Take Your Apps Far and Wide with a GPS Tracking System  : Page 4

Modifying the Pocket PC Application
Back in the Pocket PC (GPSTracking) project, add a new Class item to the project and name it as Sync.vb. Populate the class with the following:

Imports System.Net
Imports System.Net.Sockets

Public Class Sync
    Const portNo As Integer = 3456
    Dim client As Socket

    Public Sub PerformSync( _
       ByVal HostIP As String, _
       ByVal txtData As String)
        Try
            Dim RemoteAdd As System.Net.IPAddress = _
               System.Net.IPAddress.Parse(HostIP)
            Dim endPoint As New IPEndPoint(RemoteAdd, portNo)
            client = New Socket(endPoint.AddressFamily, _
                     SocketType.Stream, ProtocolType.Tcp)
            client.Connect(endPoint)

            '---send a message to the server
            Dim data As Byte() = _
            System.Text.Encoding.ASCII.GetBytes(txtData)

            '---send the text---
            client.Send(data)
            client.Close()
        Catch ex As Exception
            MsgBox(ex.ToString)
        End Try
    End Sub
End Class

The purpose of this class is to open a socket connection to the server and send the ID of the user, as well as latitude and longitude information, to it.

In Form1.vb, declare and instantiate the Sync class so that you can connect to the server:

Figure 9. Testing the entire system and tracking two different users.

Public Class Form1
    '---use for synchronization---
    Dim sync As New Sync

Modify the processGPSData() subroutine so that after displaying the latitude and longitude information on the screen, you will send the data to the server:

    Private Sub processGPSData(ByVal str As String)
        Dim rawLatLng As Double
        Try
        ...
        ...
                    '---display the lat and lng---
                    lblLat.Text = "Lat:" & lat
                    lblLng.Text = "Lng:" & lng

                    '---synchronize with the server---
                    sync.PerformSync(ServerIP, ID & ":" & lat & ":" & 
        ...
        ...
    End Sub

That's it! You can now test the entire system. With the server running, run the Pocket PC application and click the Connect GPS menu item. By default, the ID of the Pocket PC application is set to "1", and hence the left map on the server (see Figure 9) will display the location for user "1". If you set the ID of the Pocket PC application to "2", the right map will be updated instead. Hence, the system in this article allows two Pocket PCs to be traced at the same time (of course, you can scale it up to monitor multiple users).

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