Connected Mobile and Web Applications with

AngeloCorsaro,PhDChiefTechnologyOfficer

angelo.corsaro@prismtech.com

Connectivity

IaaS

analytics

operational systems

information systems

mobile

desktop

web

embeddedfog computing

integration

Vortex “Connectivity” Model

Applications can autonomously and asynchronously read and write data enjoying spatial and

temporal decoupling DDS Global Data Space

...

Data Writer

Data Writer

Data Writer

Data Reader

Data Reader

Data Reader

Data Reader

Data Writer

TopicAQoS

TopicBQoS

TopicCQoS

TopicDQoS

Global Data Space

Built-in dynamic discovery isolates applications from

network topology and connectivity details

DDS Global Data Space

...

Data Writer

Data Writer

Data Writer

Data Reader

Data Reader

Data Reader

Data Reader

Data Writer

TopicAQoS

TopicBQoS

TopicCQoS

TopicDQoS

Dynamic Discovery

QoS policies allow to express temporal and availability

constraints for data

DDS Global Data Space

...

Data Writer

Data Writer

Data Writer

Data Reader

Data Reader

Data Reader

Data Reader

Data Writer

TopicAQoS

TopicBQoS

TopicCQoS

TopicDQoS

QoS - Enabled

No single point of failure or bottleneck

Decentralised Data Space Data

Writer

Data Writer

Data Writer

Data Reader

Data Reader

Data Reader

Data Writer

TopicAQoS

TopicBQoS

TopicCQoS

TopicDQoS

TopicDQoS

TopicDQoS

TopicAQoS

Connectivity is dynamically adapted to chose the most

effective way of sharing data

Adaptive ConnectivityData

Writer

Data Writer

Data Writer

Data Reader

Data Reader

Data Reader

Data Writer

TopicAQoS

TopicBQoS

TopicCQoS

TopicDQoS

TopicDQoS

TopicDQoS

TopicAQoS

ThecommunicationbetweentheDataWriterandmatchingDataReaderscanbepeer-to-peerexploitingUDP/IP(UnicastandMulticast)orTCP/IP

ThecommunicationbetweentheDataWriterandmatchingDataReaderscanbe“brokered”butstillexploitingUDP/IP(UnicastandMulticast)orTCP/IP

A domain-wide information’s class A Topic defined by means

of a <name, type, qos>

TopicDDS Global Data Space

...

Data Writer

Data Writer

Data Writer

Data Reader

Data Reader

Data Reader

Data Reader

Data Writer

TopicAQoS

TopicBQoS

TopicCQoS

TopicDQoS

TopicTypeName

QoS

Topic types can be expressed using different syntaxes,

including IDL and ProtoBuf

Topic Type struct CarDynamics { string cid; long x; long y; float dx; long dy; } #pragma keylist CarDynamics cid

IDL

Topic types can be expressed using different syntaxes,

including IDL and ProtoBuf

Topic Type message CarDynamics { option (.omg.dds.type) = {name: "CarDynamics"}; required string cid = 0 [(.omg.dds.member).key = true]; required long x = 1; required long y = 2; required float dx = 3; required long dy = 4; }

ProtoBuf

Topic types can be expressed using different syntaxes,

including IDL and ProtoBuf

Topic Type class CarDynamics: constructor: (@cid, @x, @y, @dx, @dy) ->

CoffeeScript

Topic types can be expressed using different syntaxes,

including IDL and ProtoBuf

Topic Type public struct VehicleDynamics { public string cid { get; set; } public int x { get; set; } public int y { get; set; } public int dx { get; set; } public int dy { get; set; } public VehicleDynamics (string cid, int x, int y, int dx, int dy) { this.cid = cid; this.x = x; this.y = y; this.dx = dx; this.dy = dy; } }

C#

Vortex “knows” about application

data types and uses this

information provide type-

safety and content-based

routing

Content Awareness structCarDynamics{

@keystringcid;longx;longy;floatdx;longdy;}

cid x y dx dyGR 33N GO 167 240 45 0LO 00V IN 65 26 65 0AN 637 OS 32 853 0 50AB 123 CD 325 235 80 0

“dx>50ORdy>50”

