Fabulous: NRE on real device

Created on 12 Jul 2019 · 62Comments · Source: fsprojects/Fabulous

Hello, i am developing an fabulous app and currently experiencing weird issue while running my app on real device (Xiaomi mi8 if that does matter anything).
I have a view, which has two "states": first is just a label with "no content" text
and second is a ListView. On first load i am getting the error below. On next view loads all works fine. I am guessing this could be tied to fact that i have two different kind of visual tree in each state and when Fabulous trying to calculate the diff for ObservableCollection, it simpy cannot find the previous one. But anyway, any help and clues of what is going on is greatly appreciated

Unable to update view:: System.NullReferenceException: Object reference not set to an instance of an object.
at Xamarin.Forms.Platform.Android.PageRenderer.Xamarin.Forms.Platform.Android.IOrderedTraversalController.UpdateTraversalOrder () [0x000a4] in D:\a\1\sXamarin.Forms.Platform.Android\Renderers\PageRenderer.cs:177
at Xamarin.Forms.Platform.Android.VisualElementRenderer1[TElement].UpdateParentPageTraversalOrder () [0x00025] in D:\a\1\s\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:404 at Xamarin.Forms.Platform.Android.VisualElementRenderer1[TElement].OnElementPropertyChanged (System.Object sender, System.ComponentModel.PropertyChangedEventArgs e) [0x00116] in D:\a\1\sXamarin.Forms.Platform.Android\VisualElementRenderer.cs:369
at (wrapper delegate-invoke) .invoke_void_object_PropertyChangedEventArgs(object,System.ComponentModel.PropertyChangedEventArgs)
at Xamarin.Forms.BindableObject.OnPropertyChanged (System.String propertyName) [0x00000] in D:\a\1\sXamarin.Forms.Core\
BindableObject.cs:211
at Xamarin.Forms.Element.OnPropertyChanged (System.String propertyName) [0x00000] in D:\a\1\sXamarin.Forms.Core\Element.cs:353
at Xamarin.Forms.Element.set_Parent (Xamarin.Forms.Element value) [0x00094] in D:\a\1\sXamarin.Forms.Core\Element.cs:210
at Xamarin.Forms.Element.OnChildRemoved (Xamarin.Forms.Element child) [0x00000] in D:\a\1\sXamarin.Forms.Core\Element.cs:335
at Xamarin.Forms.VisualElement.OnChildRemoved (Xamarin.Forms.Element child) [0x00000] in D:\a\1\sXamarin.Forms.Core\VisualElement.cs:750
at Xamarin.Forms.Layout1[T].OnChildRemoved (Xamarin.Forms.Element child) [0x00000] in D:\a\1\s\Xamarin.Forms.Core\Layout.cs:41 at Xamarin.Forms.Layout.OnInternalRemoved (Xamarin.Forms.View view) [0x00012] in D:\a\1\s\Xamarin.Forms.Core\Layout.cs:464 at Xamarin.Forms.Layout.InternalChildrenOnCollectionChanged (System.Object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e) [0x0002b] in D:\a\1\s\Xamarin.Forms.Core\Layout.cs:427 at (wrap per delegate-invoke) <Module>.invoke_void_object_NotifyCollectionChangedEventArgs(object,System.Collections.Specialized.NotifyCollectionChangedEventArgs) at System.Collections.ObjectModel.ObservableCollection1[T].OnCollectionChanged (System.Collections.Specialized.NotifyCollectionChangedEventArgs e) [0x00018] in /Users/builder/jenkins/workspace/xamarin-android-d16-1/xamarin-android/external/mono/external/corefx/src/System.ObjectModel/src/System/Collections/ObjectModel/ObservableCollection.cs:263
at System.Collections.ObjectModel.ObservableCollection1[T].OnCollectionChanged (System.Collections.Specialized.NotifyCollectionChangedAction action, System.Object oldItem, System.Object newItem, System.Int32 index) [0x00000] in /Users/builder/jenkins/workspace/xamarin-android-d16-1/xamarin-android/external/mono/external/corefx/src/System.ObjectModel/src/System/Collections/ObjectModel/ObservableCollection.cs:354 at System.Collections.ObjectModel.ObservableCollection1[T].SetItem (System.Int32 index, T item) [
0x0001c] in /Users/builder/jenkins/workspace/xamarin-android-d16-1/xamarin-android/external/mono/external/corefx/src/System.ObjectModel/src/System/Collections/ObjectModel/ObservableCollection.cs:210
at System.Collections.ObjectModel.Collection1[T].set_Item (System.Int32 index, T value) [0x0002b] in /Users/builder/jenkins/workspace/xamarin-android-d16-1/xamarin-android/external/mono/external/corefx/src/Common/src/CoreLib/System/Collections/ObjectModel/Collection.cs:61 at Xamarin.Forms.ObservableWrapper2[TTrack,TRestrict].set_Item (System.Int32 index, TRestrict value) [0x00029] in D:\a\1\sXamarin.Forms.Core\ObservableWrapper.cs:140
at Fabulous.DynamicViews.Converters.updateCollectionGeneric$cont@387[T,TargetT] (Microsoft.FSharp.Core.FSharpValueOption1[T] prevCollOpt, System.Collections.Generic.IList1[T] targetColl, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] create, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] attach, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] canReuse, Microsoft.FSharp.Core .FSharpFunc2[T,TResult] update, T[] coll, Microsoft.FSharp.Core.Unit unitVar) [0x000ec] in /Git/Github/Fabulous/src/Fabulous.Core/ViewConverters.fs:407
at Fabulous.DynamicViews.Converters.updateCollectionGeneric[T,TargetT] (Microsoft.FSharp.Core.FSharpValueOption1[T] prevCollOpt, Microsoft.FSharp.Core.FSharpValueOption1[T] collOpt, System.Collections.Generic.IList1[T] targetColl, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] create, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] attach, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] canReuse, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] update) [0x00060] in /Git/Github/Fabulous/src/Fabulous.Core/ViewConverters.fs:383 at Fabulous.DynamicViews.ViewBuilders.UpdateGrid (Microsoft.FSharp.Core.FSharpValueOption1[T] prevOpt, Fabulous.DynamicViews.ViewElement curr, Xamarin.Forms.Grid target) [0x00465] in /Git/Github/Fabulous/src/Fabulous.Core/Xamarin.Forms.Core.fs:5320
at .$Xamarin.Forms.[email protected] (Mic
