add tool tip support for annotations

Source/Examples/ExampleLibrary/Annotations/EllipseAnnotationExamples.cs

@@ -19,11 +19,53 @@ public static PlotModel EllipseAnnotation()
             var model = new PlotModel { Title = "EllipseAnnotation" };
             model.Axes.Add(new LinearAxis { Position = AxisPosition.Bottom });
             model.Axes.Add(new LinearAxis { Position = AxisPosition.Left });
-            model.Annotations.Add(new EllipseAnnotation { X = 20, Y = 60, Width = 20, Height = 15, Text = "EllipseAnnotation", TextRotation = 10, Fill = OxyColor.FromAColor(99, OxyColors.Green), Stroke = OxyColors.Black, StrokeThickness = 2 });
+            model.Annotations.Add(new EllipseAnnotation
+            {
+                X = 20,
+                Y = 60,
+                Width = 20,
+                Height = 15,
+                Text = "EllipseAnnotation",
+                ToolTip = "EllipseAnnotation",
+                TextRotation = 10,
+                Fill = OxyColor.FromAColor(99, OxyColors.Green),
+                Stroke = OxyColors.Black,
+                StrokeThickness = 2
+            });
 
-            model.Annotations.Add(new EllipseAnnotation { X = 20, Y = 20, Width = 20, Height = 20, Fill = OxyColor.FromAColor(99, OxyColors.Green), Stroke = OxyColors.Black, StrokeThickness = 2 });
-            model.Annotations.Add(new EllipseAnnotation { X = 30, Y = 20, Width = 20, Height = 20, Fill = OxyColor.FromAColor(99, OxyColors.Red), Stroke = OxyColors.Black, StrokeThickness = 2 });
-            model.Annotations.Add(new EllipseAnnotation { X = 25, Y = 30, Width = 20, Height = 20, Fill = OxyColor.FromAColor(99, OxyColors.Blue), Stroke = OxyColors.Black, StrokeThickness = 2 });
+            model.Annotations.Add(new EllipseAnnotation
+            {
+                X = 20,
+                Y = 20,
+                Width = 20,
+                Height = 20,
+                Fill = OxyColor.FromAColor(99, OxyColors.Green),
+                ToolTip = "Green",
+                Stroke = OxyColors.Black,
+                StrokeThickness = 2
+            });
+            model.Annotations.Add(new EllipseAnnotation
+            {
+                X = 30,
+                Y = 20,
+                Width = 20,
+                Height = 20,
+                Fill = OxyColor.FromAColor(99, OxyColors.Red),
+                ToolTip = "Red",
+                Stroke = OxyColors.Black,
+                StrokeThickness = 2
+            });
+            model.Annotations.Add(new EllipseAnnotation
+            {
+                X = 25,
+                Y = 30,
+                Width = 20,
+                Height = 20,
+                Fill = OxyColor.FromAColor(99, OxyColors.Blue),
+                ToolTip = "Blue",
+                Stroke = OxyColors.Black,
+                StrokeThickness = 2
+            });
             return model;
         }
     }

Source/Examples/ExampleLibrary/Example.cs

@@ -30,7 +30,7 @@ public Example(PlotModel model, IPlotController controller = null)
         /// <value>
         /// The controller.
         /// </value>
-        public IPlotController Controller { get; private set; }
+        public IPlotController Controller { get; set; }
 
         /// <summary>
         /// Gets the model.

Source/Examples/ExampleLibrary/ExampleInfo.cs

@@ -32,7 +32,7 @@ public class ExampleInfo
         /// <summary>
         /// The un-modified example.
         /// </summary>
-        private Example Example;
+        public Example Example { get; private set; }
 
         /// <summary>
         /// The examples for this example info.