Type

CarDynamics

cid x y dx dyLO 00V IN 65 26 65 0AB 123 CD 325 235 80 0

A collection of policies that control non-functional

properties such as reliability, persistence, temporal

constraints and priority

QoS HISTORY

LIFESPAN

DURABILITY

DEADLINE

LATENCY BUDGET

TRANSPORT PRIO

TIME-BASED FILTER

RESOURCE LIMITS

USER DATA

TOPIC DATA

GROUP DATA

OWENERSHIP

OWN. STRENGTH

LIVELINESS

ENTITY FACTORY

DW LIFECYCLE

DR LIFECYCLE

PRESENTATION

RELIABILITY

PARTITION

DEST. ORDER

RxO QoS Local QoS

QoS Policies controlling end-to-end properties follow a Request

vs. Offered

QoS Domain

Participant

DURABILITY

OWENERSHIP

DEADLINE

LATENCY BUDGET

LIVELINESS

RELIABILITY

DEST. ORDER

Publisher

DataWriter

PARTITION

DataReader

Subscriber

DomainParticipant

offered QoS

Topicwrites reads

Domain Idjoins joins

produces-in consumes-from

RxO QoS Policies

requested QoS

Vortex Technology Stack

Device-2-DeviceDevice-2-Cloud

Fog-2-Cloud

Device-2-Fog

Cloud-2-Cloud

Fog-2-Fog

Device implementations optimised for OT, IT and

consumer platforms

Native support for Cloud and Fog Computing Architectures

Available across IT, Consumer and OT platforms Device-2-DeviceDevice-2-Cloud

Fog-2-Cloud

Device-2-Fog

Cloud-2-Cloud

Fog-2-Fog

Polyglot and Interoperable across Programming

Languages Device-2-DeviceDevice-2-Cloud

Fog-2-Cloud

Device-2-Fog

Cloud-2-Cloud

Fog-2-Fog

Fully Independent of the Cloud Infrastructure

Device-2-DeviceDevice-2-Cloud

Fog-2-Cloud

Device-2-Fog

Cloud-2-Cloud

Fog-2-Fog

Private Clouds

Native Integration with the hottest real-time analytics

platforms and CEP Device-2-DeviceDevice-2-Cloud

Fog-2-Cloud

Device-2-Fog

Cloud-2-Cloud

Fog-2-Fog

Device-2-DeviceDevice-2-Cloud

Fog-2-Cloud

Device-2-Fog

Cloud-2-Cloud

Fog-2-Fog

High Performance

30 μs peer-to-peer latency

4.2M+ msgs/sec peer-to-peer throughput

Device-2-DeviceDevice-2-Cloud

Fog-2-Cloud

Device-2-Fog

Cloud-2-Cloud

Fog-2-Fog

High Performance

4 μs fog/cloud routing latency

Device-2-DeviceDevice-2-Cloud

Fog-2-Cloud

Device-2-Fog

Cloud-2-Cloud

Fog-2-Fog

SecureData-Level security with

Pluggable Authentication Access Control and Crypto

Real-World Example

Vortex device such are used to share data between different kinds of applications within a car

Café can be used in Android based infotainment

Lite in ECU, sensors and onboard analytics

Vortex Fog is used to transparently (for in car apps) decouple and control the data sharing within and across the car

Vortex Fog also helps defining security boundaries and policies

Vortex Fog efficiently and securely deals with car to car communication

Vortex Fog efficiently and securely deals with cloud connectivity adapting traffic flows and protocols

Device-to-Cloud Communication

Cloud Analytics

Fog AnalyticsFog Analytics

Fog Analytics

Vortex Cloud efficiently and securely makes data available to any device at an Internet Scale

Device-to-Cloud Communication

Cloud Analytics

Fog AnalyticsFog Analytics

Fog Analytics

Web and Mobile in Vortex

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• A JavaScript DDS API to provide HTML5/JavaScript applications with a high-level communication abstraction

• Vortex Web exploits HTML5 features, such as web-sockets and web-workers, to provide time and space efficient Web-App to Cloud communication

Vortex Web

DDS#API JavaScript

Browser#/#Node.js

CoffeeScript

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Client Side (dds.js): JavaScript CoffeeScript and .NET API for accessing DDS abstractions

Server Side (vortex-web): A Router that transparently bridges data between matching DDS entities, e.g. Browser-2-Browser, DDS-2-Browser and Browser-2-DDS

Vortex Web

TopicA

TopicB

TopicC

TopicDQoS

QoS

QoS

QoSData

Reader

Data Reader

Data Writer

Data Writer

dds.js

dds.js

v-web

v-web

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4Vortex-Web takes advantage of HTML5 WebSockets as well as Web Workers

WebSockets are used for both the control as well as the data plane

Web Workers are used to decouple I/O from processing (recall that a JS context is single-threaded)

Client-Side Architecture / JS

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JS-Client ArchitectureControl-Link.js

Send-Link.js

Recv-Link.js

dds-runtime.jsdds.js

mainworker(orwindowcontext)

worker

worker

worker

worker

Vortex-WebServer

control-protocol

data(frombrowser)

data(

tobro

wser)

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The .NET client for Vortex-Web takes advantage of the async / await support for providing a lightweight, scalable and efficient client API.

