Swing Hacks

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Chapter 1, Basic JComponents

#8 Animate Transitions Between Tabs

HACK

The last line of the main( ) method starts a new thread to manage the back-

ground image.

Because the code is completely encapsulated in the

BackgroundLoader class, you could add space images to a

component that uses a scroll pane, not just a

JTextArea.

H A C K

#8

Animate Transitions Between Tabs Hack #8

This hack shows how to create animated transitions that play whenever the

user switches tabs on a

JTabbedPane.

One of Swing’s great strengths is that you can hack into virtually anything.

In particular, I love making changes to a component’s painting code. The

ability to do this is one of the reasons I prefer Swing over SWT. Swing gives

me the freedom to create completely new UI concepts, such as transitions.

With the standard paint methods, Swing provides most of what you will

need to build the transitions. You will have to put together three additional

things, however. First, you need to find out when the user actually clicked

on a tab to start a transition. Next, you need a thread to control the anima-

tion. Finally, since some animations might fade between the old and new

tabs, you need a way to provide images of both tabs at the same time. With

those three things, you can build any animation you desire.

Building a Basic Tabbed Pane

To keep things tidy, I have implemented this hack as a subclass of

JTabbedPane, except for the actual animation drawing, which will be dele-

gated to a further subclass. By putting all of the heavy lifting into the parent

class, you will be able to create new animations easily.

Example 1-16 is the basic skeleton of the parent class.

frame.pack( );

frame.show( );

new Thread(new BackgroundLoader(viewport)).start( );

}

Example 1-16. A skeleton for the transition manager

public class TransitionTabbedPane extends JTabbedPane

implements ChangeListener, Runnable {

protected int animation_length = 20;

Example 1-15. Testing the space image background (continued)