Showing GlassPane before entering loop

Question

(In my applicaton with Swing GUI) I want to display GlassPane during some work performed in a loop or method, which is called after clicking JButton.

For example: (action performed after clicking a button)

if (item.equals(button)) {

    glassPane.setVisible(true);

    someTimeConsumingMethod();

    glassPane.setVisible(false);

}

Running this code results in not showing the glassPane during execution of someTimeConsumingMethod() - GUI just freezes for a moment, before result is displayed. Removing last line in that loop (glassPane.setVisible(false);) results in showing glassPane after the method is done (when GUI unfreezes).

Is there a simple way to show that glassPane before GUI freezes, or I need to use some advanced knowledge here? (threads?)

UPDATE1:

I've updated my code according to davidXYZ answer (with two changes):

(action performed after clicking a button)

if (item.equals(button)) {

    glassPane.setVisible(true);

        new Thread(new Runnable(){
            public void run(){
                someTimeConsumingMethod(); // 1st change: running the someTimeConsumingMethod in new Thread
                                           //             instead of setting glassPane to visible
            }
        }).start();

    // 2nd change: moved glassPane.setVisible(false); inside the someTimeConsumingMethod(); (placed at the end of it).

}

The point of 1st change is that setting glassPane visible in new thread right before running someTimeConsumingMethod in my GUI thread was revealing the glassPane after someTimeConsumingMethod finished (double-checked this).

Now it works fine, thank you for all answers. I will definitely check all the links you provided to actually understand threads!

UPDATE2: Some more info: someTimeConsumingMethod(); in my application is prepering new Swing Components accoriding to the XML data (cards builded from JButtons and JLabels with few JPanels where needed, and adding them in correct places).

UPDATE3: I am trying to make it work using SwingWorker's invokeLater method. Now it looks like that:

(action performed after clicking a button)

if (item.equals(button)) {

    glassPane.setVisible(true);

    SwingUtilities.invokeLater(new Runnable() {
        @Override
        public void run() { 
            someTimeConsumingMethod();
            glassPane.setVisible(false);
        }
    });

}

It works not that good as code from UPDATE1 (but still - it works). Problems are:

• glassPane loads without .gif animation (file is setted up in custom glassPane class - it works with UPDATE1 code)

• there is small delay at the end of "working" process - first cursor changes to normal (from the WAIT_CURSOR), and after very short moment glassPane disappear. Cursor is changed by the custom glassPane class on activation/deactivation (no delay using new Thread way).

Is it correct way of using SwingWorker's invokeLater method?

EDIT: My mistake, I confused SwingWorker with SwingUtilities.invokeLater(). I guess the image issue is due to GUI freezing when the someTimeCOnsumingMethod starts.

Answer 1

GUI just freezes for a moment, before result is displayed. Removing last line in that loop (glassPane.setVisible(false);) results in showing glassPane after the method is done (when GUI unfreezes).

this is common issue about Event Dispath Thread, when all events in EDT are flushed to the Swing GUI in one moment, then everything in the method if (item.equals(button)) { could be done on one moment,

but your description talking you have got issue with Concurency in Swing, some of code blocking EDT, this is small delay, for example Thread.sleep(int) can caused this issue, don't do that, or redirect code block to the Backgroung taks

Is there a simple way to show that glassPane before GUI freezes, or I need to use some advanced knowledge here? (threads?)

this question is booking example why SwingWorker is there, or easier way is Runnable#Thread

• methods implemented in SwingWorker quite guarante that output will be done on EDT

• any output from Runnable#Thread to the Swing GUI should be wrapped in invokeLater()

easiest steps from Jbuttons Action could be

• show GlassPane

• start background task from SwingWorker (be sure that listening by PropertyChangeListener) or invoke Runnable#Thread

• in this moment ActionListener executions is done rest of code is redirected to the Backgroung taks

• if task ended, then to hide GlassPane

• create simple void by wrapping setVisible into invokeLater() for Runnable#Thread

• in the case that you use SwingWorker then you can to hide the GlassPane on proper event from PropertyChangeListener or you can to use any (separate) void for hidding the GlassPane

best code for GlassPane by @camickr, or my question about based on this code

Answer 2

You are blocking the EDT (Event Dispatching Thread, the single thread where all UI events are handled) with your time consuming job.

2 solutions:

1. Wrap the calls to:someTimeConsumingMethod();glassPane.setVisible(false); in SwingUtilities.invokeLater(), this will allow the frame to repaint itself once more. However this will still freeze your GUI.

2. Move your someTimeConsumingMethod() into a SwingWorker (this is the recommended option). This will prevent your GUI from ever freezing.

Read the javadoc of SwingWorker to understand better what is going on and how to use it. You may also learn a lot in this tutorial about Swing and multi-threading

Answer 3

 JButton startB = new JButton("Start the big operation!");
    startB.addActionListener(new ActionListener() {
      public void actionPerformed(java.awt.event.ActionEvent A) {
        // manually control the 1.2/1.3 bug work-around
        glass.setNeedToRedispatch(false);
        glass.setVisible(true);
        startTimer();
      }
    });

glasspane here used here is FixedGlassPane glass;

ref: http://www.java2s.com/Code/Java/Swing-JFC/Showhowaglasspanecanbeusedtoblockmouseandkeyevents.htm

Answer 4

Guillaume is right. When you are on the main thread, each line will finish before the next line. You definitely need another thread.

An easy way to solve your problem is to spin off the display of the glasspane in another thread (normal thread or Swing threads - either will work fine).

if (item.equals(button)) {
    new Thread(new Runnable(){
        public void run(){
            glassPane.setVisible(true);
        }
    }).start();
    someTimeConsumingMethod();
    glassPane.setVisible(false);
}

That way, a different thread is blocked by setvisible(true) while someTimeConsumingMethod() runs on the main thread. When it's done, glasspane will disappear. The anonymous thread reaches the end of the run method and stops.