Independent WebSockets are used for both the control and the data plane

Client-Side Architecture / .NET

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.Net Client Architecture

vortex.web.sharp

Vortex-WebServer

control-protocol

data(frombrowser)

data(tobrowser)

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Vortex-Web can be deployed to simply provide access to a “regular” DDS system or to extend Vortex-Cloud with JavaScript / pure .Net support

In general, you should think of Vortex-Web as an add-on to either a regular or a Vortex-Cloud DDS system

Vortex-Web takes advantage of DDS to support fault-tolerance and load-balancing

Vortex Web Deployment

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Multiple instances can be deployed on a single system to provide fault-tolerance as well as to help in partitioning the load

The switch-over between instances is dealt-with by the client library

Traditional System Deployment

TopicA

TopicB

TopicC

TopicDQoS

QoS

QoS

QoSData

Reader

Data Reader

Data Writer

Data Writer

dds.js

dds.js

v-web

v-web

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Multiple instances can be deployed on the same IaaS platform sa Vortex-Cloud provide fault-tolerance as well as to help in partitioning the front-end load

The switch-over between instances is dealt-with by the dds.js library

Cloud Based Deployment

VORTEXCloud

IaaSserver-side

dds.jsdds.js

dds.js Overview

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Runtime

runtime = new dds.runtime.Runtime();runtime.connect(server, authToken);

CoffeeScript

Example:

runtime = new dds.runtime.Runtime()runtime.connect(“ws://88.77.66.55:9876”, “albator:corsaire”);

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Topic

cell = new dds.Topic(0, 'Cell', ‘com.activefloor.Cell')runtime.registerTopic(cell)

post = new dds.Topic(0, 'Post')runtime.registerTopic(post)

myTopic = new dds.Topic(domainID, topicName, topicType)runtime.registerTopic(myTopic)

CoffeeScript

Example:

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DataWriter

dw = new dds.DataWriter(runtime, topic, qos)

post = {}post.name = “kydos”post.msg = “having fun with Vortex Web”

dw.write(post)

dw = new dds.DataWriter(runtime, topic, qos)

CoffeeScript

Example:

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DataReader

dr = new dds.DataReader(runtime, topic, qos)

dr = new dds.DataReader(runtime, topic, qos)

CoffeeScript

Example:

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A DataReader can be bound to a user provided function that will handle incoming data or to a cache

Notice, that as you are in control of how data-readers are bound to cache you can be very creative

Binding a DataReader

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Binding to User Function

dr.addListener((s) -> console.log(JSON.stringify(s)))

dr.addListener(f)CoffeeScript

Example:

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Binding to a Cache

// BindingbindCell = dds.bind((s) -> s.x + “-” + s.y)ccache = new DataCache(historyDepth)bindCell(ccache, cdr)

// Working with the Cache: Compute number of active cellsactiveCells = ccache.map((c) -> if (c.pressure > p0) then 1 else 0).fold(0)((a, c) -> a + c)

cache = new DataCache(historyDepth)bind(keyMapper)(dr, cache)

CoffeeScript

Example:

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DataCache Operations

# Writes a data sample into the cache corresponding to the key k write: (k, data)

# Returns a list representing the content of the cache ordered by key.read()

# Returns a list representing the last sample for each keyreadLast()

# Returns a list representing the content of the cache ordered by key. # The data is actually removed from the cache.take()

# Returns a list representing the last sample for each key# The data is actually removed from the cache.takeLast()

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DataCache Operations

# Returns a list representing the content of the cache that matches for given predicate.# The data is actually removed from the cache.takeWithFilter(p)

# Returns Some(v) if a value associated to the key k exists. Otherwise it returns Noneget: (k)

# Returns Some(v) if a value associated to the key k exists. Otherwise it returns f()getOrElse(k, f)

# Clear the content of the cache.clear()

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DataCache Operations

# Returns a new DataCache whose content is obtained by applying the function# f to each element of the cachemap(f)

# Executes the function f on each element of the cacheforEach(f)

# Executes the function f only on the first n samples associated with a keyforEachN(f, n) # Returns the element of the cache that match the predicate pfilter(p)