rosoft.FSharp.Core.FSharpValueOption1[T] prevOpt, Fabulous.DynamicViews.ViewElement curr, Xamarin.Forms.Grid target) [0x00000] in /Git/Github/Fabulous/src/Fabulous.Core/Xamarin.Forms.Core.fs:5258 at Fabulous.DynamicViews.Converters.updateCollectionGeneric$cont@387[T,TargetT] (Microsoft.FSharp.Core.FSharpValueOption1[T] prevCollOpt, System.Collections.Generic.IList1[T] targetColl, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] create, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] attach, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] canReuse, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] update, T[] coll, Microsoft.FSharp.Core.Unit unitVar) [0x0010e] in /Git/Github/Fabulous/src/Fabulous.Core/ViewConverters.fs:411 at Fabulous.DynamicViews.Converters.updateCollectionGeneric[T,TargetT] (Microsoft.FSharp.Core.FSharpValueOption1[T] prevCollOpt, Microsoft.FSharp.Core.FSharpValueOption1[T] collOpt, System.Collections.Generic.IList1[T] targetColl, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] create, Micros oft.FSharp.Core.FSharpFunc2[T,TResult] attach, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] canReuse, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] update) [0x00060] in /Git/Github/Fabulous/src/Fabulous.Core/ViewConverters.fs:383
at Fabulous.DynamicViews.ViewBuilders.UpdateGrid (Microsoft.FSharp.Core.FSharpValueOption1[T] prevOpt, Fabulous.DynamicViews.ViewElement curr, Xamarin.Forms.Grid target) [0x00465] in /Git/Github/Fabulous/src/Fabulous.Core/Xamarin.Forms.Core.fs:5320 at <StartupCode$Fabulous-Core>[email protected] (Microsoft.FSharp.Core.FSharpValueOption1[T] prevOpt, Fabulous.DynamicViews.ViewElement curr, Xamarin.Forms.Grid target) [0x00000] in /Git/Github/Fabulous/src/Fabulous.Core/Xamarin.Forms.Core.fs:5258
at Fabulous.DynamicViews.ViewBuilders.UpdateContentView (Microsoft.FSharp.Core.FSharpValueOption1[T] prevOpt, Fabulous.DynamicViews.ViewElement curr, Xamarin.Forms.ContentView target) [0x001c6] in /Git/Github/Fabulous/src/Fabulous.Core/Xamarin.Forms .Core.fs:6565 at <StartupCode$Fabulous-Core>[email protected] (Microsoft.FSharp.Core.FSharpValueOption1[T] prevOpt, Fabulous.DynamicViews.ViewElement curr, Xamarin.Forms.ContentView target) [0x00000] in /Git/Github/Fabulous/src/Fabulous.Core/Xamarin.Forms.Core.fs:6543
at Fabulous.DynamicViews.Converters.updateCollectionGeneric$cont@387[T,TargetT] (Microsoft.FSharp.Core.FSharpValueOption1[T] prevCollOpt, System.Collections.Generic.IList1[T] targetColl, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] create, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] attach, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] canReuse, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] update, T[] coll, Microsoft.FSharp.Core.Unit unitVar) [0x0010e] in /Git/Github/Fabulous/src/Fabulous.Core/ViewConverters.fs:411
at Fabulous.DynamicViews.Converters.updateCollectionGeneric[T,TargetT] (Microsoft.FSharp.Core.FSharpValueOption1[T] prevCollOpt, Microsoft.FSharp.Core.FSharpValueOption1[T] co
llOpt, System.Collections.Generic.IList1[T] targetColl, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] create, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] attach, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] canReuse, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] update) [0x00060] in /Git/Github/Fabulous/src/Fabulous.Core/ViewConverters.fs:383 at Fabulous.DynamicViews.ViewBuilders.UpdateGrid (Microsoft.FSharp.Core.FSharpValueOption1[T] prevOpt, Fabulous.DynamicViews.ViewElement curr, Xamarin.Forms.Grid target) [0x00465] in /Git/Github/Fabulous/src/Fabulous.Core/Xamarin.Forms.Core.fs:5320
at .$Xamarin.Forms.[email protected] (Microsoft.FSharp.Core.FSharpValueOption1[T] prevOpt, Fabulous.DynamicViews.ViewElement curr, Xamarin.Forms.Grid target) [0x00000] in /Git/Github/Fabulous/src/Fabulous.Core/Xamarin.Forms.Core.fs:5258 at Fabulous.DynamicViews.ViewBuilders.UpdateContentPage (Microsoft.FSharp.Core.FSharpValueOption1[T] prevOpt, Fabulous.DynamicViews.
ViewElement curr, Xamarin.Forms.ContentPage target) [0x00239] in /Git/Github/Fabulous/src/Fabulous.Core/Xamarin.Forms.Core.fs:12613
at .$Xamarin.Forms.[email protected] (Microsoft.FSharp.Core.FSharpValueOption1[T] prevOpt, Fabulous.DynamicViews.ViewElement curr, Xamarin.Forms.ContentPage target) [0x00000] in /Git/Github/Fabulous/src/Fabulous.Core/Xamarin.Forms.Core.fs:12585 at Fabulous.DynamicViews.Converters.updateNavigationPages (Microsoft.FSharp.Core.FSharpValueOption1[T] prevCollOpt, Microsoft.FSharp.Core.FSharpValueOption1[T] collOpt, Xamarin.Forms.NavigationPage target, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] attach) [0x00274] in /Git/Github/Fabulous/src/Fabulous.Core/ViewConverters.fs:694
at Fabulous.DynamicViews.ViewBuilders.UpdateNavigationPage (Microsoft.FSharp.Core.FSharpValueOption1[T] prevOpt, Fabulous.DynamicViews.ViewElement curr, Xamarin.Forms.NavigationPage target) [0x00339] in /Git/Github/Fabulous/src/Fabulous.Core/Xamar in.Forms.Core.fs:11975 at <StartupCode$Fabulous-Core>[email protected] (Microsoft.FSharp.Core.FSharpValueOption1[T] prevOpt, Fabulous.DynamicViews.ViewElement curr, Xamarin.Forms.NavigationPage target) [0x00000] in /Git/Github/Fabulous/src/Fabulous.Core/Xamarin.Forms.Core.fs:11927
at Fabulous.Core.ProgramRunner2[model,msg].updateView (model updatedModel) [0x00067] in /Git/Github/Fabulous/src/Fabulous.Core/ElmishProgram.fs:92 at Fabulous.Core.ProgramRunner2[model,msg].processMsg (msg msg) [0x0002e] in /Git/Github/Fabulous/src/Fabulous.Core/ElmishProgram.fs:68
07-12 16:56:22.842 I/mono-stdout(31427): Unable to update view:: System.NullReferenceException: Object reference not set to an instance of an object.
07-12 16:56:22.842 I/mono-stdout(31427): at Xamarin.Forms.Platform.Android.PageRenderer.Xamarin.Forms.Platform.Android.IOrderedTraversalController.UpdateTraversalOrder () [0x000a4] in D:\a\1\sXamarin.Forms.Platform.Android\Renderers\PageRenderer.cs:177
