Android Question Need Help on Simple Chat b4a example

[ciapw]

Hi. I am really a newbie here. Could you please help me understanding the example? i only knew about c++ so this is really confused me because it's so different.

Sub Process_Globals                                                               //set the variable?
    Type Message (Body As String, From As String)
End Sub

Sub Globals                                                                           //set the variable?
    Private txtHost As EditText
    Private btnConnect As Button
    Private rdbServer As RadioButton
    Private rdbClient As RadioButton
    Private txtName As EditText
End Sub

Sub Activity_Create(FirstTime As Boolean)                                  
    Activity.LoadLayout("1")                                                        //to load the layout
   
    StateManager.RestoreState(Activity, "Main", 0)                       // what is this for?
End Sub

Sub Activity_Pause (UserClosed As Boolean)
    StateManager.SaveState(Activity, "Main")
End Sub


Sub btnConnect_Click
    If txtName.Text = "" Then
        ToastMessageShow("Please enter your name.", True)
        Return
    End If
    If rdbClient.Checked And txtHost.Text = "" Then
        ToastMessageShow("Please enter the server ip address.", True)
        Return
    End If
    Dim host As String = txtHost.Text
    If rdbServer.Checked Then host = "127.0.0.1"
    CallSub3(Starter, "ConnectTo", host, txtName.Text)                 // calling the starter?? does this code link the activity main and starter?
End Sub

Sub Process_Globals
    Private broker As MqttBroker
    Private client As MqttClient
    Private const port As Int = 51042
    Private serializator As B4XSerializator
    Public connected As Boolean
    Private brokerStarted As Boolean
    Private users As List
    Public isServer As Boolean
    Private currentName As String
End Sub

Sub Service_Create
    broker.Initialize("", port)                        //to set up the broker? i dont want to use my phone as broker so should i omit this?
    broker.DebugLog = False
    users.Initialize
End Sub

Sub Service_Start (StartingIntent As Intent)

End Sub

Public Sub ConnectTo(Host As String, Name As String)                  //connecting the phone to host?
    currentName = Name
    isServer = Host = "127.0.0.1"
    If isServer Then
        If brokerStarted = False Then
            broker.Start
            brokerStarted = True
        End If
        users.Clear
        Host = "127.0.0.1"
    End If
    If connected Then client.Close
    client.Initialize("client", $"tcp://${Host}:${port}"$, "android" & Rnd(1, 10000000))
    Dim mo As MqttConnectOptions
    mo.Initialize("", "")
    'this message will be sent if the client is disconnected unexpectedly.
    mo.SetLastWill("all/disconnect", serializator.ConvertObjectToBytes(currentName), 0, False)
    client.Connect2(mo)
End Sub

Private Sub client_Connected (Success As Boolean)
    Log($"Connected: ${Success}"$)
    If Success Then
        connected = True
        client.Subscribe("all/#", 0)
        client.Publish2("all/connect", serializator.ConvertObjectToBytes(currentName), 0, False)
    Else
        ToastMessageShow("Error connecting: " & LastException, True)
    End If
End Sub

Private Sub client_MessageArrived (Topic As String, Payload() As Byte)
    Dim receivedObject As Object = serializator.ConvertBytesToObject(Payload)
    If Topic = "all/connect" Or Topic = "all/disconnect" Then
        'new client has connected or disconnected
        Dim newUser As String = receivedObject
        If isServer Then
            Log($"${Topic}: ${newUser}"$)
            Dim index As Int = users.IndexOf(newUser)
            If Topic.EndsWith("connect") And index = -1 Then users.Add(newUser)
            If Topic.EndsWith("disconnect") And index >= 0 Then users.RemoveAt(index)
            client.Publish2("all/users", serializator.ConvertObjectToBytes(users), 0, False)
        End If
    Else if Topic = "all/users" Then
        Dim newUsers As List = receivedObject
        CallSubDelayed2(Chat, "NewUsers", newUsers) 'this will start the chat activity if it wasn't started yet.
    Else
        Dim m As Message = receivedObject
        CallSub2(Chat, "NewMessage", m)
    End If
       
End Sub

Public Sub SendMessage(Body As String)
    If connected Then
        client.Publish2("all", CreateMessage(Body), 0, False)
    End If
End Sub

Public Sub Disconnect
    If connected Then client.Close
End Sub

Private Sub CreateMessage(Body As String) As Byte()
    Dim m As Message
    m.Initialize
    m.Body = Body
    m.From = currentName
    Return serializator.ConvertObjectToBytes(m)
End Sub

Private Sub client_Disconnected
    connected = False
    If IsPaused(Chat) = False Then
        CallSub(Chat, "Disconnected")
    End If
    If isServer Then
        broker.Stop
        brokerStarted = False
    End If
End Sub


Sub Application_Error (Error As Exception, StackTrace As String) As Boolean
    Return True
End Sub

Sub Service_Destroy

End Sub

the point is? in c++ u call all your needed procedure in main() but in b4a we can't do it like that? did all the sub will be executed in order?

 

[Erel]

See my answer in the chat example thread. Start with learning the B4A and B4J solutions.