Android Example Bidirectional chat with ServerSocket in B4X

I developed a two-way chat system using ServerSocket and Socket in B4X. This project allows a connection to be established between a client and a server within a local network, enabling messages to be exchanged in real time.

Code structure

The system is based on:

- ServerSocket for accepting incoming connections.
- Socket for connecting the client to the server.
- AsyncStreams for handling two-way communication.
- ListView to show available IPs and sent/received messages.

Operation
The server starts listening on the default port (5050).
The client connects to a selected IP via ClientSocket.Connect().
Data is transmitted using AsyncStreams.Write().
Received messages are handled in the AStreamsServer_NewData() and AStreamsClient_NewData()

methods:
GetLocalIP() - Obtains the IP address of the device.
ScanNetwork() - Generates a list of IPs available on the local network.
Ping() - Checks the reachability of a given IP.
SendMessage_Click() - Sends the entered text to the server or client.


If you think this codicie is useful support my efforts here: Donate

'B4XPages

Sub Class_Globals
Private Root As B4XView
    Private xui As XUI
    Private lstIPs As ListView
    Private btnConnect As Button
    Private selectedIP As String
 
    Private xui As XUI
    Private ServerSocket As ServerSocket
    Private ClientSocket As Socket
    Private AStreamsServer As AsyncStreams
    Private AStreamsClient As AsyncStreams
    Private defaultPort As Int = 5050
    Private EditTextIP As EditText
    Private BT_clear_log As Button
    Private SendMessage As Button
End Sub

Public Sub Initialize
'    B4XPages.GetManager.LogEvents = True
End Sub

'This event will be called once, before the page becomes visible.
Private Sub B4XPage_Created (Root1 As B4XView)
    Root = Root1
    Root.LoadLayout("MainPage")
    lstIPs.SingleLineLayout.Label.TextSize = 13
    lstIPs.SingleLineLayout.ItemHeight = 16dip
    Dim myIP As String = GetLocalIP
    lstIPs.AddSingleLine("Indirizzi ip:"&myIP)
    Log("IP Device:"&myIP)
    Sleep(500)
    ' Avvia il server
    ServerSocket.Initialize(defaultPort, "ServerSocket")
    ServerSocket.Listen
    lstIPs.AddSingleLine("VMS server in ascolto... "&myIP)
    Sleep(500)
    lstIPs.AddSingleLine("porta predefinita: "&defaultPort)
    Sleep(500)
 
End Sub

Sub GetLocalIP As String
    Dim Server As ServerSocket
    Server.Initialize(0, "")
    Dim localIP As String = Server.GetMyWifiIP
    Server.Close
    Return localIP
End Sub


'You can see the list of page related events in the B4XPagesManager object. The event name is B4XPage.


Sub lstIPs_ItemClick(Position As Int, Value As Object)
    lstIPs.Clear
 
    selectedIP = Value
    ToastMessageShow("IP selezionato: " & selectedIP, False)
    lstIPs.AddSingleLine("IP Selezionato: "&selectedIP)
    Sleep(500)
    If selectedIP <> "" Then
        ToastMessageShow("Connessione a " & selectedIP, False)
        lstIPs.AddSingleLine("Connessione a:" & selectedIP)
        Sleep(500)
        ' Qui puoi avviare la connessione al server
   
        ' Avvia il server
'ServerSocket.Initialize(defaultPort, "ServerSocket")
    'ServerSocket.Listen
ToastMessageShow("Server in attesa di connessioni...", False)
        lstIPs.AddSingleLine("Server in attesa di connessione...:" )
        Sleep(500)
'        ' Connetti al server remoto (modifica l'IP con quello del dispositivo server)
ClientSocket.Initialize("ClientSocket")
ClientSocket.Connect(selectedIP, defaultPort, 5000) ' Sostituisci con l'
   
    Else
        ToastMessageShow("Seleziona un IP prima di connetterti!", True)
    End If
End Sub

