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Revision as of 05:02, 12 March 2008 by Grundleborg (talk | contribs) (class implementation code and start explanation)

Development/Tutorials/Decibel/Handling TextChannels


This tutorial will walk you through the process of creating a simple application that uses Decibel's TextChannels to communicate via arbitrary instant messaging networks using telepathy. From the result of this tutorial, only a few more lines of code are needed to produce a functioning text based instant messaging client.

This tutorial is based on the simpleclient demo included with Decibel. An explanation of using the simpleclient demo can be found here.

In this tutorial, we only pick out the important parts of the source code to discuss. The complete working source code for this example can be found here in KDE's SVN Repository.

ChannelHandler class

The first class we will need to create is an implementation of the Decibel::ChannelHandler interface.

The Class Definition

Here is the class definition for our implementation of the Decibel::ChannelHandler interface. It is explained below.

class MyTextChannelHandler : public Decibel::ChannelHandler {



   explicit MyTextChannelHandler(QObject * parent = 0);
   bool handleChannel(QtTapioca::Connection *, QtTapioca::Channel *, const bool);

public slots:

   void onMessageReceived();
   void onCloseChannel();


   QtTapioca::Connection *  m_connection;
   QtTapioca::TextChannel * m_channel;


We must inherit from Decibel::ChannelHandler which is the interface definition for handling incoming Channels. We reimplement the constructor, Destructor and the handleChannel() method as well as adding two slots of our own. We also create the member variables m_connecion and m_channel which will hold the QtTapioca::Connection and QtTapioca::Channel objects that are received by the handleChannel method.

The Class Implementation

Now that we have defined our Decibel::ChannelHandler subclass, we need to implement its methods.

MyTextChannelHandler::MyTextChannelHandler(QObject * parent) :


{ } The constructor is very simple. We just pass the parent object on to the parent class and initialise our member variables to 0.

MyTextChannelHandler::~MyTextChannelHandler() { } The destructor is even simpler. We don't need to do anything in it because Qt will handle the deletion of child objects automatically.

bool MyTextChannelHandler::handleChannel(QtTapioca::Connection * connection,

                                        QtTapioca::Channel * channel,
                                        const bool)


   Q_ASSERT(connection != 0);
   Q_ASSERT(channel != 0);
   if (m_connection != 0) { return false; }
   m_channel = dynamic_cast<QtTapioca::TextChannel*>(channel);
   if (m_channel == 0)
       return false;
   m_connection = connection;
   connect(m_channel, SIGNAL(messageReceived(const QtTapioca::TextChannel *, const QtTapioca::TextChannel::Message &)),
           this, SLOT(onMessageReceived()));
   connect(m_channel, SIGNAL(closed()), this, SLOT(onCloseChannel()));
   return true;


void MyTextChannelHandler::onCloseChannel() {

   m_connection = 0;
   m_channel = 0;


void MyTextChannelHandler::onMessageReceived() {

   QList<QtTapioca::TextChannel::Message> message_list = m_channel->pendingMessages();
   for (QList<QtTapioca::TextChannel::Message>::const_iterator
            message = message_list.constBegin();
        message != message_list.constEnd(); ++message)
       if (message->type() == QtTapioca::TextChannel::Message::Normal &&
           message->contents() == QString("ping?"))
       { m_channel->sendMessage(QString("pong!")); }


This page was last edited on 16 May 2019, at 11:04. Content is available under Creative Commons License SA 4.0 unless otherwise noted.