Programming Jabber

What the Headline Viewer Is Going to Do

The headline viewer, shown in Figure 9-10, has a scrollable area where headlines are displayed. We can clear that area, or select a headline and call up a web browser to fetch the story by passing the URL to it.

Figure 9-10. The Headline Viewer client

It’s also nice and small, visually and in the amount of code we’re going to have to write. We connect to the Jabber server, set up a handler for the incoming headline messages, build the display, send our availability, and sit back and watch the news roll in.

Actually, we need to say a few things about the “sitting back” bit. We know that Jabber programming implies an event model. For this example, we’re going to use Tk, a widget library for building GUI applications, with bindings for many languages. Tk itself has an event model, which in many ways reflects Jabber’s. Table 9-3 shows how Jabber and Tk relate to each other in this programming model.

Table 9-3. Jabber and Tk event model reflections

Jabber	Tk
Establishing connection to server	Constructing widgets
Defining callbacks to handle incoming elements	Defining callbacks to handle UI events
Setting a “heartbeat” function[7]	Setting a command to execute regularly with the repeat() function
Launching the event loop	Starting MainLoop()
[7] See Section 9.3.4.3.

Having one program governed by two independent event loops ...