Visual Basic.NET How to Program (PDF)

1116 Networking: Streams-Based Sockets and Datagrams Chapter 22
time, even while a packet is being received. The event handler for the TextBox processes
the event and sends the data to the server.
22.6 Client/Server Tic-Tac-Toe Using a Multithreaded Server
In this section, we present our capstone networking example—the popular game Tic-Tac-
Toe, implemented with stream sockets and client/server techniques. The program consists
of a FrmServer application (Fig. 22.5) and two FrmClient applications (Fig. 22.7);
FrmServer allows the FrmClients to connect to the server and play Tic-Tac-Toe. We
depict the output in Fig. 22.7. When the server receives a client connection, lines 67–78 of
Fig. 22.5 create an instance of class CPlayer to process the client in a separate thread of
execution. This enables the server to handle requests from both clients. The server assigns
value "X" to the first client that connects (player X makes the first move), then assigns value
"O" to the second client. Throughout the game, the server maintains information regarding
the status of the board so that the server can validate players’ requested moves.
However, neither the server nor the client can establish whether a player has won the
game—in this application, method GameOver (lines 166–170) always returns False.
Exercise 22.7 asks the reader to implement functionality that enables the application to determine
a winner. Each FrmClient maintains its own GUI version of the Tic-Tac-Toe
board to display the game. The clients can place marks only in empty squares on the board.
Class CSquare (Fig. 22.8) is used to define squares on the Tic-Tac-Toe board.
1 ' Fig. 22.5: Server.vb
2 ' Server maintains a Tic-Tac-Toe game for two client applications.
3
4 Imports System.Windows.Forms
5 Imports System.Net.Sockets
6 Imports System.Threading
7
8 Public Class FrmServer
9 Inherits Form
10
11 ' TextBox for displaying results
12 Friend WithEvents txtDisplay As TextBox
13
14 Private board As Char() ' Tic-Tac-Toe game board
15
16 Private players As CPlayer() ' player-client applications
17 Private playerThreads As Thread() ' Threads that run clients
18
19 ' indicates current player ("X" or "O")
20 Private currentPlayer As Integer
21
22 ' indicates whether server has disconnected
23 Private disconnect As Boolean = False
24
25 Public Sub New()
26 MyBase.New()
27
Fig. 22.5 Server side of client/server Tic-Tac-Toe program (part 1 of 4).