Does an ObservableCollection Exist That Tracks Both Collection and Element Property Changes?

ObservableCollection that monitors collection and element attribute changes

Question:

Is there a collection that can simultaneously monitor changes in the collection itself and changes in the attributes of its elements?

Solution:

If no ready-made collection meets this requirement, you can create an implementation that extends ObservableCollection to monitor its elements for PropertyChanged events.

Implementation:

The following is an example implementation of ObservableCollectionEx that implements this functionality:

<code class="language-csharp">public class ObservableCollectionEx<T> : ObservableCollection<T> where T : INotifyPropertyChanged
{
    protected override void OnCollectionChanged(NotifyCollectionChangedEventArgs e)
    {
        Unsubscribe(e.OldItems);
        Subscribe(e.NewItems);
        base.OnCollectionChanged(e);
    }

    protected override void ClearItems()
    {
        foreach (T element in this)
            element.PropertyChanged -= ContainedElementChanged;

        base.ClearItems();
    }

    private void Subscribe(IList iList)
    {
        if (iList != null)
        {
            foreach (T element in iList)
                element.PropertyChanged += ContainedElementChanged;
        }
    }

    private void Unsubscribe(IList iList)
    {
        if (iList != null)
        {
            foreach (T element in iList)
                element.PropertyChanged -= ContainedElementChanged;
        }
    }

    private void ContainedElementChanged(object sender, PropertyChangedEventArgs e)
    {
        OnPropertyChanged(new PropertyChangedEventArgs(e.PropertyName)); //Corrected this line.
    }
}</code>

Usage:

Use ObservableCollection like a normal ObservableCollectionEx, but convert it to a INotifyPropertyChanged to subscribe to its element's property change events:

<code class="language-csharp">ObservableCollectionEx<Element> collection = new ObservableCollectionEx<Element>();
((INotifyPropertyChanged)collection).PropertyChanged += (x, y) => ReactToChange();</code>

Note: In the ContainedElementChanged method, the parameter of OnPropertyChanged needs to be a new PropertyChangedEventArgs instance instead of using e directly. This has been corrected in the code above. This ensures that the correct property name is passed to the event handler.

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