Source/OxyPlot.Maui.Skia/Manipulators/TouchTrackerManipulator.cs

@@ -57,6 +57,11 @@ public TouchTrackerManipulator(IPlotView plotView)
         /// <remarks>This parameter is ignored if <see cref="PointsOnly"/> is equal to <c>False</c>.</remarks>
         public bool CheckDistanceBetweenPoints { get; set; }
 
+        /// <summary>
+        ///  Gets or sets a value indicating whether to track annotations.
+        /// </summary>
+        public bool IsTrackAnnotations { get; set; } = false;
+
         /// <summary>
         /// Occurs when a manipulation is complete.
         /// </summary>
@@ -151,6 +156,10 @@ private void UpdateTracker(ScreenPoint position)
                     this.PlotView.HideTracker();
                 }
 
+                if (IsTrackAnnotations)
+                {
+                    TrackAnnotations(position);
+                }
                 return;
             }
 
@@ -174,5 +183,35 @@ private void UpdateTracker(ScreenPoint position)
                 actualModel.RaiseTrackerChanged(result);
             }
         }
+
+        /// <summary>
+        /// Track Annotations
+        /// </summary>
+        /// <param name="sp"></param>
+        private void TrackAnnotations(ScreenPoint sp)
+        {
+            foreach (var annotation in PlotView.ActualModel.Annotations
+                         .Where(x => !string.IsNullOrEmpty(x.ToolTip))
+                         .Reverse())
+            {
+                var args = new HitTestArguments(sp, FiresDistance);
+                var res = annotation.HitTest(args);
+
+                if (res == null)
+                    continue;
+
+                var dp = annotation.InverseTransform(sp);
+                var result = new TrackerHitResult
+                {
+                    Position = sp,
+                    DataPoint = dp,
+                    Text = annotation.ToolTip,
+                    PlotModel = this.PlotView.ActualModel
+                };
+                this.PlotView.ShowTracker(result);
+                this.PlotView.ActualModel.RaiseTrackerChanged(result);
+                break;
+            }
+        }
     }
 }

Source/OxyplotMauiSample/Pages/ExampleBrowser.xaml.cs

@@ -1,6 +1,9 @@
 using ExampleLibrary;
 using System.Collections.ObjectModel;
 using System.Windows.Input;
+using OxyPlot;
+using OxyPlot.Maui.Skia;
+using OxyPlot.Maui.Skia.Core;
 
 namespace OxyplotMauiSample
 {
@@ -29,14 +32,46 @@ private async void ListView_OnItemSelected(object sender, SelectedItemChangedEve
                 return;
 
             var exampleInfo = e.SelectedItem as ExampleInfo;
+            if (exampleInfo == null)
+                return;
+
             var page = new PlotViewPage
             {
                 ExampleInfo = exampleInfo
             };
+
+            // try add tracker support for annotations
+            if (exampleInfo.Tags.Contains("Annotations") && exampleInfo.PlotController == null)
+            {
+                exampleInfo.Example.Controller = CreateAnnotationTrackController();
+            }
             await Navigation.PushAsync(page);
 
             LvExamples.SelectedItem = null;
         }
+
+        private IPlotController CreateAnnotationTrackController()
+        {
+            var controller = new OxyPlot.Maui.Skia.PlotController();
+            controller.UnbindTouchDown();
+
+            var snapTrackTouch = new DelegatePlotCommand<OxyTouchEventArgs>((view, c, args) =>
+                c.AddTouchManipulator(view, new OxyPlot.Maui.Skia.Manipulators.TouchTrackerManipulator(view)
+                {
+                    Snap = true,
+                    PointsOnly = true,
+                    LockToInitialSeries = false,
+                    IsTrackAnnotations = true
+                }, args));
+
+            var cmd = new CompositeDelegateViewCommand<OxyTouchEventArgs>(
+                snapTrackTouch,
+                OxyPlot.Maui.Skia.PlotCommands.PanZoomByTouch
+            );
+            controller.BindTouchDown(cmd);
+
+            return controller;
+        }
     }
 
     public class ExampleBrowserViewModel : ViewModelBase