如何使用JButtons启动和暂停SwingWorker线程

Question

I'm trying to learn Threads in Swing.

I have a Frame with a JProgressBar (progress), five JButtons (Start, Suspend, Resume, Cancel, Close), and a JLabel (label1).

The frame opens. Only Start is enabled. Start calls my class Progressor:

Updated Again Once and For All

Progressor progressor; //declared as class variable, initialized new in constructor and again in overridden done method

Here's the ButtonListener class:

public class ButtonListener implements ActionListener{
    public void actionPerformed(ActionEvent e)
    {

        if (e.getSource() == jbStart) {
            progressor.execute();
            label1.setText("Progressing ...");
            jbCancel.setEnabled(true);
            jbResume.setEnabled(true);
            jbSuspend.setEnabled(true);
            jbClose.setEnabled(true);
        }
        if(e.getSource() == jbCancel) {
            progressor.cancel(true);
            label1.setText("Progress Canceled");
        }
        if (e.getSource() == jbSuspend) {
            label1.setText(progressor.suspendProgress());
        }
        if (e.getSource() == jbResume) {
            label1.setText(progressor.resumeProgress());
        }
        if (e.getSource() == jbClose) {
            dispose();
        }

    }

}//buttonlistener

Here's the SwingWorker class:

public class Progressor extends SwingWorker<Void, Integer> {

    private volatile boolean suspend = false;
    private Object lock = new Object();

    @Override
    protected Void doInBackground() {

        for (int i = 0; i <= 10; i++) {
            checkForSuspend();
            try {
                Thread.sleep(1000);
            }
            catch (InterruptedException e) {
            }
            publish(i);
        }   
        return null;
    }

    @Override
    protected void process(List<Integer> list) {
        int value = list.get(list.size() - 1);
        progress.setValue(value);

    }

    public void checkForSuspend() {
        synchronized (lock) {
            while (suspend) {
                try {
                    lock.wait();
                } catch (InterruptedException ie){
                }
            }
        }
    }//checkForSuspend

    @Override
    protected void done() {
        label1.setText("All Done.  Press close to exit");
        progressor = new Progressor();
    }

    public synchronized String suspendProgress() {
        suspend = true;
        return "Progress suspended ...";
    }

    public synchronized String resumeProgress() {
        synchronized (lock) {
            suspend = false;
            lock.notify();
            return "Progress resumed ...";
        }
    }


}//Progressor class

Everything works except the cancel doesn't doesn't actually cancel the thread (the progress bar continues).

Should I suspend it before canceling?

Answer 1

This How to Pause and Resume a Thread in Java from another Thread question looks very similar to yours and has some nice examples in the answers.

As for your own code and why it does not work:

1. You create a new progressor on every click. You should be using and controlling one, instead of creating new ones every time.

2. When suspending your progressor finishes work instead of suspending. As the above question states - you should be looking at the flag at some points of your computation and acting on it. Example:

    while (!cancel) { if (!suspended) { for (int i = 1; i <= 10; i++) { Thread.sleep(1000); publish(i); } } } 

   The above code will suspend when it next reaches 10 (unless you resumed it before that), and finish when you press cancel (Cancel needs to be added as an extra flag in the obvious manner).

Answer 2

Your thread should run inside a while loop that looks for a boolean to change value from another object, then simply change the state with setPause(true/false) when you click the button:

while(true){
    if(object_everyone_can_reference.getPause()){
    Thread.sleep(1000);
     }

 }