更改Java SWT标签时出现无效的线程访问错误

Question

I want to run my program where the value of a label changes after the Timer goes off. But whenever the Timer runs I will keep getting the Invalid Thread access error and my label does not get updated.

protected void createContents() {
    <--GUI codes -->

    //Timer set to go every 10 seconds
      ActionListener taskPerformer = new ActionListener() {
          public void actionPerformed(ActionEvent evt) {
              System.out.println("Timer");

              lblState.setText("On");
          }
      };
      new Timer(delay, taskPerformer).start();
}

Answer 1

This link from the SWT FAQ explains the error and how to solve it: any code that modifies GUI components (in your case, setting the text of the label) needs to run on the display thread, otherwise this error will occur.

To run on the display thread, wrap the code inside a Runnable and call Display.getDefault().syncExec( with the provided Runnable :

Display.getDefault().syncExec(new Runnable() {
    public void run() {
        // code that affects the GUI
    }
});

Answer 2

All access to UI objects must be done in the user interface thread. You can do this using Display.asyncExec (or Display.syncExec ).

Change your line:

lblState.setText("On");

to

Display.getDefault().asyncExec(() -> lblState.setText("On"));

for Java 8. For Java 7 or earlier use:

Display.getDefault().asyncExec(new Runnable() {
   @Override
   public void run() 
   {
     lblState.setText("On");
   }
});