Sub btnConnect_Click
    ScanNetwork
End Sub

' Gestione connessione in entrata (Server)
Sub ServerSocket_NewConnection (Successful As Boolean, NewSocket As Socket)
    If Successful Then
        ToastMessageShow("Connessione stabilita con un client!", False)
        lstIPs.AddSingleLine("Connessione stabilita con client: " & selectedIP)
        Sleep(500)
        AStreamsServer.Initialize(NewSocket.InputStream, NewSocket.OutputStream, "AStreamsServer")
    Else
        ToastMessageShow("Connessione fallita!", True)
        lstIPs.AddSingleLine("Connessione fallita: " & selectedIP)
        Sleep(500)
    End If
End Sub

' Gestione connessione in uscita (Client)
Sub ClientSocket_Connected (Successful As Boolean)
    If Successful Then
        ToastMessageShow("Connesso al server remoto!", False)
        lstIPs.AddSingleLine("Client connesso al server remote: " & selectedIP)
        Sleep(500)
        AStreamsClient.Initialize(ClientSocket.InputStream, ClientSocket.OutputStream, "AStreamsClient")
    Else
        ToastMessageShow("Connessione fallita!", True)
        lstIPs.AddSingleLine("Connessione fallita: " & selectedIP)
        Sleep(500)
    End If
End Sub

' Ricezione dati dal server
Sub AStreamsServer_NewData (Buffer() As Byte)
    Dim msg As String = BytesToString(Buffer, 0, Buffer.Length, "UTF8")
    ToastMessageShow("client: " & msg, False)
    lstIPs.AddSingleLine("client: " & msg)
    Sleep(500)
End Sub
' Ricezione dati dal client
Sub AStreamsClient_NewData (Buffer() As Byte)
    Dim msg As String = BytesToString(Buffer, 0, Buffer.Length, "UTF8")
    'ToastMessageShow("Messaggio ricevuto dal server: " & msg, False)
    lstIPs.AddSingleLine("client: " & msg)
    Sleep(500)
End Sub
' Invio messaggio al server o client
Sub SendMessage_Click
    Dim str As String = EditTextIP.Text
    If AStreamsServer.IsInitialized Then AStreamsServer.Write(str.GetBytes("UTF8"))
    If AStreamsClient.IsInitialized Then AStreamsClient.Write(str.GetBytes("UTF8"))
    ToastMessageShow("Messaggio inviato!", False)
    lstIPs.AddSingleLine("@> "&EditTextIP.Text)
    Sleep(500)
End Sub


Sub ScanNetwork()
    ToastMessageShow("Scansione Avviata...",True)
 
    Dim baseIP As String = "192.168.178."
    Dim activeIPs As List
    activeIPs.Initialize
    Log(activeIPs)
    For i = 1 To 255
        Dim ip As String = baseIP & i
            'If Ping(ip) Then
        activeIPs.Add(ip)
        Log(activeIPs)
        'End If
    Next
    Log(activeIPs)
    lstIPs.Clear
    lstIPs.AddSingleLine("Generazione lista IP")
    For Each ip As String In activeIPs
        lstIPs.AddSingleLine(ip)
    Next
End Sub

Sub Ping(targetIP As String) As Boolean
    Dim p As Phone
    Dim result As Int = p.Shell("ping", Array As String("-c", "178", targetIP), Null, Null)
    Return (result = 0)
End Sub

Sub GetConnectedDevices
    Dim p As Phone
    Dim result As String = p.Shell("ip", Array As String("neigh"), Null, Null)
    Log("Dispositivi connessi: " & result)
    lstIPs.AddSingleLine(result)
End Sub

Private Sub BT_Connetti_Click

    ToastMessageShow("Server in attesa di connessioni...", False)
    lstIPs.AddSingleLine("Server in attesa di connessione... ")
    Sleep(500)
'        ' Connetti al server remoto (modifica l'IP con quello del dispositivo server)
If EditTextIP.Text.Length>0 Then
selectedIP= EditTextIP.Text
    ClientSocket.Initialize("ClientSocket")
    ClientSocket.Connect(selectedIP, defaultPort, 5000) ' Sostituisci con l'
Else
    ToastMessageShow("Inserisci un indirizzo IP e premi 'Connetti'",True)
    End If
 
End Sub

Private Sub BT_clear_log_Click
    lstIPs.Clear
    Dim myIP As String = GetLocalIP
    lstIPs.AddSingleLine("Indirizzo ip:"&myIP&" ~ VMLOG Ver.1.1")
    Sleep(500)
End Sub