07-12 16:56:22.842 I/mono-stdout(31427): at Xamarin.Forms.Platform.Android.VisualElementRenderer1[TElement].UpdateParentPageTraversalOrder () [0x00025] in D:\a\1\s\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:404 07-12 16:56:22.842 I/mono-stdout(31427): at Xamarin.Forms.Platform.Android.VisualElementRenderer1[TElement].OnElementPropertyChanged (System.Object sender, System.ComponentModel.PropertyChangedEventArgs e) [0x00116] in D:\a\1\sXamarin.Forms.Platform.Android\VisualElementRenderer.cs:369
07-12 16:56:22.842 I/mono-stdout(31427): at (wrapper delegate-invoke) .invoke_void_object_PropertyChangedEventArgs(object,System.ComponentModel.PropertyChangedEventArgs)
07-12 16:56:22.842 I/mono-stdout(31427): at Xamarin.Forms.BindableObject.OnPropertyChanged (System.String propertyName) [0x00000] in D:\a\1\sXamarin.Forms.Core\BindableObject.cs:211
07-12 16:56:22.842 I/mono-stdout(31427): at Xamarin.Forms.Element.OnPropertyChanged (System.String propertyName) [0x00000] in D:\a\1\sXamarin.Forms.Core\Element.cs:353
07-12 16:56:22.842 I/mono-stdout(31427): at Xamarin.Forms.Element.set_Parent (Xamarin.Forms.Element value) [0x00094] in D:\a\1\sXamarin.Forms.Core\Element.cs:210
07-12 16:56:22.842 I/mono-stdout(31427): at Xamarin.Forms.Element.OnChildRemoved (Xamarin.Forms.Element child) [0x00000] in D:\a\1\sXamarin.Forms.Core\Element.cs:335
07-12 16:56:22.842 I/mono-stdout(31427): at Xamarin.Forms.VisualElement.OnChildRemoved (Xamarin.Forms.Element child) [0x00000] in D:\a\1\sXamarin.Forms.Core\VisualElement.cs:750
07-12 16:56:22.842 I/mono-stdout(31427): at Xamarin.Forms.Layout1[T].OnChildRemoved (Xamarin.Forms.Element child) [0x00000] in D:\a\1\s\Xamarin.Forms.Core\Layout.cs:41 07-12 16:56:22.842 I/mono-stdout(31427): at Xamarin.Forms.Layout.OnInternalRemoved (Xamarin.Forms.View view) [0x00012] in D:\a\1\s\Xamarin.Forms.Core\Layout.cs:464 07-12 16:56:22.842 I/mono-stdout(31427): at Xamarin.Forms.Layout.InternalChildrenOnCollectionChanged (System.Object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e) [0x0002b] in D:\a\1\s\Xamarin.Forms.Core\Layout.cs:427 07-12 16:56:22.842 I/mono-stdout(31427): at (wrapper delegate-invoke) <Module>.invoke_void_object_NotifyCollectionChangedEventArgs(object,System.Collections.Specialized.NotifyCollectionChangedEventArgs) 07-12 16:56:22.842 I/mono-stdout(31427): at System.Collections.ObjectModel.ObservableCollection1[T].OnCollectionChanged (System.Collections.Specialized.NotifyCollectionChangedEventArgs e) [0x00018] in /Users/builder/jenkins/workspace/xamarin-android-d16-1/xamarin-android/external/mono/external/corefx/src/System.ObjectModel/src/System/Collections/ObjectModel/ObservableCollection.cs:263
07-12 16:56:22.842 I/mono-stdout(31427): at System.Collections.ObjectModel.ObservableCollection1[T].OnCollectionChanged (System.Collections.Specialized.NotifyCollectionChangedAction action, System.Object oldItem, System.Object newItem, System.Int32 index) [0x00000] in /Users/builder/jenkins/workspace/xamarin-android-d16-1/xamarin-android/external/mono/external/corefx/src/System.ObjectModel/src/System/Collections/ObjectModel/ObservableCollection.cs:354 07-12 16:56:22.842 I/mono-stdout(31427): at System.Collections.ObjectModel.ObservableCollection1[T].SetItem (System.Int32 index, T item) [0x0001c] in /Users/builder/jenkins/workspace/xamarin-android-d16-1/xamarin-android/external/mono/external/corefx/src/System.ObjectModel/src/System/Collections/ObjectModel/ObservableCollection.cs:210
07-12 16:56:22.842 I/mono-stdout(31427): at System.Collections.ObjectModel.Collection1[T].set_Item (System.Int32 index, T value) [0x0002b] in /Users/builder/jenkins/workspace/xamarin-android-d16-1/xamarin-android/external/mono/external/corefx/src/Common/src/CoreLib/System/Collections/ObjectModel/Collection.cs:61 07-12 16:56:22.842 I/mono-stdout(31427): at Xamarin.Forms.ObservableWrapper2[TTrack,TRestrict].set_Item (System.Int32 index, TRestrict value) [0x00029] in D:\a\1\sXamarin.Forms.Core\ObservableWrapper.cs:140
07-12 16:56:22.843 I/mono-stdout(31427): at Fabulous.DynamicViews.Converters.updateCollectionGeneric$cont@387[T,TargetT] (Microsoft.FSharp.Core.FSharpValueOption1[T] prevCollOpt, System.Collections.Generic.IList1[T] targetColl, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] create, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] attach, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] canReuse, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] update, T[] coll, Microsoft.FSharp.Core.Unit unitVar) [0x000ec] in /Git/Github/Fabulous/src/Fabulous.Core/ViewConverters.fs:407
07-12 16:56:22.843 I/mono-stdout(31427): at Fabulous.DynamicViews.Converters.updateCollectionGeneric[T,TargetT] (Microsoft.FSharp.Core.FSharpValueOption1[T] prevCollOpt, Microsoft.FSharp.Core.FSharpValueOption1[T] collOpt, System.Collections.Generic.IList1[T] targetColl, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] create, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] attach, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] canReuse, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] update) [0x00060] in /Git/Github/Fabulous/src/Fabulous.Core/ViewConverters.fs:383 07-12 16:56:22.843 I/mono-stdout(31427): at Fabulous.DynamicViews.ViewBuilders.UpdateGrid (Microsoft.FSharp.Core.FSharpValueOption1[T] prevOpt, Fabulous.DynamicViews.ViewElement curr, Xamarin.Forms.Grid target) [0x00465] in /Git/Github/Fabulous/src/Fabulous.Core/Xamarin.Forms.Core.fs:5320
