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Re: Can you get this SwingWorker code to work more than once

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  To: clusardi2k
From: Eric Sosman <esosman@ieee-dot-org.invalid>

On 8/9/2012 11:55 AM, clusardi2k@aol.com wrote:
> On Thursday, August 9, 2012 11:48:04 AM UTC-4, Eric Sosman wrote:
>> On 8/9/2012 11:24 AM, ... wrote: > Here is a project that works
>> perfectly only the first time. [...] Quoth the JavaDoc: "SwingWorker is only
>> designed to be executed once. Executing a SwingWorker more than once will
not
>> result in invoking the doInBackground method twice." If you want to do a
>> background task N times, you'll need N instances of SwingWorker, one per
task
>> execution. -- Eric Sosman esosman@ieee-dot-org.invalid
>
> So, I want a project to do the following:
>
> (1) Display a button when the project is run,
> (2) When the user presses the button, a label is displayed.
> (3) The project next executes three long "for" loops such as in a previous
post of this thread.
> (4) When the three "for" loops are finished, the label disappears.
>
> Question: How can I repeatedly do steps (2) through (4) above when a project
is started?

     "When a project is started?"  Or "Each time the user presses
the button?"  I'll assume the latter.

     When you set up the button, create an ActionListener to be
notified of button presses.  The listener's actionPerformed() method will 
display the label (that's #2 above), create a SwingWorker, call the worker's 
execute() method, and return.

     Because execute() was called, Java will ("eventually," but in
practice "fairly soon") start the SwingWorker on a background thread and call 
its doInBackground() method.  This method runs the long loops (#3) and then 
returns.  Note that since it's executing on a background thread and not on the 
event dispatch thread (EDT), doInBackground() should do almost nothing to or 
with the GUI: Only a very few bits of Swing are thread-safe.

     After doInBackground() returns, Java will ("eventually/soon")
call the SwingWorker's done() method.  This call runs on the EDT, so the done() 
method can manipulate the GUI: It can make the label invisible or even remove 
it from its container (#4).

     Next time the user presses the button, the actionPerformed()
method creates a brand-new SwingWorker and the same sequence of actions 
repeats.  You can't re-use the old SwingWorker instance, but you can create a 
new instance of the same class, running the same code.

     All this and more is covered in the Java Tutorial's chapter
on Swing concurrency,

<http://docs.oracle.com/javase/tutorial/uiswing/concurrency/worker.html>

--
Eric Sosman
esosman@ieee-dot-org.invalid

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Can you get this SwingWorker code to work more than once "clusardi2k" <clusardi2k@1:261/38.remove-k2r-this> - 2012-08-09 18:44 +0000
  Re: Can you get this SwingWorker code to work more than once "Eric Sosman" <eric.sosman@1:261/38.remove-k2r-this> - 2012-08-09 18:44 +0000
    Re: Can you get this SwingWorker code to work more than once "clusardi2k" <clusardi2k@1:261/38.remove-k2r-this> - 2012-08-09 18:44 +0000
      Re: Can you get this SwingWorker code to work more than once "markspace" <markspace@1:261/38.remove-k2r-this> - 2012-08-09 18:44 +0000
      Re: Can you get this SwingWorker code to work more than once "Eric Sosman" <eric.sosman@1:261/38.remove-tos-this> - 2012-08-09 19:46 +0000
    Re: Can you get this SwingWorker code to work more than once "clusardi2k" <clusardi2k@1:261/38.remove-k2r-this> - 2012-08-09 18:44 +0000
      Re: Can you get this SwingWorker code to work more than once "Eric Sosman" <eric.sosman@1:261/38.remove-tos-this> - 2012-08-09 19:46 +0000
  Re: Can you get this SwingWorker code to work more than once "Knute Johnson" <knute.johnson@1:261/38.remove-k2r-this> - 2012-08-09 18:44 +0000

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