Crash when deleting a realm object bound to a ListView

Question

I have a Xamarin XAML page with a ListView. The list data source is linked to an observable collection which is populated with realm objects.

When i try to delete an object from the ListView (first from the data source and then from realm) I've got the crash.

The crash occurs later at binding time only on iOS and the inner exception message is:

This object is detached. Was it deleted from the realm?

So, it seems that the object is still accessed from the ListView after deletion.

StackTrace:

  at System.Reflection.MonoMethod.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00050] in /Users/builder/data/lanes/3818/3983064a/source/xamarin-macios/_ios-build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/mcs/class/corlib/System.Reflection/MonoMethod.cs:313 
  at System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) [0x00000] in /Users/builder/data/lanes/3818/3983064a/source/xamarin-macios/_ios-build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/mcs/class/referencesource/mscorlib/system/reflection/methodbase.cs:229 
  at Xamarin.Forms.BindingExpression+BindingExpressionPart.TryGetValue (System.Object source, System.Object& value) [0x00043] in C:\BuildAgent\work\aad494dc9bc9783\Xamarin.Forms.Core\BindingExpression.cs:498 
  at Xamarin.Forms.BindingExpression.Unapply () [0x00030] in C:\BuildAgent\work\aad494dc9bc9783\Xamarin.Forms.Core\BindingExpression.cs:90 
  at Xamarin.Forms.Binding.Unapply () [0x0000e] in C:\BuildAgent\work\aad494dc9bc9783\Xamarin.Forms.Core\Binding.cs:142 
  at Xamarin.Forms.BindableObject.ApplyBindings (System.Object oldContext, System.Boolean skipBindingContext) [0x0002e] in C:\BuildAgent\work\aad494dc9bc9783\Xamarin.Forms.Core\BindableObject.cs:407 
  at Xamarin.Forms.BindableObject.ApplyBindings (System.Object oldContext) [0x00000] in C:\BuildAgent\work\aad494dc9bc9783\Xamarin.Forms.Core\BindableObject.cs:123 
  at Xamarin.Forms.BindableObject.SetInheritedBindingContext (Xamarin.Forms.BindableObject bindable, System.Object value) [0x0005a] in C:\BuildAgent\work\aad494dc9bc9783\Xamarin.Forms.Core\BindableObject.cs:117 
  at Xamarin.Forms.Element.SetChildInheritedBindingContext (Xamarin.Forms.Element child, System.Object context) [0x00000] in C:\BuildAgent\work\aad494dc9bc9783\Xamarin.Forms.Core\Element.cs:472 
  at Xamarin.Forms.Element.OnBindingContextChanged () [0x00021] in C:\BuildAgent\work\aad494dc9bc9783\Xamarin.Forms.Core\Element.cs:322 
  at Xamarin.Forms.View.OnBindingContextChanged () [0x00042] in C:\BuildAgent\work\aad494dc9bc9783\Xamarin.Forms.Core\View.cs:99 
  at Xamarin.Forms.BindableObject.SetInheritedBindingContext (Xamarin.Forms.BindableObject bindable, System.Object value) [0x00061] in C:\BuildAgent\work\aad494dc9bc9783\Xamarin.Forms.Core\BindableObject.cs:118 
  at Xamarin.Forms.Element.SetChildInheritedBindingContext (Xamarin.Forms.Element child, System.Object context) [0x00000] in C:\BuildAgent\work\aad494dc9bc9783\Xamarin.Forms.Core\Element.cs:472 
  at Xamarin.Forms.Element.OnBindingContextChanged () [0x00021] in C:\BuildAgent\work\aad494dc9bc9783\Xamarin.Forms.Core\Element.cs:322 
  at Xamarin.Forms.View.OnBindingContextChanged () [0x00042] in C:\BuildAgent\work\aad494dc9bc9783\Xamarin.Forms.Core\View.cs:99 
  at Xamarin.Forms.Grid.OnBindingContextChanged () [0x00006] in C:\BuildAgent\work\aad494dc9bc9783\Xamarin.Forms.Core\Grid.cs:139 
  at Xamarin.Forms.BindableObject.SetInheritedBindingContext (Xamarin.Forms.BindableObject bindable, System.Object value) [0x00061] in C:\BuildAgent\work\aad494dc9bc9783\Xamarin.Forms.Core\BindableObject.cs:118 
  at Xamarin.Forms.Element.SetChildInheritedBindingContext (Xamarin.Forms.Element child, System.Object context) [0x00000] in C:\BuildAgent\work\aad494dc9bc9783\Xamarin.Forms.Core\Element.cs:472 
  at Xamarin.Forms.Element.OnBindingContextChanged () [0x00021] in C:\BuildAgent\work\aad494dc9bc9783\Xamarin.Forms.Core\Element.cs:322 
  at Xamarin.Forms.View.OnBindingContextChanged () [0x00042] in C:\BuildAgent\work\aad494dc9bc9783\Xamarin.Forms.Core\View.cs:99 
  at Xamarin.Forms.Grid.OnBindingContextChanged () [0x00006] in C:\BuildAgent\work\aad494dc9bc9783\Xamarin.Forms.Core\Grid.cs:139 
  at Xamarin.Forms.BindableObject.SetInheritedBindingContext (Xamarin.Forms.BindableObject bindable, System.Object value) [0x00061] in C:\BuildAgent\work\aad494dc9bc9783\Xamarin.Forms.Core\BindableObject.cs:118 
  at Xamarin.Forms.Element.SetChildInheritedBindingContext (Xamarin.Forms.Element child, System.Object context) [0x00000] in C:\BuildAgent\work\aad494dc9bc9783\Xamarin.Forms.Core\Element.cs:472 
  at Xamarin.Forms.Element.OnBindingContextChanged () [0x00021] in C:\BuildAgent\work\aad494dc9bc9783\Xamarin.Forms.Core\Element.cs:322 
  at Xamarin.Forms.Cell.OnBindingContextChanged () [0x00000] in C:\BuildAgent\work\aad494dc9bc9783\Xamarin.Forms.Core\Cells\Cell.cs:117 
  at Xamarin.Forms.BindableObject.BindingContextPropertyBindingPropertyChanged (Xamarin.Forms.BindableObject bindable, System.Object oldvalue, System.Object newvalue) [0x0001b] in C:\BuildAgent\work\aad494dc9bc9783\Xamarin.Forms.Core\BindableObject.cs:429 
  at Xamarin.Forms.BindableObject.SetValueActual (Xamarin.Forms.BindableProperty property, Xamarin.Forms.BindableObject+BindablePropertyContext context, System.Object value, System.Boolean currentlyApplying, Xamarin.Forms.BindableObject+SetValueFlags attributes, System.Boolean silent) [0x00108] in C:\BuildAgent\work\aad494dc9bc9783\Xamarin.Forms.Core\BindableObject.cs:584 
  at Xamarin.Forms.BindableObject.SetValueCore (Xamarin.Forms.BindableProperty property, System.Object value, Xamarin.Forms.BindableObject+SetValueFlags attributes, Xamarin.Forms.BindableObject+SetValuePrivateFlags privateAttributes) [0x0014b] in C:\BuildAgent\work\aad494dc9bc9783\Xamarin.Forms.Core\BindableObject.cs:378 
  at Xamarin.Forms.BindableObject.SetValue (Xamarin.Forms.BindableProperty property, System.Object value, System.Boolean fromStyle, System.Boolean checkAccess) [0x0005f] in C:\BuildAgent\work\aad494dc9bc9783\Xamarin.Forms.Core\BindableObject.cs:531 
  at Xamarin.Forms.BindableObject.SetValue (Xamarin.Forms.BindableProperty property, System.Object value) [0x00000] in C:\BuildAgent\work\aad494dc9bc9783\Xamarin.Forms.Core\BindableObject.cs:83 
  at Xamarin.Forms.BindableObject.set_BindingContext (System.Object value) [0x00000] in C:\BuildAgent\work\aad494dc9bc9783\Xamarin.Forms.Core\BindableObject.cs:24 
  at Xamarin.Forms.TemplatedItemsList`2+<UnhookItem>d__153[TView,TItem].MoveNext () [0x000a7] in C:\BuildAgent\work\aad494dc9bc9783\Xamarin.Forms.Core\TemplatedItemsList.cs:1210

