Design and Architecture

public interface IWidget
{
    // Methods...
 
    // Properties...
 
    int Count
    {
        get;
        set;
    }
}

public abstract Widget : IWidget
{
    private int count = 0;
 
    public int Count
    {
        get
        {
            return count;
        }
        set
        {
            count = value;
        }
    }
}

public class MyWidget : Widget
{
    public override int Count
    {
        get
        {
            return base.Count;
        }
        set
        {
            base.Count = value;
 
            // Do stuff based on new count value...
        }
    }
}

public class Counter
{
    private int count = 0;
 
    public event EventHandler CountChanged;
 
    // ...
 
    public int Count
    {
        get
        {
            return count;
        }
        set
        {
            if(count < 0)
            {
                throw new ArgumentOutOfRange("Count");
            }
 
            count = value;
 
            OnCountChanged(EventArgs.Empty);
        }
    }
}

Counter myCounter = new Counter();
 
IWidget widget1 = new MyFirstWidget(myCounter);
IWidget widget2 = new MySecondWidget(myCounter);

foreach(IWidget widget in widgets)
{
    widget.Count++;
}

myCounter.Count++;