07-12 16:56:22.843 I/mono-stdout(31427): at .$Xamarin.Forms.[email protected] (Microsoft.FSharp.Core.FSharpValueOption1[T] prevOpt, Fabulous.DynamicViews.ViewElement curr, Xamarin.Forms.Grid target) [0x00000] in /Git/Github/Fabulous/src/Fabulous.Core/Xamarin.Forms.Core.fs:5258 07-12 16:56:22.843 I/mono-stdout(31427): at Fabulous.DynamicViews.Converters.updateCollectionGeneric$cont@387[T,TargetT] (Microsoft.FSharp.Core.FSharpValueOption1[T] prevCollOpt, System.Collections.Generic.IList1[T] targetColl, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] create, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] attach, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] canReuse, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] update, T[] coll, Microsoft.FSharp.Core.Unit unitVar) [0x0010e] in /Git/Github/Fabulous/src/Fabulous.Core/ViewConverters.fs:411 07-12 16:56:22.843 I/mono-stdout(31427): at Fabulous.DynamicViews.Converters.updateCollectionGeneric[T,TargetT] (Microsoft.FSharp.Core.FSharpValueOption1[T] prevCollOpt, Microsoft.FSharp.Core.FSharpValueOption1[T] collOpt, System.Collections.Generic.IList1[T] targetColl, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] create, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] attach, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] canReuse, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] update) [0x00060] in /Git/Github/Fabulous/src/Fabulous.Core/ViewConverters.fs:383
07-12 16:56:22.843 I/mono-stdout(31427): at Fabulous.DynamicViews.ViewBuilders.UpdateGrid (Microsoft.FSharp.Core.FSharpValueOption1[T] prevOpt, Fabulous.DynamicViews.ViewElement curr, Xamarin.Forms.Grid target) [0x00465] in /Git/Github/Fabulous/src/Fabulous.Core/Xamarin.Forms.Core.fs:5320 07-12 16:56:22.843 I/mono-stdout(31427): at <StartupCode$Fabulous-Core>[email protected] (Microsoft.FSharp.Core.FSharpValueOption1[T] prevOpt, Fabulous.DynamicViews.ViewElement curr, Xamarin.Forms.Grid target) [0x00000] in /Git/Github/Fabulous/src/Fabulous.Core/Xamarin.Forms.Core.fs:5258
07-12 16:56:22.843 I/mono-stdout(31427): at Fabulous.DynamicViews.ViewBuilders.UpdateContentView (Microsoft.FSharp.Core.FSharpValueOption1[T] prevOpt, Fabulous.DynamicViews.ViewElement curr, Xamarin.Forms.ContentView target) [0x001c6] in /Git/Github/Fabulous/src/Fabulous.Core/Xamarin.Forms.Core.fs:6565 07-12 16:56:22.843 I/mono-stdout(31427): at <StartupCode$Fabulous-Core>[email protected] (Microsoft.FSharp.Core.FSharpValueOption1[T] prevOpt, Fabulous.DynamicViews.ViewElement curr, Xamarin.Forms.ContentView target) [0x00000] in /Git/Github/Fabulous/src/Fabulous.Core/Xamarin.Forms.Core.fs:6543
07-12 16:56:22.843 I/mono-stdout(31427): at Fabulous.DynamicViews.Converters.updateCollectionGeneric$cont@387[T,TargetT] (Microsoft.FSharp.Core.FSharpValueOption1[T] prevCollOpt, System.Collections.Generic.IList1[T] targetColl, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] create, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] attach, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] canReuse, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] update, T[] coll, Microsoft.FSharp.Core.Unit unitVar) [0x0010e] in /Git/Github/Fabulous/src/Fabulous.Core/ViewConverters.fs:411
07-12 16:56:22.843 I/mono-stdout(31427): at Fabulous.DynamicViews.Converters.updateCollectionGeneric[T,TargetT] (Microsoft.FSharp.Core.FSharpValueOption1[T] prevCollOpt, Microsoft.FSharp.Core.FSharpValueOption1[T] collOpt, System.Collections.Generic.IList1[T] targetColl, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] create, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] attach, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] canReuse, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] update) [0x00060] in /Git/Github/Fabulous/src/Fabulous.Core/ViewConverters.fs:383 07-12 16:56:22.843 I/mono-stdout(31427): at Fabulous.DynamicViews.ViewBuilders.UpdateGrid (Microsoft.FSharp.Core.FSharpValueOption1[T] prevOpt, Fabulous.DynamicViews.ViewElement curr, Xamarin.Forms.Grid target) [0x00465] in /Git/Github/Fabulous/src/Fabulous.Core/Xamarin.Forms.Core.fs:5320
07-12 16:56:22.843 I/mono-stdout(31427): at .$Xamarin.Forms.[email protected] (Microsoft.FSharp.Core.FSharpValueOption1[T] prevOpt, Fabulous.DynamicViews.ViewElement curr, Xamarin.Forms.Grid target) [0x00000] in /Git/Github/Fabulous/src/Fabulous.Core/Xamarin.Forms.Core.fs:5258 07-12 16:56:22.843 I/mono-stdout(31427): at Fabulous.DynamicViews.ViewBuilders.UpdateContentPage (Microsoft.FSharp.Core.FSharpValueOption1[T] prevOpt, Fabulous.DynamicViews.ViewElement curr, Xamarin.Forms.ContentPage target) [0x00239] in /Git/Github/Fabulous/src/Fabulous.Core/Xamarin.Forms.Core.fs:12613
07-12 16:56:22.843 I/mono-stdout(31427): at .$Xamarin.Forms.[email protected] (Microsoft.FSharp.Core.FSharpValueOption1[T] prevOpt, Fabulous.DynamicViews.ViewElement curr, Xamarin.Forms.ContentPage target) [0x00000] in /Git/Github/Fabulous/src/Fabulous.Core/Xamarin.Forms.Core.fs:12585 07-12 16:56:22.843 I/mono-stdout(31427): at Fabulous.DynamicViews.Converters.updateNavigationPages (Microsoft.FSharp.Core.FSharpValueOption1[T] prevCollOpt, Microsoft.FSharp.Core.FSharpValueOption1[T] collOpt, Xamarin.Forms.NavigationPage target, Microsoft.FSharp.Core.FSharpFunc2[T,TResult] attach) [0x00274] in /Git/Github/Fabulous/src/Fabulous.Core/ViewConverters.fs:694
07-12 16:56:22.843 I/mono-stdout(31427): at Fabulous.DynamicViews.ViewBuilders.UpdateNavigationPage (Microsoft.FSharp.Core.FSharpValueOption1[T] prevOpt, Fabulous.DynamicViews.ViewElement curr, Xamarin.Forms.NavigationPage target) [0x00339] in /Git/Github/Fabulous/src/Fabulous.Core/Xamarin.Forms.Core.fs:11975 07-12 16:56:22.843 I/mono-stdout(31427): at <StartupCode$Fabulous-Core>[email protected] (Microsoft.FSharp.Core.FSharpValueOption1[T] prevOpt, Fabulous.DynamicViews.ViewElement curr, Xamarin.Forms.NavigationPage target) [0x00000] in /Git/Github/Fabulous/src/Fabulous.Core/Xamarin.Forms.Core.fs:11927
07-12 16:56:22.843 I/mono-stdout(31427): at Fabulous.Core.ProgramRunner2[model,msg].updateView (model updatedModel) [0x00067] in /Git/Github/Fabulous/src/Fabulous.Core/ElmishProgram.fs:92 07-12 16:56:22.843 I/mono-stdout(31427): at Fabulous.Core.ProgramRunner2[model,msg].processMsg (msg msg) [0x0002e] in /Git/Github/Fabulous/src/Fabulous.Core/ElmishProgram.fs:68