# Returns the element of the cache that do not match the predicate pfilterNot(p)

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DataCache Operations

# Folds the content of the data cache using z as “zero” for the folding function f# For instance, assuming that the operator “+” is defined for the elements of # the cache, then you could compute the sum of all elements doing:# c.fold(0)((a, v) -> a + v)# the product by: # c.fold(1)((a, v) -> a * v)# a comma separated string representation of the content:# c.fold(“”)(a, v) -> a + “, “ + vfold(z)(f)

# Register a listener l to be notified whenever data which matches a # predicate p is written into the cache. If no predicate is provided # then the listeners is always notified upon data insertion.addListener(l, p)

hacking time

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4Let’s see the steps required to build a Web Chat that may look like this

But before let’s play with it a bit

Web Chat

http://demo.prismtech.com

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The Chat CoffeeScript#CreateusefulaliasforcoffezandjQueryroot=thisz_=coffez$=jQuery

server=“ws://demo-eu.prismtech.com:9999"

#TheposttypeusedbythechatapplicationclassPostconstructor:(@name,@msg)->

#Createtheruntimeruntime=newdds.runtime.Runtime()

#DefinethePosttopicusedtosendandreceivechatpostspostTopic=newdds.Topic(0,"Post")

#DefinetheQoSfortheDataReader/WriterdrQos=newdds.DataReaderQos(dds.Reliability.Reliable)dwQos=newdds.DataWriterQos(dds.Reliability.Reliable)

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The Chat CoffeeScriptpostReader=z_.NonepostWriter=z_.None

avatar="avatar"+Math.floor((Math.random()*10000)+1);

#AddposttothechatandformatittoshowitisfrommecreateMyPost=(post)->...

#AddposttothechatandformatittoshowitisfromotherscreateOtherPost=(post)->...

#AddposttothechatandformatittoshowitisfromothersprocessPost=()->msg=$("#ChatMessage").val()post=newPost(avatar,msg)#Publishthepost(noticethatpostWriterisanOptionMonad)#Takealookat(http://en.wikibooks.org/wiki/Haskell/Understanding_monads/Maybe)#or(http://www.scala-lang.org/api/2.11.0/index.html#scala.Option)postWriter.map((dw)->dw.write(post))$("#ChatMessageList").append(createMyPost(post))$("#ChatMessage").val("")

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The Chat CoffeeScript#Dealwithclickandkeysevents…

$("#ChatMessage").keyup((e)->if(e.keyCodeis13)thenprocessPost())

$("#SendMsgButton").click((evt)->console.log("SendButtonhasbeenclicked")processPost())

$("#SelectAvatarButton").click((evt)->s=$("#AvatarName").val()if(sisnt"")avatar=s)

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The Chat CoffeeScript#Handletheruntimeonconnecteventruntime.onconnect=()->#CreateDataReaderandDataWriterforourposts

runtime.registerTopic(postTopic)dr=newdds.DataReader(runtime,postTopic,drQos)dw=newdds.DataWriter(runtime,postTopic,dwQos)

#Registeralistenerwiththedatareadertopostmessages#inourchatdr.addListener((post)->if(post.nameisntavatar)$("#ChatMessageList").append(createOtherPost(post)))postReader=z_.Some(dr)postWriter=z_.Some(dw)

connectRuntime=()->$("#AvatarName").val(avatar)runtime.connect(server,"uid:pwd")

$(document).ready(()->connectRuntime())

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4Only ~10 lines code for implementing the communication required by a chat application!

Content filtering could be used to further simplify the application and reduce number of lines of code, i.e. avoid the check on the origin of the message to avoid duplicate posts

In Summary

some hacking. . .

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Very close to the JavaScript/CoffeScript API

Takes advantage of async /await

Pure .Net API without any native dependencies.