InnerException StackTrace:

  at Realms.NativeException.ThrowIfNecessary (System.Func`2[T,TResult] overrider) [0x00014] in <fb8acf22c75e4f8ba1fe5f730039e63b>:0 
  at Realms.RowHandle.get_RowIndex () [0x00009] in <fb8acf22c75e4f8ba1fe5f730039e63b>:0 
  at Realms.RealmObject.GetObjectValue[T] (System.String propertyName) [0x00000] in <fb8acf22c75e4f8ba1fe5f730039e63b>:0 
  at TestProject.StockApp.Data.ManagedObjects.ArticleEntity.get_Article () [0x00006] in <bc12041acc564a39b37d8658934e3bc3>:0 
  at (wrapper managed-to-native) System.Reflection.MonoMethod:InternalInvoke (System.Reflection.MonoMethod,object,object[],System.Exception&)
  at System.Reflection.MonoMethod.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00038] in /Users/builder/data/lanes/3818/3983064a/source/xamarin-macios/_ios-build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/mcs/class/corlib/System.Reflection/MonoMethod.cs:305

Update

It seems that the error occurs only when the Realm objects used in the ListView have relationships that were also displayed to the ListView cell.

For example, if I have a list of Dogs but in the cell I also show the Owner .FirstName then the crash occurs when I delete the selected dog item.

public class Dog : RealmObject 
{
    public string Name { get; set; }
    public int Age { get; set; }
    public Person Owner { get; set; }
}

public class Person: RealmObject 
{
    public string FirstName{ get; set; }
}

score 1 · Accepted Answer · answered Sep 28 '16 at 10:42

1

The list data source is linked to an observable collection which is populated with realm objects

How is that observable collection updated?

The stack trace is deep in Forms - looks like it is a quirk of how their code works - can you please send source to support@realm.io and I will look at it.

answered Sep 28 '16 at 10:42

Andy Dent

17,578
6
88
115

The collection is instantiated in the ViewModel constructor, i.e: 'ArticleList = new ObservableCollection(Realm.All().AsEnumerable())'. Then on the delete command I remove the object from the list and then from the Realm. – Trasnea Daniel Sep 28 '16 at 13:01
I have sent you the test project – Trasnea Daniel Oct 18 '16 at 06:36
This seems to be a combination of Realm and Xamarin.Forms internal workings. The workaround is to proxy desired relationship properties to the parent object, e.g. `Dog.OwnerName => Dog.Owner.Name`. I've opened an [issue on Github](https://github.com/realm/realm-dotnet/issues/883) to track the bug and provide a more permanent solution. – Nikola Irinchev Oct 24 '16 at 14:15

score 0 · Answer 2 · answered Jun 24 '17 at 23:55

0

As of v0.81.0, RealmObject is implicitly an ObservableObject such that it fires INotifyPropertyChanged on properties and INotifyCollectionChanged on IList and IQueryable properties.

For more info:

answered Jun 24 '17 at 23:55

Korayem

12,108
5
69
56

Crash when deleting a realm object bound to a ListView

Update

2 Answers2