Question

I am having some trouble with my swingworker thread, and the issue is when i cancel. Essentially, I have a a start button, which when clicked runs my swingworker.

From here my swing worker does a number of small things but the main thing is that it completes some long running reflection calls.

I also have a cancel button – which as you probably guessed cancels my swingworker. The issue however is that I have a bug which I just cannot pinpoint.

After cancelling the application mid way through its first run, the swing worker cancels perfectly, however, if i then click start again and let it run all the way through when it completes – the thread seems to pick back up from where i cancelled on the first run :/ . I have no idea why this is and it apepears as if the cancelled thread is resuming and actually remembering state. I know this is happening because on my gui I have a JLabel that says “processing element 1 of 15…” and it jumps back to the cancelled point.

public class Test
{
    private SwingWorker<Object, Integer> swingworker = initiate(); 
    private void startListener()
    {
        start.addActionListener(new ActionListener ()
         {    
            public void actionPerformed(ActionEvent  e) 
            {             
                runIt();  
            }
        }); 
    }

    private void runIt()
    {
        try
        {
            if(swingworker .isDone())
                swingworker = getSwingWorker();

            swingworker.execute();
        }
        catch (HeadlessException e) { } 
        catch(Exception e){LogFileWriter.log(e);}
    }   


    private SwingWorker<Object, Integer> getSwingWorker()
    {
        return new SwingWorker<Object, Integer>() 
        {
            Object o;

             protected Object doInBackground() throws Exception 
             { 
                 //do some short calcs
                 doLongCalc();
                 return o;
             }

             protected void done()
             { 
                 if(!swingworker .isCancelled()) {} //chnage the gui values like enable / disable button } 
                 else{}//it was cancelled so stop progress bar and stuff

             }
        };   
    }

    private void cancelListener()
    {
        cancel.addActionListener(new ActionListener ()
         {    
            public void actionPerformed(ActionEvent e) 
            {

                if(swingworker.getState() == SwingWorker.StateValue.STARTED || swingworker.getState() == SwingWorker.StateValue.DONE)
                {
                    swingworker .cancel(true);
                }
            }
        }); 
    }

    private void doLongCalc()
    {
        //wrap the taks in checks for cancelled or not
        if(!swingworker.isCancelled())//do something
        if(!swingworker.isCancelled())//do something
        if(!swingworker.isCancelled())//do something
        if(!swingworker.isCancelled())//do something
    }
}

Answer 1

I had found out that I was not actually catching and dealing with an exception correctly. As such the programme flow was continuing where it should have been stopping.