android needs repro

Source

vshapenko

Most helpful comment

@vshapenko
Your example created the error from #492 which @Happypig375 discovered on antoher device (Motorola G6) maybe your issue and the one from @Happypig375 are related.

Will try to identify what is happenend here that makes this stuff go crazy.

SergejDK on 19 Jul 2019

👍3

All 62 comments

@vshapenko Do you have a sample code showcasing this issue?

TimLariviere on 12 Jul 2019

Looks like, sounds like and smells like my encounter in #343.

Happypig375 on 12 Jul 2019

@vshapenko Do you have a sample code showcasing this issue?

Sample code was something like this:

if(model.Flag) then View.ContentView() else View.List.View()

I have omitted all the details here as unrelated to bug.

Problem does not reproduce on emulator, and it reproduces for every such view on every device only once.

I have fixed it by drawing ListView always regardless of flag. Looks like there is a bug in ObservableCollection content comparsion. At first, we do not have any listview, only content view. At second pass, we have a listview, but do not have previous. And at third pass we memoize the list view and comparsion works as designed.

vshapenko on 12 Jul 2019

I'm getting the same issue on a Samsung S8. The emulator works perfectly fine but a debug build on the device errors with the same error. We also have an if statement that shows two completely different trees

Using Fabulous.XamarinForms 0.41 and the latest patch release for Xamarin.Forms 4.1.0.581479

This is the code that explodes. The moment Type changes from Timed to something else I get the above error.

fsharp if model.Type = Timed then yield View.StackLayout ( children=[ // checkbox View.Label(text = "Time limit (mins)") ]) yield View.Entry(text = (if model.TimeLimited then string model.Duration else String.Empty), keyboard = Keyboard.Numeric) else yield View.Label(text = "Number of repetitions") yield View.Entry(text = string model.Repetitions)

marto83 on 16 Jul 2019

Please include an entire project if you don't have repro steps

Happypig375 on 17 Jul 2019

Unfortunately, @vshapenko & @marto83, I don't reproduce with the code snippets you gave.
It works fine in both the emulator and a real device (Xiaomi Redmi Note 7).

Could you write a small project where you have the issue, please?
Thanks

TimLariviere on 17 Jul 2019

I will spend some time this weekend trying to isolate it and create a small project.

What complicates matters is that it works fine on some android devices.

marto83 on 17 Jul 2019

👍2

You might want to check the device architecture. For example, #492 repros under armeabi-v7a but not x86.

Happypig375 on 17 Jul 2019

Unfortunately, @vshapenko & @marto83, I don't reproduce with the code snippets you gave.
It works fine in both the emulator and a real device (Xiaomi Redmi Note 7).

Could you write a small project where you have the issue, please?
Thanks

@TimLariviere for now, i can only give my thoughts on steps on repro:

Create a view function, which renders different views based on model condition.
First view rendered should be non - listview(i.e. label etc)
Send update to model which causes the listview to be rendered.
Also i have a dependsOn on items and listview render

vshapenko on 17 Jul 2019

Also a cause of a problem is https://github.com/fsprojects/Fabulous/blob/master/Fabulous.XamarinForms/src/Fabulous.XamarinForms.Core/ViewConverters.fs#L383 I think there should be additional Option.ofObj before matching

vshapenko on 17 Jul 2019

Also ViewConverters.fs:168. Looks like there is a problem with IList parameter,which can be null

vshapenko on 17 Jul 2019

I suggest to check all the params in such functions on null because of interop

vshapenko on 17 Jul 2019

After spending days isolating #492 and #522, I am currently stuck on this bug. I hope this can be fixed soon.

Happypig375 on 18 Jul 2019

This bug isn't tied to ListViews as I also hit this with AbsoluteLayout.

Happypig375 on 18 Jul 2019

I think this one is related too: https://github.com/xamarin/Xamarin.Forms/pull/6415

vshapenko on 18 Jul 2019

```fs// Copyright 2018-2019 Fabulous contributors. See LICENSE.md for license.
namespace ReproApp

open System.Diagnostics
open Fabulous
open Fabulous.XamarinForms
open Xamarin.Forms

module App =
type Model =
{ Flag:bool }

type Msg =
    |Flag


let initModel = {Flag=true }

let init () = initModel, Cmd.none



let update msg model =
    match msg with
    |Flag->{model with Flag=not model.Flag},Cmd.none

let view (model: Model) dispatch =
    View.ContentPage(
       content=View.Grid(
           rowdefs=["auto";"*"],
           children =
               [
                 yield View.Button (text="SetFlag", command= (fun ()->dispatch Flag))
                 if(model.Flag) then yield (View.Label(text="Flag set")).GridRow(1)
                 else yield View.ListView(items=([1..100]|>List.map (fun x->View.Label(text=string x)))).GridRow(1)


               ]
               )
       )

// Note, this declaration is needed if you enable LiveUpdate
let program = Program.mkProgram init update view

type App () as app =
inherit Application ()

let runner = 
    App.program

if DEBUG

    |> Program.withConsoleTrace

endif

    |> XamarinFormsProgram.run app

if DEBUG

// Uncomment this line to enable live update in debug mode. 
// See https://fsprojects.github.io/Fabulous/tools.html for further  instructions.
//
//do runner.EnableLiveUpdate()

endif

// Uncomment this code to save the application state to app.Properties using Newtonsoft.Json
// See https://fsprojects.github.io/Fabulous/models.html for further  instructions.

if APPSAVE

let modelId = "model"
override __.OnSleep() = 

    let json = Newtonsoft.Json.JsonConvert.SerializeObject(runner.CurrentModel)
    Console.WriteLine("OnSleep: saving model into app.Properties, json = {0}", json)

    app.Properties.[modelId] <- json

override __.OnResume() = 
    Console.WriteLine "OnResume: checking for model in app.Properties"
    try 
        match app.Properties.TryGetValue modelId with
        | true, (:? string as json) -> 

            Console.WriteLine("OnResume: restoring model from app.Properties, json = {0}", json)
            let model = Newtonsoft.Json.JsonConvert.DeserializeObject<App.Model>(json)

            Console.WriteLine("OnResume: restoring model from app.Properties, model = {0}", (sprintf "%0A" model))
            runner.SetCurrentModel (model, Cmd.none)

        | _ -> ()
    with ex -> 
        App.program.onError("Error while restoring model found in app.Properties", ex)

override this.OnStart() = 
    Console.WriteLine "OnStart: using same logic as OnResume()"
    this.OnResume()

endif

```

@TimLariviere here is small repro. On my Xialomi Mi 8 throws NRE on second button click

vshapenko on 18 Jul 2019

👍3

@vshapenko Use ```fs instead of ``` to get syntax highlighting

Edit: The code block still ends with ```, so only change the start!

