Notify One object when a property of another object changes

Question

I have a parent object called Page that has a List of objects called Control:

public class Page
{
   List controls {get;set;}
}

Answer 1

public class CustomControl : INotifyPropertyChanged
{
    private string _name;
    public string Name
    {
        get { return _name; }
        set
        {
            if (_name == value) return;
            _name = value;
            PropertyChanged(this, new PropertyChangedEventArgs("Name"));
        }
    }

    private string _value;
    public string Value
    {
        get { return _value; }
        set
        {
            if (_value == value) return;

            _value = value;
            PropertyChanged(this, new PropertyChangedEventArgs("Value"));
        }
    }

    public event PropertyChangedEventHandler PropertyChanged = delegate { };

    internal virtual void OnSiblingInPagePropertyChanged(object sender, PropertyChangedEventArgs args)
    {

    }
}

public class CustomControlObservableColletion : ObservableCollection
{
    // Required because, by default, it is not possible to find out which items
    // have been cleared when the CollectionChanged event is fired after a .Clear() call.
    protected override void ClearItems()
    {
        foreach (var item in Items.ToList())
            Remove(item);
    }

}

public class Page
{
    public IList Controls { get; private set; }

    public Page()
    {
        var controls = new CustomControlObservableColletion();
        controls.CollectionChanged += OnCollectionChanged;
        Controls = controls;
    }

    private void OnCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        switch (e.Action)
        {
            case NotifyCollectionChangedAction.Add:
                RegisterControls(e.NewItems);
                break;

            case NotifyCollectionChangedAction.Replace:
                RegisterControls(e.NewItems);
                DeRegisterControls(e.OldItems);
                break;

            case NotifyCollectionChangedAction.Remove:
                DeRegisterControls(e.OldItems);
                break;
        }
    }

    private void RegisterControls(IList controls)
    {
        foreach (CustomControl control in controls)
            control.PropertyChanged += OnControlPropertyChanged;
    }

    private void DeRegisterControls(IList controls)
    {
        foreach (CustomControl control in controls)
            control.PropertyChanged -= OnControlPropertyChanged;
    }

    private void OnControlPropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        foreach (var control in Controls.Where(c => c != sender))
            control.OnSiblingInPagePropertyChanged(sender, e);
    }
}