C#

namespace BallStateExample 
	{
	enum State {Flashing, Played, NotPlayed}
	delegate void BallStateChanged(BallStateChangedEventArgs e);
	
	class BallStateChangedEventArgs
		{
		public int BallIndex { get; set; }
		public State NewState { get; set; }
		}

		
	class Balls
		{
		private readonly State[] _balls;
		
		public Balls(int numBalls)
			{
			_balls = new State[numBalls];
			}
			
		public event BallStateChanged BallStateChanged;

		private void OnBallStateChanged(int index, State newState)
			{
			if (BallStateChanged != null)
				BallStateChanged(new BallStateChangedEventArgs { BallIndex = index, NewState = newState });
			}
			
		public State this[int index]
			{
			get { return _balls[index]; }
			set
				{
				_balls[index] = value;
				OnBallStateChanged(index, value);
				}
			}
		}
		
		
	class BallUser
		{
		private const int NUM_BALLS = 42;
		
		public BallUser()
			{
			Balls = new Balls(NUM_BALLS);
			Balls.BallStateChanged += Balls_StateChanged;
			}
			
		private void Balls_StateChanged(BallStateChangedEventArgs e)
			{
			// Take action in response to a ball state change
			}

		// ...

		// Auto-property (so no backing store need be declared)
		// Private set accessor to prevent consumers of BallUser from
 		// assigning to the property (an action reserved for the constructor of BallUser).
		public Balls Balls { get; private set; }

		// ...
		}
	}

aspdotnetdev wrote:

A new string need not be created each time text is appended to a textbox. As Luc said, you can use AppendText to add to a textbox

aspdotnetdev wrote:

Textbox probably stores the text as an array of strings

aspdotnetdev wrote:

and likely has special getters and setters for the Text property (e.g., if a line was added via AppendText, then add that to the string returned from Text when the getter is called).

Public Overrides Property [Text] As String
    Get
        Return MyBase.Text
    End Get
    Set(ByVal value As String)
        MyBase.Text = value
        Me.selectionSet = False
    End Set
End Property

Public Sub AppendText(ByVal [text] As String)
    If ([text].Length > 0) Then
        Dim num As Integer
        Dim num2 As Integer
        Me.GetSelectionStartAndLength(num, num2)
        Try 
            Dim endPosition As Integer = Me.GetEndPosition
            Me.SelectInternal(endPosition, endPosition, endPosition)
            Me.SelectedText = [text]
        Finally
            If ((MyBase.Width = 0) OrElse (MyBase.Height = 0)) Then
                Me.Select(num, num2)
            End If
        End Try
    End If
End Sub

Luc Pattyn wrote:

how does it avoid concatenation and quadratic behavior

Luc Pattyn wrote:

significantly more text is present than can be seen at any one point in time

Luc Pattyn wrote:

copying all text (or a contiguous block of selected lines) from a ListBox isn't hard at all

aspdotnetdev wrote:

Just didn't like to see people jumping in saying to avoid TextBox like the plague. TextBox has feelings too!

aspdotnetdev wrote:

Also, I don't see any string concatenations in that AppendText function you posted.