jLabel 不改变文本和 jProgressbar 不更新

Question

I have a JFrame . in the JFrame is a JDesktopPane , JComboBox , several JLabel s, and a JProgressBar . I am facing two challenges:

1. I want to update/change the text in one of the JLabel s in the JFrame by clicking a JButton that is on a JInternalFrame (the button does some calculations).

2. Upon clicking a JButton that is on another JInternalFrame (the button performs a small task), I want to use the JProgressBar (progressbar is in JFrame ) to show the progress of work done.

I use SwingUtilities.invokelater() to perform the tasks done by the buttons. am using NetBeans as my IDE.

Answer 1

Hard to know what is happening without code, but probably the Event Dispatch Thread (EDT) is being blocked (or terminated?), eg by code being called by invokeLater . The EDT is used to update the GUI and should not be used for (slow) non-GUI related calculations. See tutorial The Event Dispatch Thread and subsequent for more details.

Example (without blocking):

import java.awt.*;
import java.awt.event.ActionEvent;
import java.time.LocalTime;

import javax.swing.*;

public class LabelProgress {

    public static void main(String[] args) {
        LabelProgress main = new LabelProgress();
        SwingUtilities.invokeLater(() -> main.showInternal1());
        SwingUtilities.invokeLater(() -> main.showInternal2());
    }

    private JFrame frame;
    private JLabel label;
    private JDesktopPane desktop;
    private JProgressBar bar;

    private int progress = 0;

    private LabelProgress() {
        label = new JLabel("Label: ");

        desktop = new JDesktopPane();

        bar = new JProgressBar(0, 100);
        bar.setStringPainted(true);

        frame = new JFrame();
        frame.setLayout(new BorderLayout());
        frame.add(label, BorderLayout.BEFORE_FIRST_LINE);
        frame.add(desktop, BorderLayout.CENTER);
        frame.add(bar, BorderLayout.AFTER_LAST_LINE);
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.setSize(600, 400);
        frame.validate();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    private void showInternal1() {
        JButton change = new JButton("Change");
        change.addActionListener(this::doChange);

        JInternalFrame internal = new JInternalFrame("Change Label");
        internal.setLayout(new FlowLayout());
        internal.add(change);
        internal.setBounds(20, 20, 200, 150);
        internal.setVisible(true);
        desktop.add(internal);
    }

    private void showInternal2() {
        JButton task = new JButton("Task");
        task.addActionListener(this::doTask);

        JInternalFrame internal = new JInternalFrame("Small Task");
        internal.setLayout(new FlowLayout());
        internal.add(task);
        internal.setBounds(150, 100, 200, 150);
        internal.setVisible(true);
        desktop.add(internal);
    }

    private void doChange(ActionEvent ev) {
        // using a SwingWorker:
        // for demonstration I used an anonymous class, maybe a own class is better
        SwingWorker<LocalTime , Void> worker = new SwingWorker<LocalTime , Void>() {
            @Override
            protected LocalTime doInBackground() throws Exception {
                // not executed on the EDT - just get the current time
                LocalTime someCalculation = LocalTime.now();
                return someCalculation;
            }
            @Override
            protected void done() {
                // executed on EDT
                try {
                    LocalTime resultOfSomeCalculation = get();
                    label.setText("Label: " + resultOfSomeCalculation.toString());

                } catch (Exception ex) {
                    ex.printStackTrace();
                }
            }
        };
        worker.execute();
    }

    private void doTask(ActionEvent ev) {
        // no need to use SwingWorker
        Thread thread = new Thread(this::slowTask);
        thread.start();
    }

    private void slowTask() {
        // not really that slow, just for demonstration
        progress += 10;
        if (progress > 100) progress = 100;

        // and now switching to the EDT
        SwingUtilities.invokeLater(() -> bar.setValue(progress));
    }
}