While in background:
Jan 12 11:20:14 iPhone-von-reBuy RebuyAppiOS[950] <Warning>: Warning: Unhandled exception: System.AggregateException: A Task's exception(s) were not observed either by Waiting on the Task or accessing its Exception property. As a result, the unobserved exception was rethrown by the finalizer thread. ---> System.NullReferenceException: Object reference not set to an instance of an object
at RebuyApp.iOS.Renderers.ExtendedMapsRenderer.OnElementChanged (Xamarin.Forms.Platform.iOS.ElementChangedEventArgs`1 e) <0x1000a97b0 + 0x00240> in <filename unknown>:0
at Xamarin.Forms.Platform.iOS.VisualElementRenderer`1[TElement].SetElement (Xamarin.Forms.Platform.iOS.TElement element) <0x100dc3ac0 + 0x0028f> in <filename unknown>:0
at Xamarin.Forms.Platform.iOS.VisualElementRenderer`1[TElement].Dispose (Boolean disposing) <0x100dc4288 + 0x000d3> in <filename unknown>:0
at Xamarin.Forms.Platform.iOS.ViewRenderer`2[TView,TNativeView].Dispose (Boolean disposing) <0x100dc2b00 + 0x0001f> in <filename unknown>:0
at Xamarin.Forms.Maps.iOS.MapRenderer.Dispose (Boolean disposing) <0x101428b54 + 0x00187> in <filename unknown>:0
at Foundation.NSObject.Dispose () <0x10071ad8c + 0x0001f> in <filename unknown>:0
at Xamarin.Forms.Platform.iOS.Platform.DisposeModelAndChildrenRenderers (Xamarin.Forms.Element view) <0x100dbf984 + 0x00117> in <filename unknown>:0
at Xamarin.Forms.Platform.iOS.Platform.HandleChildRemoved (System.Object sender, Xamarin.Forms.ElementEventArgs e) <0x100dbfd84 + 0x00013> in <filename unknown>:0
at Xamarin.Forms.Element.OnDescendantRemoved (Xamarin.Forms.Element child) <0x100ce85b4 + 0x0005f> in <filename unknown>:0
at Xamarin.Forms.Element.OnDescendantRemoved (Xamarin.Forms.Element child) <0x100ce85b4 + 0x00077> in <filename unknown>:0
at Xamarin.Forms.Element.OnChildRemoved (Xamarin.Forms.Element child) <0x100ce8448 + 0x00083> in <filename unknown>:0
at Xamarin.Forms.VisualElement.OnChildRemoved (Xamarin.Forms.Element child) <0x100cf1f50 + 0x00013> in <filename unknown>:0
at Xamarin.Forms.Page.OnInternalRemoved (Xamarin.Forms.VisualElement view) <0x100cacbd8 + 0x0006b> in <filename unknown>:0
at Xamarin.Forms.Page.InternalChildrenOnCollectionChanged (System.Object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e) <0x100cac990 + 0x0009b> in <filename unknown>:0
at System.Collections.ObjectModel.ObservableCollection`1[T].OnCollectionChanged (System.Collections.Specialized.NotifyCollectionChangedEventArgs e) <0x100173190 + 0x00063> in <filename unknown>:0
at System.Collections.ObjectModel.ObservableCollection`1[T].OnCollectionChanged (NotifyCollectionChangedAction action, System.Object item, Int32 index) <0x100173370 + 0x00067> in <filename unknown>:0
at System.Collections.ObjectModel.ObservableCollection`1[T].RemoveItem (Int32 index) <0x100172d74 + 0x00077> in <filename unknown>:0
at System.Collections.ObjectModel.Collection`1[T].Remove (System.Collections.ObjectModel.T item) <0x1002ce08c + 0x00087> in <filename unknown>:0
at Xamarin.Forms.NavigationPage+<PopAsyncInner>d__69.MoveNext () <0x100cab33c + 0x00207> in <filename unknown>:0
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) <0x100330354 + 0x000d4> in <filename unknown>:0
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) <0x10033027c + 0x000c7> in <filename unknown>:0
at System.Runtime.CompilerServices.TaskAwaiter`1[TResult].GetResult () <0x100330594 + 0x0003b> in <filename unknown>:0
at Xamarin.Forms.Platform.iOS.NavigationRenderer+<>c__DisplayClass49_0+<<RemoveViewControllers>b__0>d.MoveNext () <0x100dec7a8 + 0x000ab> in <filename unknown>:0
--- End of inner exception stack trace ---
---> (Inner Exception #0) System.NullReferenceException: Object reference not set to an instance of an object
at RebuyApp.iOS.Renderers.ExtendedMapsRenderer.OnElementChanged (Xamarin.Forms.Platform.iOS.ElementChangedEventArgs`1 e) <0x1000a97b0 + 0x00240> in <filename unknown>:0
at Xamarin.Forms.Platform.iOS.VisualElementRenderer`1[TElement].SetElement (Xamarin.Forms.Platform.iOS.TElement element) <0x100dc3ac0 + 0x0028f> in <filename unknown>:0
at Xamarin.Forms.Platform.iOS.VisualElementRenderer`1[TElement].Dispose (Boolean disposing) <0x100dc4288 + 0x000d3> in <filename unknown>:0
at Xamarin.Forms.Platform.iOS.ViewRenderer`2[TView,TNativeView].Dispose (Boolean disposing) <0x100dc2b00 + 0x0001f> in <filename unknown>:0
at Xamarin.Forms.Maps.iOS.MapRenderer.Dispose (Boolean disposing) <0x101428b54 + 0x00187> in <filename unknown>:0
at Foundation.NSObject.Dispose () <0x10071ad8c + 0x0001f> in <filename unknown>:0
at Xamarin.Forms.Platform.iOS.Platform.DisposeModelAndChildrenRenderers (Xamarin.Forms.Element view) <0x100dbf984 + 0x00117> in <filename unknown>:0
at Xamarin.Forms.Platform.iOS.Platform.HandleChildRemoved (System.Object sender, Xamarin.Forms.ElementEventArgs e) <0x100dbfd84 + 0x00013> in <filename unknown>:0
at Xamarin.Forms.Element.OnDescendantRemoved (Xamarin.Forms.Element child) <0x100ce85b4 + 0x0005f> in <filename unknown>:0
at Xamarin.Forms.Element.OnDescendantRemoved (Xamarin.Forms.Element child) <0x100ce85b4 + 0x00077> in <filename unknown>:0
at Xamarin.Forms.Element.OnChildRemoved (Xamarin.Forms.Element child) <0x100ce8448 + 0x00083> in <filename unknown>:0
at Xamarin.Forms.VisualElement.OnChildRemoved (Xamarin.Forms.Element child) <0x100cf1f50 + 0x00013> in <filename unknown>:0
at Xamarin.Forms.Page.OnInternalRemoved (Xamarin.Forms.VisualElement view) <0x100cacbd8 + 0x0006b> in <filename unknown>:0
at Xamarin.Forms.Page.InternalChildrenOnCollectionChanged (System.Object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e) <0x100cac990 + 0x0009b> in <filename unknown>:0
at System.Collections.ObjectModel.ObservableCollection`1[T].OnCollectionChanged (System.Collections.Specialized.NotifyCollectionChangedEventArgs e) <0x100173190 + 0x00063> in <filename unknown>:0
at System.Collections.ObjectModel.ObservableCollection`1[T].OnCollectionChanged (NotifyCollectionChangedAction action, System.Object item, Int32 index) <0x100173370 + 0x00067> in <filename unknown>:0
at System.Collections.ObjectModel.ObservableCollection`1[T].RemoveItem (Int32 index) <0x100172d74 + 0x00077> in <filename unknown>:0
at System.Collections.ObjectModel.Collection`1[T].Remove (System.Collections.ObjectModel.T item) <0x1002ce08c + 0x00087> in <filename unknown>:0
at Xamarin.Forms.NavigationPage+<PopAsyncInner>d__69.MoveNext () <0x100cab33c + 0x00207> in <filename unknown>:0
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) <0x100330354 + 0x000d4> in <filename unknown>:0
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) <0x10033027c + 0x000c7> in <filename unknown>:0
at System.Runtime.CompilerServices.TaskAwaiter`1[TResult].GetResult () <0x100330594 + 0x0003b> in <filename unknown>:0
at Xamarin.Forms.Platform.iOS.NavigationRenderer+<>c__DisplayClass49_0+<<RemoveViewControllers>b__0>d.MoveNext () <0x100dec7a8 + 0x000ab> in <filename unknown>:0 <---
When resuming from background:
2016/1/12 上午11:20:54 RebuyAppiOS[950]: Warning: Unhandled exception: System.NullReferenceException: Object reference not set to an instance of an object
at RebuyApp.iOS.Renderers.ExtendedMapsRenderer.regionChanged (System.Object sender, MapKit.MKMapViewChangeEventArgs e) <0x1000a9c6c + 0x0006c> in <filename unknown>:0
at (wrapper delegate-invoke) System.EventHandler`1[MapKit.MKMapViewChangeEventArgs]:invoke_void_object_TEventArgs (object,MapKit.MKMapViewChangeEventArgs)
at MapKit.MKMapView+_MKMapViewDelegate.RegionChanged (MapKit.MKMapView mapView, Boolean animated) <0x100726424 + 0x0004b> in <filename unknown>:0
at (wrapper managed-to-native) UIKit.UIApplication:UIApplicationMain (int,string[],intptr,intptr)
at UIKit.UIApplication.Main (System.String[] args, System.String principalClassName, System.String delegateClassName) <0x100700e8c + 0x0009b> in <filename unknown>:0
at RebuyApp.iOS.Application.Main (System.String[] args) <0x1000a63a4 + 0x0001b> in <filename unknown>:0