Path: csiph.com!newsfeed.hal-mli.net!feeder3.hal-mli.net!newsfeed.hal-mli.net!feeder1.hal-mli.net!eternal-september.org!feeder.eternal-september.org!mx04.eternal-september.org!.POSTED!not-for-mail From: Eric Sosman Newsgroups: comp.lang.java.programmer Subject: Re: Can you get this SwingWorker code to work more than once Date: Thu, 09 Aug 2012 14:29:34 -0400 Organization: A noiseless patient Spider Lines: 53 Message-ID: References: <4cc76fc2-fffc-470d-b4c6-0be778070523@googlegroups.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Injection-Date: Thu, 9 Aug 2012 18:29:38 +0000 (UTC) Injection-Info: mx04.eternal-september.org; posting-host="ffb8f7085759b339c1002252b48331a4"; logging-data="32536"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX18HZVHaPvRzOi8eMOc0Ncch" User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:14.0) Gecko/20120713 Thunderbird/14.0 In-Reply-To: <4cc76fc2-fffc-470d-b4c6-0be778070523@googlegroups.com> Cancel-Lock: sha1:Pd2LK7GoR7BseN1uwo/fIS7+LcA= Xref: csiph.com comp.lang.java.programmer:17462 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, -- Eric Sosman esosman@ieee-dot-org.invalid