Latest Nuget Package available at

- https://www.nuget.org/packages/vortex.web.sharp/0.1.3-alpha

.NET API for Vortex Web

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4C# implementation of a Chat with a minimalistic GUI

GUI coded in GTKSharp

The same business logic could be targeted to Android / iOS using Xamarin Studio

.Net SharpChat

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Topic Types are defined in C#

The Post Type

public class Post { public string name { get; } public string msg { get; } public Post (string name, string msg) { this.name = name; this.msg = msg; } }

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.Net SharpChat

class MainClass { public static void Main (string[] args) { var user = args.Length > 0 ? args [0] : “anonymous”; var uri = args.Length > 1 ? args [1] : ”ws://localhost:9000”; var vortex = new VortexApp (user, uri); vortex.Run (); } }

class VortexApp { public DataWriter<Post> dw { get; set; } public DataReader<Post> dr { get; set; } private MainWindow win; public string user { get; } public string uri { get; } public VortexApp(string user, string uri) { this.user = user; this.uri = uri; } public async Task Init() { var auth = user + ":nopwd"; var v = new Vortex (0); await v.Connect (uri, auth); if (v.IsConnected) { var tname = "Post"; var post = await v.CreateTopic<Post> (tname); dr = await v.CreateDataReader<Post> (post); dw = await v.CreateDataWriter<Post> (post); } else Console.WriteLine ("Unable to connect to: " + uri); } public void Run () { Application.Init (); Init ().Wait (); win = new MainWindow (user, this.dw); win.Show (); dr.OnDataAvailable += (object sender, SampleData<Post> e) => { win.addPost(e.Data); } ; Application.Run (); } }

Listener are lambdas

Readers and Writers are strongly typed (but can do projections)

using System;using Gtk;using vortex.web;using sharpchat;public partial class MainWindow: Gtk.Window{ private DataWriter<Post> dw; private string user; […]

protected void onKeyReleaseEvent (object o, KeyReleaseEventArgs args) { var k = args.Event.Key; if (k == Gdk.Key.Return) { var rmsg = this.inputText.Buffer.Text; var msg = rmsg.Remove(rmsg.Length -1); dw.Write(new Post(this.user, msg)); this.inputText.Buffer.Clear (); } } private void appendToMessageBoard (string user, string msg) { var text = this.messageBoard.Buffer.Text + "\ n" + user + " >> " + msg; this.messageBoard.Buffer.Text = text; } public void addPost(Post p) { appendToMessageBoard (p.name, p.msg); } }

Async Write

Dashboards

Vortex integrates with Freeboard and makes it supersimple to create dashboards from data coming from Mobile, Web, Embedded, and Cloud apps

Native Mobile Apps

Vortex Cafe can be used to develop android applications in Java

The .Net client for Vortex-Web can be used to along with Xamain to develop native applications for Android , iOS and Windows Phone

The JS client for Vortex-Web can be used to develop native applications with Apache Cordova.

Vortex Cafe

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Pure Java version of Vortex targeting JVM and embedded JVMs

DDSI Protocol Stack optimised for mobility and Android OS

Only DDS on the market designed and Engineered for Android

Vortex Café

J2SE

DDSI$$(Optimised*for*Mobility)*

DDS$API Java Scala JavaScript

Android Chat

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4To learn how to write an Android Application that uses Vortex Café we’ll develop a very simple Chat

To keep things simple this chat will have a single “chat room”

DDS Chat for Android

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Our Chat application will have a very simple architecture with simply one Activity that will take care of:

- Sending Posts into the ChatRoom

- Displaying Posts in the room since when we joined

In terms of information modelling, we’ll have a single topic representing the user post

Step 1: Architecture

structPost{stringname;stringmsg;};#pragmakeylistPostname

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Creating DDS entities, such as DomainParticipants, DataReaders and DataWriters involves network communication, such as discovery information

In addition when an a DDS entity is destroyed it looses its state

As such, tying the life-cycle of DDS entities to activities should be done with great care

Step 2: Lifecycle Management[1/2]

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In general, it is a better idea to tie the life-cycle of DDS entities to the Application as opposed to Activities

In some cases, it may make sense to tie the life-cycle of DataReaders/DataWriters to that of the activity that relies on them -- Usually this makes sense for activities that are “one-off”

Step 2: Lifecycle Management[2/2]

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Applicationpublic class ChatApplication extends Application {

DataReader<Post> dr; DataWriter <Post> dw; DomainParticipant dp;

@Override public void onCreate() { super.onCreate(); // This should be defined via a resource -- but for a small // demo that’s OK.

System.setProperty(ServiceEnvironment.IMPLEMENTATION_CLASS_NAME_PROPERTY, "com.prismtech.cafe.core.ServiceEnvironmentImpl"); ServiceEnvironment env = ServiceEnvironment.createInstance( ChatApplication.class.getClassLoader()); DomainParticipantFactory dpf = DomainParticipantFactory.getInstance(env);

dp = dpf.createParticipant(0); Topic<Post> topic = dp.createTopic("Post",Post.class); Publisher pub = dp.createPublisher(); Subscriber sub = dp.createSubscriber();

dw = pub.createDataWriter(topic); dr = sub.createDataReader(topic); }

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Application

public DataReader<Post> reader() { return this.dr; }

public DataWriter<Post> writer() { return this.dw; }

@Override public void onTerminate() { super.onTerminate(); this.dp.close(); }}

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Manifest...

