)
-				{
-					_timer.Change(dueTime, period);
-				}
-
-				public void Change(long dueTime, long period)
-				{
-					_timer.Change(dueTime, period);
-				}
-
-				public void Change(TimeSpan dueTime, TimeSpan period)
-				{
-					_timer.Change(dueTime, period);
-				}
-
-				public void Change(uint dueTime, uint period)
-				{
-					_timer.Change(dueTime, period);
-				}
-			}
-
 			public class _IsolatedStorageFile : IIsolatedStorageFile
 			{
 				readonly IsolatedStorageFile _isolatedStorageFile;