Happypig375 on 18 Jul 2019

👍1

I can confirm that I get the same error on Samsung S8

marto83 on 18 Jul 2019

🎉1 👍1

Well, it's this time you desperately want it to crash, but it won't...

Tried it on macOS / Windows, emulator / real device (Xiaomi Redmi Note 7), asked a few people to test it with their own devices (LG G6 & Sony Xperia).
No crash.

I will try to write a UI test for it and use App Center to run the project for your devices (Samsung S8, Xiaomi Mi 8).
Hoping to produce something useful...

@SergejDK Could you also test it if you have an Android device, please?

TimLariviere on 18 Jul 2019

It crashes on button click.Crash is just a record in log and there is no redraw

vshapenko on 18 Jul 2019

I tried it on my device (Motorola G6) and it works without issues.
I'll try this on some different architecure...

@vshapenko @marto83
Maybe some information is needed from you, just in case I can build the same env as you have.
Mono version
Android version
VS/VS4Mac Version

SergejDK on 18 Jul 2019

Tried it with all available architecure and different emulator but still can not reproduce....

Windows:
VS 2019 Version 16.1.6
Dotnet Core 2.2.300

On Mac all the latest...

Is there a difference at your env?

SergejDK on 18 Jul 2019

Looks like there is a bug in ObservableCollection content comparsion. At first, we do not have any listview, only content view. At second pass, we have a listview, but do not have previous. And at third pass we memoize the list view and comparsion works as designed.

@vshapenko
did you debug into Fabulous.XamarinForms and it showed null? or is that what you think?

SergejDK on 18 Jul 2019

Looks like there is a bug in ObservableCollection content comparsion. At first, we do not have any listview, only content view. At second pass, we have a listview, but do not have previous. And at third pass we memoize the list view and comparsion works as designed.

@vshapenko
did you debug into Fabulous.XamarinForms and it showed null? or is that what you think?

That is my suggestion.

vshapenko on 19 Jul 2019

The sample code given by @vshapenko doesn't show the page on my armeabi-v7a Android emulator, instead the emulator is stuck on this:

Happypig375 on 19 Jul 2019

Logs

1>------ Build started: Project: NRE, Configuration: Debug Any CPU ------
1>NRE -> C:\Users\Admin\source\repos\NRE\NRE\bin\Debug\netstandard2.0\NRE.dll
2>------ Build started: Project: NRE.Android, Configuration: Debug Any CPU ------
2>      "C:\Users\Admin\source\repos\NRE\.nuget\NuGet.exe" install "C:\Users\Admin\source\repos\NRE\NRE.Android\packages.config" -source "https://www.nuget.org/api/v2/"  -NonInteractive -RequireConsent -solutionDir "C:\Users\Admin\source\repos\NRE"
2>      Restoring NuGet packages...
2>      To prevent NuGet from downloading packages during build, open the Visual Studio Options dialog, click on the NuGet Package Manager node and uncheck 'Allow NuGet to download missing packages'.
2>      Feeds used:
2>        C:\Users\Admin\.nuget\packages\
2>        https://www.nuget.org/api/v2/
2>      All packages listed in C:\Users\Admin\source\repos\NRE\NRE.Android\packages.config are already installed.
2>      No way to resolve conflict between "mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" and "mscorlib, Version=2.0.5.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e". Choosing "mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" arbitrarily.
2>C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Current\Bin\Microsoft.Common.CurrentVersion.targets(2106,5): warning MSB3277: Found conflicts between different versions of "System.Runtime" that could not be resolved.  These reference conflicts are listed in the build log when log verbosity is set to detailed.
2>      NRE.Android -> C:\Users\Admin\source\repos\NRE\NRE.Android\bin\Debug\NRE.Android.dll
2>      No way to resolve conflict between "mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" and "mscorlib, Version=2.0.5.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e". Choosing "mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" arbitrarily.
2>      C:\Program Files\Android\jdk\microsoft_dist_openjdk_1.8.0.25\bin\javac.exe -J-Dfile.encoding=UTF8 -d obj\Debug\android\bin\classes -classpath "C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\Common7\IDE\ReferenceAssemblies\Microsoft\Framework\MonoAndroid\v9.0\mono.android.jar;obj\Debug\lp\10\jl\android.arch.lifecycle.common.jar;obj\Debug\lp\11\jl\bin\classes.jar;obj\Debug\lp\12\jl\bin\classes.jar;obj\Debug\lp\13\jl\bin\classes.jar;obj\Debug\lp\15\jl\bin\classes.jar;obj\Debug\lp\16\jl\com.android.support.support-annotations.jar;obj\Debug\lp\17\jl\bin\classes.jar;obj\Debug\lp\18\jl\com.android.support.collections.jar;obj\Debug\lp\19\jl\bin\classes.jar;obj\Debug\lp\20\jl\bin\classes.jar;obj\Debug\lp\21\jl\bin\classes.jar;obj\Debug\lp\22\jl\bin\classes.jar;obj\Debug\lp\23\jl\bin\classes.jar;obj\Debug\lp\24\jl\bin\classes.jar;obj\Debug\lp\25\jl\bin\classes.jar;obj\Debug\lp\26\jl\bin\classes.jar;obj\Debug\lp\27\jl\bin\classes.jar;obj\Debug\lp\28\jl\bin\classes.jar;obj\Debug\lp\29\jl\bin\classes.jar;obj\Debug\lp\30\jl\bin\classes.jar;obj\Debug\lp\31\jl\bin\classes.jar;obj\Debug\lp\32\jl\bin\classes.jar;obj\Debug\lp\33\jl\bin\classes.jar;obj\Debug\lp\34\jl\bin\classes.jar;obj\Debug\lp\35\jl\bin\classes.jar;obj\Debug\lp\36\jl\bin\classes.jar;obj\Debug\lp\37\jl\bin\classes.jar;obj\Debug\lp\39\jl\bin\classes.jar;obj\Debug\lp\4\jl\formsviewgroup.jar;obj\Debug\lp\40\jl\bin\classes.jar;obj\Debug\lp\41\jl\bin\classes.jar;obj\Debug\lp\42\jl\bin\classes.jar;obj\Debug\lp\43\jl\bin\classes.jar;obj\Debug\lp\44\jl\bin\classes.jar;obj\Debug\lp\45\jl\bin\classes.jar;obj\Debug\lp\46\jl\bin\classes.jar;obj\Debug\lp\8\jl\android.arch.core.common.jar;obj\Debug\lp\9\jl\bin\classes.jar" -bootclasspath "C:\Program Files (x86)\Android\android-sdk\platforms\android-28\android.jar" -encoding UTF-8 "@C:\Users\Admin\AppData\Local\Temp\tmp1095.tmp" 
2>      C:\Program Files\Android\jdk\microsoft_dist_openjdk_1.8.0.25\bin\java.exe -Dfile.encoding=UTF8 -Xmx1G -jar "C:\Program Files (x86)\Android\android-sdk\build-tools\28.0.3\\lib\dx.jar" --dex --no-strict --input-list=C:\Users\Admin\AppData\Local\Temp\tmp2A68.tmp --output obj\Debug\android\bin 
3>Waiting for runtime checks to complete
Detecting installed packages
Detecting installed packages...
Removing old runtime
Removing old runtime: Mono.Android.DebugRuntime...

