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List With Events

, 6 Dec 2008
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An extended List that fires events when the count of list-items changes

Introduction

List<T> provides no events when the count of the list-items is changed. This article provides a class that notifies with a event when the number of the elements is changed.

The class provides a basic approach to this. Further members can be added if needed.

Using the Code

An example will show the usage of this class:

using System;
using gfoidl.Tools;

namespace ConsoleApplication1
{
	class Program
	{
		static void Main()
		{
			gfList<int> list = new gfList<int>();
			list.CountChanged += 
				new EventHandler<gfList<int>.ListEventArgs>
					(list_CountChanged);

			list.Add(1);
			list.AddRange(new int[] { 2, 3, 4, 5 });
			list.Remove(3);
			list.Clear();

			Console.ReadKey();
		}

		private static void list_CountChanged(
			object sender, 
			gfList<int>.ListEventArgs e)
		{
			Console.WriteLine(e.Count);
		}
	}
}

Implementation

using System;
using System.Collections.Generic;

namespace gfoidl.Tools
{
	/// <summary>
	/// Extended list with events
	/// </summary>
	/// <typeparam name="T">
	/// The type of the elements
	/// </typeparam>
	public class gfList<T> : List<T>
	{
		#region Event(s)
		public event EventHandler<ListEventArgs> CountChanged;
		#endregion
		//---------------------------------------------------------------
		#region Methods
		/// <summary>
		/// Adds an item
		/// </summary>
		public new void Add(T item)
		{
			base.Add(item);

			// Copy to a temporary variable to be thread-safe (MSDN).
			EventHandler<ListEventArgs> tmp = CountChanged;
			if (tmp != null)
			    tmp(this, new gfList<T>.ListEventArgs(this.Count));
		}
		//------------------------------------------------------------------
		/// <summary>
		/// Adds a range
		/// </summary>
		public new void AddRange(IEnumerable<T> collection)
		{
			base.AddRange(collection);

			// Copy to a temporary variable to be thread-safe (MSDN).
			EventHandler<ListEventArgs> tmp = CountChanged;
			if (tmp != null)
			    tmp(this, new gfList<T>.ListEventArgs(this.Count));
		}
		//------------------------------------------------------------------
		/// <summary>
		/// Clears the list.
		/// </summary>
		public new void Clear()
		{
			base.Clear();

			// Copy to a temporary variable to be thread-safe (MSDN).
			EventHandler<ListEventArgs> tmp = CountChanged;
			if (tmp != null)
			    tmp(this, new gfList<T>.ListEventArgs(this.Count));
		}
		//------------------------------------------------------------------
		/// <summary>
		/// Removes the first matched item.
		/// </summary>
		public new void Remove(T item)
		{
			base.Remove(item);

			// Copy to a temporary variable to be thread-safe (MSDN).
			EventHandler<ListEventArgs> tmp = CountChanged;
			if (tmp != null)
			    tmp(this, new gfList<T>.ListEventArgs(this.Count));
		}
		#endregion
		//------------------------------------------------------------------
		#region Subclasses
		/// <summary>
		/// EventArgs
		/// </summary>
		public class ListEventArgs : EventArgs
		{
			/// <summary>
			/// Number of elements in the list
			/// </summary>
			public int Count { get; set; }
			//----------------------------------------------------------
			public ListEventArgs(int anzahl)
			{
				this.Count = anzahl;
			}
		}
		#endregion
	}
}

History

  • 6th December, 2008: Initial release

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

About the Author

Günther M. FOIDL
Software Developer (Senior) Foidl Günther
Austria Austria
Engineer in combustion engine development.
Programming languages: C#, FORTRAN 95, Matlab
 
FIS-overall worldcup winner in Speedski (Downhill) 2008/09 and 2009/10.

Comments and Discussions

 
GeneralMy vote of 5 Pinmembermanoj kumar choubey26-Feb-12 21:31 
GeneralFor when you only want to know if a list is modified: Pinmembertonyt23-Dec-08 5:48 
GeneralRe: For when you only want to know if a list is modified: PinmemberGünther M. FOIDL19-Jun-09 3:12 
GeneralSimple Solution, but there are issues with using Hiding as the Implementation PinmemberJason Smith - FMR10-Dec-08 3:42 
GeneralGood Work Pinmembertonyt8-Dec-08 21:13 
GeneralINotifyPropertyChanging / INotifyPropertyChanged PinmemberMarc Sommer7-Dec-08 8:33 
GeneralRe: INotifyPropertyChanging / INotifyPropertyChanged PinmemberGünther M. FOIDL7-Dec-08 9:48 
GeneralNice PinmemberMaximilian Korporal6-Dec-08 5:14 

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