<application android:allowBackup="true" android:icon="@drawable/ic_launcher" android:label="@string/app_name" android:theme="@style/AppTheme" android:name="ChatApplication" > <activity android:name=“com.ddschat.MainActivity" android:label="@string/app_name" > <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity></application>

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When using Vortex Café you need to grant the proper permissions for networking:

More Manifest...

<uses-permission android:name="android.permission.INTERNET"/><uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/><uses-permission android:name="android.permission.CHANGE_WIFI_MULTICAST_STATE"/>

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Activity GUI<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" >

<TextView android:id="@+id/chatMessages" android:layout_width="match_parent" android:layout_height="wrap_content" android:text="@string/chat_msgs" android:visibility="gone" android:background="#666" android:textColor="#fff" android:paddingLeft="5dp" /> <ListView android:id="@+id/messageList" android:layout_width="match_parent" android:layout_height="0dp" android:layout_weight="1" />

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Activity GUI

<LinearLayout android:layout_width="fill_parent" android:layout_height="wrap_content" android:orientation="horizontal" >

<EditText android:id="@+id/message" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_weight="1" android:hint="@string/edit_message" />

<Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:onClick="sendChatMessage" android:text="@string/button_send" /> </LinearLayout>

</LinearLayout>

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Activity 1 2 public class MainActivity extends Activity { 3 4 private static final String TAG = "ChatMainActivity"; 5 private final Handler handler = new Handler(); 6 private ArrayAdapter<String> chatMessages; 7 8 public class ChatMessageListener extends ChatMessageDataListener { 9 // ...10 }11 12 @Override13 protected void onCreate(Bundle savedInstanceState) {14 super.onCreate(savedInstanceState);15 setContentView(R.layout.activity_main);16 chatMessages = new ArrayAdapter<String>(this, R.layout.messages);17 chatMessages.add("Welcome to the DDS Chat Room");18 ListView mview = (ListView) findViewById(R.id.messageList);19 mview.setAdapter(chatMessages);20 ChatApplication app = (ChatApplication) getApplication();21 22 app.reader().setListener(new ChatMessageListener());23 24 }25

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Activity

25 26 @Override27 public boolean onCreateOptionsMenu(Menu menu) {28 // Inflate the menu; this adds items to the action bar if it is present.29 getMenuInflater().inflate(R.menu.main, menu);30 return true;31 }

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Activity

32 33 public void sendChatMessage(View view) {34 EditText editText = (EditText) findViewById(R.id.message);35 String msg = editText.getText().toString();36 editText.setText("");37 // chatMessages.add(msg);38 ChatApplication app = (ChatApplication) getApplication();39 try {40 Log.i(TAG, ">>> Sending data " + msg);41 app.writer().write(new Post(usr, msg));42 } catch (TimeoutException te) {43 }44 }45 46 }

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Receiving data is a bit trickier since in Android only the thread that runs an activity has the right to change the UI

This means, that from a DDS listener it is not possible to change an the UI directly!

The solution is to use an Android Handlerto which we can post Runnable to be executed by the activity thread

Let’s see how this works...

Receiving Data

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DDS Listener & Android Handler

1 public class ChatMessageListener extends ChatMessageDataListener { 2 3 private DataReader<Post> dr; 4 5 public ChatMessageListener() { 6 ChatApplication app = (ChatApplication) getApplication(); 7 dr = app.reader(); 8 } 9

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DDS Listener & Android Handler10 @Override11 public void onDataAvailable(DataAvailableEvent<Post> dae) {12 final Iterator<Post> i = dr.read();13 14 Log.i(TAG, ">>> DataReaderListener.onDataAvailable");15 if (i.hasNext()) {16 Runnable dispatcher = new Runnable() {17 public void run() {18 while (i.hasNext()) {19 Sample<Post> s = i.next();20 21 if (s.getSampleState() == SampleState.NOT_READ) {22 Post cm = s.getData();23 chatMessages.add(cm.name + " > " + cm.msg);24 }25 }26 }27 };28 handler.post(dispatcher);29 }30 }31 }

Live Demo

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