Swing Hacks

470

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Chapter 12, Miscellany

#93 Code Models That Don’t Block

HACK

Exposing the Threading

But what if a caller wants to manage threading? You might want to at least

expose the fact that a thread is still updating and have the rest of your code

be aware of that state.

Notice that the

NonBlockingURLDocument exposes a pair of extra methods—

isAlive( ) and getProgress( )—that aren’t required by Document or anything

else in

javax.swing.text. These are extra methods I tossed into the demo to

support the progress bar mentioned earlier in this hack.

The strategy here is to have an outside caller periodically check in on the

NonBlockingURLDocument, get its progress, and update a progress bar. Notice I

said periodically: this is a job for

javax.swing.Timer! Using the Swing timer,

you get regular callbacks, and your code is guaranteed to be on the event-

dispatch thread.

So, uncomment the

makeProgressBarUpdaterFor( ) call shown earlier, and

add this implementation of that method, along with a helper method:

Figure 12-8. Progressive self-update of a JTextArea’s document

Code Models That Don’t Block #93

Chapter 12, Miscellany

|

471

HACK

private void makeProgressBarUpdaterFor (NonBlockingURLDocument nbud) {

final NonBlockingURLDocument updatingDoc = nbud;

updateProgressBar (0);

ActionListener callback = new ActionListener( ...