如何在ActionListener正在进行时更新swing UI

Question

In my code below I want the TextArea to be cleared while the application is loading data. I also added a repaint() but still it's not cleared. Do I have to notify it differently to force a repaint?

    button.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent event) {
            textArea.setText("");
            textArea.repaint();


            String result = //call a REST API
            textArea.setText(result);
        }
    });

Answer 1

What I think you want to do is calling the rest api in another Thread. You can do it with a SwingWorker that is designed to run heavily task in another thread without blocking the gui. Here is a complete example i really like Swing Worker Example

Example:

class Worker extends SwingWorker<Void, String> {

    @Override
    protected Void doInBackground() throws Exception {
       //here you make heavy task this is running in another thread not in EDT
       // call REST API here

      return null;
    }

   @Override
   protected void done() {
        //this is executed in the EDT
        //here you update your textArea with the result
   }
}

After the doInBackground method is finished the done method is executed. Then SwingWorker notifies any PropertyChangeListeners about the state property change to StateValue.DONE . So you can override this method here or use a propertyChangeListener implementation to do what you want.

Answer 2

Just do the time-consuming operation in another thread. You can use SwingWorker , which will notify AWT thread as soon as the computation completes.

public void actionPerformed(ActionEvent event) {
    textArea.setText("");

    SwingWorker<String, Object> worker = new SwingWorker<String, Object>() {
        @Override
        protected String doInBackground() throws Exception {                
            return ...; // call a REST API
        }
        @Override
        protected void done() {
            try {
                textArea.setText(get());
            } catch (Exception e) {
                //ignore
            }
        }
    };      
    worker.execute();
}

You can also use invokeLater , which will execute the REST call as a part of the event queue.

public void actionPerformed(ActionEvent event) {
    textArea.setText("");

    SwingUtilities.invokeLater(new Runnable() {
        public void run() {
            String result = // call a REST API
            textArea.setText(result);
        }
    });
}

Answer 3

You run your actionPerformed(ActionEvent event) method in EDT because of that you can't update UI. For updating UI from your code try to use SwingWorker , it can update UI while background process running.

Or you can try to use Executors for background process and updating UI from EDT.