Happypig375 on 19 Jul 2019

@Happypig375
could you provide the configs of your emulator? Will try to recreate it.

That is my suggestion.

@vshapenko
allright, then I'll try something here to check this.

SergejDK on 19 Jul 2019

It's the same emulator from #492.

Happypig375 on 19 Jul 2019

Xamarin 16.1.0.545 (d16-1@db7c858e8)

Xamarin Designer 16.1.0.418 (remotes/origin/d16-1@5b958bb10)
Visual Studio extension to enable Xamarin Designer tools in Visual Studio.

Xamarin Templates 16.2.112 (4db4af4)
Xamarin.Android SDK 9.3.0.23 (HEAD/d0b48056f)
Xamarin.Android Reference Assemblies and MSBuild support.
Mono: mono/mono/2018-08@3a07bd426d3
Java.Interop: xamarin/java.interop/d16-1@5ddc3e3
LibZipSharp: grendello/LibZipSharp/d16-1@44de300
LibZip: nih-at/libzip/rel-1-5-1@b95cf3f
ProGuard: xamarin/proguard/master@905836d
SQLite: xamarin/sqlite/3.27.1@8212a2d
Xamarin.Android Tools: xamarin/xamarin-android-tools/d16-1@acabd26
Xamarin.iOS and Xamarin.Mac SDK 12.10.0.157 (6bd9475)
Xamarin.iOS and Xamarin.Mac Reference Assemblies and MSBuild support.

Mono version: 5.20.1 (by mono --version)

vshapenko on 19 Jul 2019

I meant sth. like this:

grafik
(not my current setup....)

Because if I just create a armeabi-v7a it still works. It is slow but it works. So mybe my configurations of the emulator is different.

SergejDK on 19 Jul 2019

Thanks for the information @vshapenko
Will look at it later today!

SergejDK on 19 Jul 2019

Happypig375 on 19 Jul 2019

👍1

@TimLariviere @SergejDK
Runs fine on redmi 4x and Nokia 8
Looks like it crashes on certain CPUs.

vshapenko on 19 Jul 2019

@TimLariviere @SergejDK @Happypig375
Small update. I have found a workaround. Following code works fine:

```fs let view (model: Model) dispatch =
View.ContentPage(
content=View.Grid(

           rowdefs=["auto";"*"],
           children =
               [
                 yield View.Button (text="SetFlag", command= (fun ()->dispatch Flag))
                 yield View.Label(text="Flag set",isVisible=(model.Flag)).GridRow(1)
                 yield View.ListView(items=([1..100]|>List.map (fun x->View.Label(text=string x))),isVisible=not model.Flag).GridRow(1)


               ]
               )
       )

```
Based on this, it looks like there are some issues with visual tree state if it is changed per same view. I think the safe way is to have whole visual tree all the time, and hide elements we do not need

Update : my main app still not working...

vshapenko on 19 Jul 2019

Additional info.
I am also getting following exception:

