ObservableCollection not noticing when Item in it changes (even with INotifyPropertyChanged)

Question

Does anyone know why this code doesn\'t work:

public class CollectionViewModel : ViewModelBase {  
    public ObservableCollection Con         


        

Answer 1

The ContentList's Set method will not get called when you change a value inside the collection, instead you should be looking out for the CollectionChanged event firing.

public class CollectionViewModel : ViewModelBase
{          
    public ObservableCollection ContentList
    {
        get { return _contentList; }
    }

    public CollectionViewModel()
    {
         _contentList = new ObservableCollection();
         _contentList.CollectionChanged += ContentCollectionChanged;
    }

    public void ContentCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        //This will get called when the collection is changed
    }
}

---

Okay, that's twice today I've been bitten by the MSDN documentation being wrong. In the link I gave you it says:

Occurs when an item is added, removed, changed, moved, or the entire list is refreshed.

But it actually doesn't fire when an item is changed. I guess you'll need a more bruteforce method then:

public class CollectionViewModel : ViewModelBase
{          
    public ObservableCollection ContentList
    {
        get { return _contentList; }
    }

    public CollectionViewModel()
    {
         _contentList = new ObservableCollection();
         _contentList.CollectionChanged += ContentCollectionChanged;
    }

    public void ContentCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        if (e.Action == NotifyCollectionChangedAction.Remove)
        {
            foreach(EntityViewModel item in e.OldItems)
            {
                //Removed items
                item.PropertyChanged -= EntityViewModelPropertyChanged;
            }
        }
        else if (e.Action == NotifyCollectionChangedAction.Add)
        {
            foreach(EntityViewModel item in e.NewItems)
            {
                //Added items
                item.PropertyChanged += EntityViewModelPropertyChanged;
            }     
        }       
    }

    public void EntityViewModelPropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        //This will get called when the property of an object inside the collection changes
    }
}

If you are going to need this a lot you may want to subclass your own ObservableCollection that triggers the CollectionChanged event when a member triggers its PropertyChanged event automatically (like it says it should in the documentation...)