Object not holding instance when accessed through method

I made a Model Class "RestaurentList" which populates two collections with data from a json file. After instantiating an object to the class in my ViewModel i databind the collections to an ItemsControl.

Everything in the above works fine, but when i call the method populatePartialList from the object in my ViewModel, it doesn't contain any of the data from when i instantiated the object. This means, that when my method tries to repopulate the PartialList, it can't because it doesn't find the data from FullList.

Edit: I left out some of the code as you can see with the comment tags. I just want to give you an understanding of how i am doing this.

My question basicly is, why the object doesn't contain any data when i'm calling the method populatePartialList.

My guess it's got something to do with the fact, that i am databinding the List to an ItemsControl and therefor can't access it anymore? What should do in that case then? I'm trying to make a very simple pagination

Edit to the above; I tried removing my Bind and i still can't reach the data.

Model:

public class RestaurentList
    {
        private ObservableCollection<Restaurent> _fullList = new ObservableCollection<Restaurent>();

        private ObservableCollection<Restaurent> _partialList = new ObservableCollection<Restaurent>();

        public ObservableCollection<Restaurent> FullList
        {
            get { return _fullList; }
        }

        public ObservableCollection<Restaurent> PartialList
        {
            get { return _partialList; }
        }

        public RestaurentList()
        {
            populateList();
        }

        public void populatePartialList(int fromValue = 1)
        {
            int collectionAmount = _fullList.Count;
            int itemsToShow = 2;
            fromValue = (fromValue > collectionAmount ? 1 : fromValue);

            foreach (Restaurent currentRestaurent in _fullList)
            {
                int currentId = Convert.ToInt32(currentRestaurent.UniqueId);
                if (currentId == fromValue || (currentId > fromValue && currentId <= (fromValue + itemsToShow)-1))
                {
                    _partialList.Add(currentRestaurent);
                }
            }
        } 

        private async void populateList()
        {
            // Get json data

            foreach (JsonValue restaurentValue in jsonArray)
            {
                // populate full list

                foreach (JsonValue menuValue in restaurentObject["Menu"].GetArray())
                {
                    // populate full list
                }
                this._fullList.Add(restaurent);
            }
            populatePartialList();
        }

        public override string ToString()
        {
            // Code
        }
    }

View Model:

class ViewModelDefault : INotifyPropertyChanged
    {


        private RestaurentList _list;

        public ObservableCollection<Restaurent> List
        {
            get { return _list.PartialList; }
        }


        public ViewModelDefault()
        {  
            _list = new RestaurentList();
            _list.populatePartialList(2); // This is where i don't see the data from RestaurentList
        }

        #region Notify
    }

Edit for Jon:

public RestaurentList()
        {
            PopulatePartialList();
        }

        public async void PopulatePartialList(int fromValue = 1)
        {
            await PopulateList();
            int collectionAmount =  _fullList.Count;
            int itemsToShow = 2;
            fromValue = (fromValue > collectionAmount ? 1 : fromValue);

            foreach (Restaurent currentRestaurent in _fullList)
            {
                int currentId = Convert.ToInt32(currentRestaurent.UniqueId);
                if (currentId == fromValue || (currentId > fromValue && currentId <= (fromValue + itemsToShow)-1))
                {
                    _partialList.Add(currentRestaurent);
                }
            }
        } 

        private async Task PopulateList()
        {
}