Question

I have a collection with thousands of nodes. I’d like each node to fire a Changed() event to notify the container.

Normally, registering an event creates a new EventHandler<>:

Node node = new Node();
node.Changed += new EventHandler<EventArgs>(OnChanged);

This would result in thousands of EventHandler<> objects.

I’d like to know if it is possible to construct a single EventHandler<> and use it simultaneously with thousands of nodes:

class Container {
    EventHandler<EventArgs> eventHandler = 
      new EventHandler<EventArgs>(OnChanged);

  void CreateNode() {
    Node node = new Node();
    node.Changed += eventHandler;
  }
}

Answer 1

Yes, you can: Reference the System.Collections.ObjectModel.ObservableCollection<T> as described on MSDN: http://msdn.microsoft.com/en-us/library/ms668604.aspx

Here is a sample class that notifies when it’s properties are changed:

public class Person : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    private string firstName
    public string FirstName
    {
        get { return this.firstName; }
        set 
        {
            if( this.firstName == value )
            {
                return;
            }

            this.firstName = value;
            this.RaisePropertyChanged("FirstName");

        }
    } 

    private void RaisePropertyChanged(string propertyName)
    {
       if( this.PropertyChanged != null )
       {
           this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
       }
    }
}

Then use the System.Collections.ObjectModel.ObservableCollection<T> because it fires the following events:

`CollectionChanged` - Occurs when an item is added, removed, changed, moved, or the entire list is refreshed

`PropertyChanged` - Also an implementation of INotifyPropertyChanged inteface, which fires when the collection's own properties change.