           Unable to update view:: System.InvalidCastException: Specified cast is not valid.
07-19 12:58:52.953 I/mono-stdout(27246):   at (wrapper castclass) System.Object.__castclass_with_cache(object,intptr,intptr)
07-19 12:58:52.953 I/mono-stdout(27246):   at Microsoft.FSharp.Core.LanguagePrimitives+IntrinsicFunctions.UnboxGeneric[T] (System.Object source) [0x00006] in <5c64a998dff9fae1a745038398a9645c>:0 
07-19 12:58:52.953 I/mono-stdout(27246):   at <StartupCode$Fabulous>.$ViewElement+Create@46-1[T].Invoke (Microsoft.FSharp.Core.FSharpValueOption`1[T] prev, Fabulous.ViewElement curr, System.Object target) [0x00000] in D:\a\1\s\src\Fabulous\ViewElement.fs:46 
07-19 12:58:52.953 I/mono-stdout(27246):   at Fabulous.ViewElement.UpdateIncremental (Fabulous.ViewElement prev, System.Object target) [0x00000] in D:\a\1\s\src\Fabulous\ViewElement.fs:85 
07-19 12:58:52.953 I/mono-stdout(27246):   at <StartupCode$Fabulous-XamarinForms>[email protected] (Fabulous.ViewElement prevChild, Fabulous.ViewElement newChild, Xamarin.Forms.View targetChild) [0x00000] in D:\a\1\s\Fabulous.XamarinForms\src\Fabulous.XamarinForms\Xamarin.Forms.Core.fs:5365 
07-19 12:58:52.953 I/mono-stdout(27246):   at Fabulous.XamarinForms.Converters.updateCollectionGeneric$cont@148[T,TargetT] (Microsoft.FSharp.Core.FSharpValueOption`1[T] prevCollOpt, System.Collections.Generic.IList`1[T] targetColl, Microsoft.FSharp.Core.FSharpFunc`2[T,TResult] create, Microsoft.FSharp.Core.FSharpFunc`2[T,TResult] attach, Microsoft.FSharp.Core.FSharpFunc`2[T,TResult] canReuse, Microsoft.FSharp.Core.FSharpFunc`2[T,TResult] update, T[] coll, Microsoft.FSharp.Core.Unit unitVar) [0x0010e] in D:\a\1\s\Fabulous.XamarinForms\src\Fabulous.XamarinForms.Core\ViewConverters.fs:172 
07-19 12:58:52.953 I/mono-stdout(27246):   at Fabulous.XamarinForms.Converters.updateCollectionGeneric[T,TargetT] (Microsoft.FSharp.Core.FSharpValueOption`1[T] prevCollOpt, Microsoft.FSharp.Core.FSharpValueOption`1[T] collOpt, System.Collections.Generic.IList`1[T] targetColl, Microsoft.FSharp.Core.FSharpFunc`2[T,TResult] create, Microsoft.FSharp.Core.FSharpFunc`2[T,TResult] attach, Microsoft.FSharp.Core.FSharpFunc`2[T,TResult] canReuse, Microsoft.FSharp.Core.FSharpFunc`2[T,TResult] update) [0x00060] in D:\a\1\s\Fabulous.XamarinForms\src\Fabulous.XamarinForms.Core\ViewConverters.fs:144 
07-19 12:58:52.953 I/mono-stdout(27246):   at Fabulous.XamarinForms.ViewBuilders.UpdateGrid (Microsoft.FSharp.Core.FSharpValueOption`1[T] prevOpt, Fabulous.ViewElement curr, Xamarin.Forms.Grid target) [0x00460] in D:\a\1\s\Fabulous.XamarinForms\src\Fabulous.XamarinForms\Xamarin.Forms.Core.fs:5328 
07-19 12:58:52.953 I/mono-stdout(27246):   at <StartupCode$Fabulous-XamarinForms>[email protected] (Microsoft.FSharp.Core.FSharpValueOption`1[T] prevOpt, Fabulous.ViewElement curr, Xamarin.Forms.Grid target) [0x00000] in D:\a\1\s\Fabulous.XamarinForms\src\Fabulous.XamarinForms\Xamarin.Forms.Core.fs:5266 
07-19 12:58:52.953 I/mono-stdout(27246):   at Fabulous.ViewElement.UpdateIncremental (Fabulous.ViewElement prev, System.Object target) [0x00000] in D:\a\1\s\src\Fabulous\ViewElement.fs:85 
07-19 12:58:52.953 I/mono-stdout(27246):   at Fabulous.XamarinForms.ViewBuilders.UpdateContentPage (Microsoft.FSharp.Core.FSharpValueOption`1[T] prevOpt, Fabulous.ViewElement curr, Xamarin.Forms.ContentPage target) [0x00234] in D:\a\1\s\Fabulous.XamarinForms\src\Fabulous.XamarinForms\Xamarin.Forms.Core.fs:12621 
07-19 12:58:52.953 I/mono-stdout(27246):   at <StartupCode$Fabulous-XamarinForms>[email protected] (Microsoft.FSharp.Core.FSharpValueOption`1[T] prevOpt, Fabulous.ViewElement curr, Xamarin.Forms.ContentPage target) [0x00000] in D:\a\1\s\Fabulous.XamarinForms\src\Fabulous.XamarinForms\Xamarin.Forms.Core.fs:12593 
07-19 12:58:52.953 I/mono-stdout(27246):   at Fabulous.ViewElement.UpdateIncremental (Fabulous.ViewElement prev, System.Object target) [0x00000] in D:\a\1\s\src\Fabulous\ViewElement.fs:85 
07-19 12:58:52.953 I/mono-stdout(27246):   at Fabulous.XamarinForms.Converters.updateNavigationPages$cont@422 (Microsoft.FSharp.Core.FSharpValueOption`1[T] prevCollOpt, Xamarin.Forms.NavigationPage target, Microsoft.FSharp.Core.FSharpFunc`2[T,TResult] attach, Fabulous.ViewElement[] coll, Microsoft.FSharp.Core.Unit unitVar) [0x00210] in D:\a\1\s\Fabulous.XamarinForms\src\Fabulous.XamarinForms.Core\ViewConverters.fs:455 
07-19 12:58:52.953 I/mono-stdout(27246):   at Fabulous.XamarinForms.Converters.updateNavigationPages (Microsoft.FSharp.Core.FSharpValueOption`1[T] prevCollOpt, Microsoft.FSharp.Core.FSharpValueOption`1[T] collOpt, Xamarin.Forms.NavigationPage target, Microsoft.FSharp.Core.FSharpFunc`2[T,TResult] attach) [0x00062] in D:\a\1\s\Fabulous.XamarinForms\src\Fabulous.XamarinForms.Core\ViewConverters.fs:418 
07-19 12:58:52.953 I/mono-stdout(27246):   at Fabulous.XamarinForms.ViewBuilders.UpdateNavigationPage (Microsoft.FSharp.Core.FSharpValueOption`1[T] prevOpt, Fabulous.ViewElement curr, Xamarin.Forms.NavigationPage target) [0x00334] in D:\a\1\s\Fabulous.XamarinForms\src\Fabulous.XamarinForms\Xamarin.Forms.Core.fs:11983 
07-19 12:58:52.953 I/mono-stdout(27246):   at <StartupCode$Fabulous-XamarinForms>[email protected] (Microsoft.FSharp.Core.FSharpValueOption`1[T] prevOpt, Fabulous.ViewElement curr, Xamarin.Forms.NavigationPage target) [0x00000] in D:\a\1\s\Fabulous.XamarinForms\src\Fabulous.XamarinForms\Xamarin.Forms.Core.fs:11935 
07-19 12:58:52.953 I/mono-stdout(27246):   at Fabulous.ProgramRunner`3[arg,model,msg].updateView (model updatedModel) [0x00072] in D:\a\1\s\src\Fabulous\Program.fs:91 
07-19 12:58:52.953 I/mono-stdout(27246):   at Fabulous.ProgramRunner`3[arg,model,msg].processMsg (msg msg) [0x0002e] in D:\a\1\s\src\Fabulous\Program.fs:66

vshapenko on 19 Jul 2019

Got my main app to work with fix provided above plus disabling skiasharp control on page

vshapenko on 19 Jul 2019

@Happypig375
I use the same emulator.....

SergejDK on 19 Jul 2019

@vshapenko
the versions looking good to me. using the same stuff.....
I'll try to find a phone where the NRE is happening...

Sorry for the bug....

SergejDK on 19 Jul 2019

@vshapenko
Your example created the error from #492 which @Happypig375 discovered on antoher device (Motorola G6) maybe your issue and the one from @Happypig375 are related.

Will try to identify what is happenend here that makes this stuff go crazy.

SergejDK on 19 Jul 2019

👍3

@SergejDK i would like to help, but for now i do not have much knowledge about fabulous internals.

vshapenko on 19 Jul 2019

@vshapenko
do you have VS 2017 installed or only 2019?

SergejDK on 21 Jul 2019

@SergejDK only vs 2019, but also rider

vshapenko on 21 Jul 2019

Even something as simple as

open Fabulous.Core
open Fabulous.DynamicViews
open Xamarin.Forms

module App = 
    let program = Program.mkSimple id (fun () -> id) (fun _ _ -> View.ContentPage(View.Button "Hi~"))

type App () as app = 
    inherit Application ()

    let runner = 
        App.program
        |> Program.withErrorHandler (fun (msg, exn) -> System.Diagnostics.Debug.WriteLine exn
                                                       System.Diagnostics.Debugger.Break())
        |> Program.runWithDynamicView app

Throws an NRE on startup on my Xiaomi Redmi 6. The emulators cannot reproduce this.