Question

以下代码将向JFrame添加3个JLabel，然后删除3个JLabel。 2秒后，它将重新绘制3个JLabel。

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

@SuppressWarnings("serial")
public class RepaintFrameTest extends JFrame {
    private JPanel panel = new JPanel();
    private JLabel labelOne = new JLabel("label1");
    private JLabel labelTwo = new JLabel("label2");
    private JLabel labelThree = new JLabel("label3");
    public RepaintFrameTest() { 
        panel.add(labelOne);
        panel.add(labelTwo);
        panel.add(labelThree);
        add(panel);
        pack();
        setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        setSize(1024,768);
        setLocationRelativeTo(null);
        setVisible(true);
    }

    public static void main(String args[]) {
        RepaintFrameTest frameOne = new RepaintFrameTest();
        frameOne.getContentPane().removeAll();   
        frameOne.getContentPane().validate();
        frameOne.getContentPane().repaint();
        new Thread(new RepaintThread()).start();
    }
}

class RepaintThread implements Runnable {
    @Override
    public void run() {
        try   {              
            Thread.sleep(2000);            
        }catch (InterruptedException interruptedException)  {                           
            System.out.println( "Thread is interrupted when it is sleeping" +interruptedException);             
        } 
        RepaintFrameTest frameTwo = new RepaintFrameTest();
        frameTwo.getContentPane().validate();
        frameTwo.getContentPane().repaint();
    }
}

我遇到的一个小问题是它重新绘制到新帧（frameTwo）而不是旧帧（frameOne）。

如何制作它以重新绘制现有框架而不是重新绘制新框架？

Answer 1

Simpy使用CardLayout来交换视图。
使用Swing Timer而不是当前的后台线程，因为您当前的代码不是Swing线程安全的，并且存在有害的不可预测线程异常的风险。
我会给主要的JPanel添加CardLayout，然后添加一个JLabel，其中包含一个合适的String常量的JPanel。
然后我使用JPanel添加到主CardLayout，这是一个空的JLabel，在add方法中使用另一个String常量。即，add(new JLabel(), BLANK_COMPONENT);
然后在我的Swing Timer中，只需在我的CardLayout对象上调用next()，传入主要的CardLayout-using组件：cardLayout.next(myMainJPanel);

例如，

import java.awt.CardLayout;
import java.awt.Dimension;
import java.awt.event.*;

import javax.swing.*;

public class RepaintTest extends JPanel {
   private static final int PREF_W = 400;
   private static final int PREF_H = PREF_W;
   private static final int LABEL_COUNT = 3;
   private static final String LABEL_PANEL = "label panel";
   private static final Object BLANK_COMPONENT = "blank component";
   private static final int TIMER_DELAY = 2000;
   private CardLayout cardLayout = new CardLayout();

   public RepaintTest() {
      JPanel labelPanel = new JPanel();
      for (int i = 0; i < LABEL_COUNT; i++) {
         labelPanel.add(new JLabel("Label " + (i + 1)));
      }

      setLayout(cardLayout);
      add(labelPanel, LABEL_PANEL);
      add(new JLabel(), BLANK_COMPONENT);

      new Timer(TIMER_DELAY, new TimerListener()).start();

   }

   @Override
   public Dimension getPreferredSize() {
      return new Dimension(PREF_W, PREF_H);
   }

   private class TimerListener implements ActionListener {
      @Override
      public void actionPerformed(ActionEvent e) {
         cardLayout.next(RepaintTest.this);
      }
   }

   private static void createAndShowGui() {
      RepaintTest mainPanel = new RepaintTest();

      JFrame frame = new JFrame("RepaintTest");
      frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}

Answer 2

您违反了Swing的单线程规则......

有关详细信息，请参阅Concurrency in Swing。

基本上，您不应该从事件调度线程以外的任何线程上下文更新任何UI组件。

相反，您应该使用SwingWorker，或者可能更适合您的问题javax.swing.Timer

问题是，正如您已经清楚注意到的那样，frameTwo的引用与frameOne的引用无关，它们是完全独立的对象，因此每个引用都没有任何共同点。其他

您需要做的是将您想要更新的对象的某种引用传递给进行更新的类......

在此示例中，我只是在reapplyLabels中创建了RepaintFrameTest方法，并使用Swing Timer设置为2秒延迟，以调用此方法...

就个人而言，我更倾向于传递一个interface，因为它暴露较少并且解耦代码，但这只是一个简单的例子......

import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.Timer;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class RepaintFrameTest extends JFrame {

    private JPanel panel = new JPanel();
    private JLabel labelOne = new JLabel("label1");
    private JLabel labelTwo = new JLabel("label2");
    private JLabel labelThree = new JLabel("label3");

    public RepaintFrameTest() {
        add(panel);
    }

    public void reapplyLabels() {
        panel.add(labelOne);
        panel.add(labelTwo);
        panel.add(labelThree);

        revalidate();
        repaint();
    }

    public static void main(String args[]) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                RepaintFrameTest frame = new RepaintFrameTest();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setSize(400, 400);
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);

                Timer timer = new Timer(2000, new RepaintAction(frame));
                timer.setRepeats(false);
                timer.start();
            }
        });
    }

    public static class RepaintAction implements ActionListener {

        private RepaintFrameTest frame;

        public RepaintAction(RepaintFrameTest frame) {
            this.frame = frame;
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            frame.reapplyLabels();
        }
    }

}

虽然没有足够的背景来进行完整的judement调用，但我也同意HovercraftFullOfEels，CardLayout会达到相同的结果，可能会减少混乱......

再次更新JFrame

2 个答案: