WeakSubscribe in MvvmCross doesn't work correct

Question

Context:

I have an unknown Model-Object which contains one or more ObservableCollections. These collections contains objects which implements INotifyPropertyChanged. I now want to observe the PropertyChangedEvents for all objects inside the Model-Object.

What I have done:

So I wrote this method which uses reflection to find the specific objects. This all works fine. Except the part where it comes to the MvvmCross function WeakSubscribe. I really like the idea behind, but it seems it loses the reference and don't fire the event.

Strange: If I debug this code it works correct, but without breakpoints it's not working.

    private void SubscribeToDetailData()
    {
        var tempTokenList = new List<MvxNotifyPropertyChangedEventSubscription>();

        var fieldInfos =
            DetailData.GetType().GetRuntimeProperties().Where(f => Helpers.IsSubclassOfRawGeneric(typeof (ObservableCollection<>), f.PropertyType));

        foreach (var fieldInfo in fieldInfos)
        {
            var collection = fieldInfo.GetValue(DetailData) as IEnumerable<object>;
            if (collection == null) 
                continue;

            foreach (var inpc in collection.Cast<INotifyPropertyChanged>())
            {
                tempTokenList.Add(inpc.WeakSubscribe((sender, e) =>  DetailDataPropertyChanged(e.PropertyName))); 
            }
        }
        _subscriptionTokens = tempTokenList.ToArray();
    }

    // This method is never raised
    private void DetailDataPropertyChanged(string propertyName)
    {
        
        if (_enabledFields.Evaluate(DetailData, propertyName))
             RaisePropertyChanged(() => FieldEnabledState);
    }

Answer 1

It might be that your subscribed Action is getting garbage collected.

This can be caused, I think, if the compiler creates an instance of an anonymous class to implement your anonymous Action. I wouldn't normally expect this to happen in your code because you are not using any local variables in your Action - but this could be the case.

Does your code work if you change the subscription to:

tempTokenList.Add(inpc.WeakSubscribe(DetailDataPropertyChanged)); 

with the method signature changed to:

private void DetailDataPropertyChanged(object sender, PropertyChangedEventArgs e)