Question

我正在创建一种待办事项列表应用程序。一方面，您有待办事项列表应用程序，其中包含可以添加任务的框，另一方面，您有一个数字时钟。待办事项清单完美地运作和显示。另一方面，时钟根本不显示。当我在测试程序中单独实例化一个Clock对象时，它运行得很好，但是当我尝试使用待办事项列表在JFrame中实例化它时，它根本就不显示。我已经检查了我的驱动程序，并且我有我的时钟对象的实例化和声明。我做错了什么？

ClockPanel对象：

 import java.awt.Color;
 import java.awt.Font;
 import java.awt.event.ActionEvent;
 import java.awt.event.ActionListener;
 import java.text.SimpleDateFormat;
 import java.util.Date;
 import javax.swing.Timer;

 public class ClockPanel extends javax.swing.JPanel implements ActionListener{
    private SimpleDateFormat sdf = new SimpleDateFormat("hh:mm:ss");
    private Timer timer;
    private javax.swing.JLabel clockLabel = new javax.swing.JLabel();
    public ClockPanel() {
     super();

     clockLabel.setText(sdf.format(new Date(System.currentTimeMillis())));
     clockLabel.setFont(new Font("Monospaced", Font.BOLD, 100));
     clockLabel.setOpaque(true);
     clockLabel.setBackground(Color.black);
     clockLabel.setForeground(Color.white);

     timer = new Timer(500, this);
     timer.setRepeats(true);
     timer.start();

     clockLabel.setVisible(true);

     initComponents();
  }
  @Override
  public void actionPerformed(ActionEvent e){
     if(e.getSource().equals(timer))
        clockLabel.setText(sdf.format(new Date(System.currentTimeMillis())));
  }
  @SuppressWarnings("unchecked")
  // <editor-fold defaultstate="collapsed" desc="Generated Code">//GEN-BEGIN:initComponents
  private void initComponents() {

     javax.swing.GroupLayout layout = new javax.swing.GroupLayout(this);
     this.setLayout(layout);
     layout.setHorizontalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGap(0, 400, Short.MAX_VALUE)
        );
     layout.setVerticalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGap(0, 300, Short.MAX_VALUE)
        );
  }// </editor-fold>//GEN-END:initComponents
// Variables declaration - do not modify//GEN-BEGIN:variables
// End of variables declaration//GEN-END:variables
 }

Clock对象本身：

import java.text.SimpleDateFormat;
import java.util.Date;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Clock extends JLabel implements ActionListener{
  private SimpleDateFormat sdf = new SimpleDateFormat("hh:mm:ss");
  private Timer timer;
  public Clock(){
     super();

     setText(sdf.format(new Date(System.currentTimeMillis())));
     setFont(new Font("Monospaced", Font.BOLD, 100));
     setOpaque(true);
     setBackground(Color.black);
     setForeground(Color.white);

     timer = new Timer(500, this);
     timer.setRepeats(true);
     timer.start();

     setVisible(true);
  }
  public void actionPerformed(ActionEvent e){
     if(e.getSource().equals(timer))
        setText(sdf.format(new Date(System.currentTimeMillis())));
  }
 }

Answer 1

clockLabel永远不会添加到任何布局组中。这个SSCCE解决了这个问题。

ClockPanel

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.SimpleDateFormat;
import java.util.Date;

import javax.swing.*;
import javax.swing.GroupLayout.ParallelGroup;

public class ClockPanel extends JPanel implements ActionListener {

    private static final long serialVersionUID = 1L;
    private SimpleDateFormat sdf = new SimpleDateFormat("hh:mm:ss");
    private Timer timer;
    private JLabel clockLabel = new JLabel("Ha Ha");

    public ClockPanel() {
        super();

        clockLabel.setText(sdf.format(new Date(System.currentTimeMillis())));
        clockLabel.setFont(new Font("Monospaced", Font.BOLD, 100));
        clockLabel.setOpaque(true);
        clockLabel.setBackground(Color.black);
        clockLabel.setForeground(Color.white);

        timer = new Timer(500, this);
        timer.setRepeats(true);
        timer.start();

        initComponents();
    }

    @Override
    public void actionPerformed(ActionEvent e){
        if(e.getSource().equals(timer))
            clockLabel.setText(sdf.format(
                new Date(System.currentTimeMillis())));
    }

    private void initComponents() {

        GroupLayout layout = new GroupLayout(this);
        ParallelGroup parallelGroupH = layout.createParallelGroup(
                GroupLayout.Alignment.LEADING);
        this.setLayout(layout);
        layout.setHorizontalGroup(
                parallelGroupH
                .addGap(0, 400, Short.MAX_VALUE)
                );
        ParallelGroup parallelGroupV = layout.createParallelGroup(
                GroupLayout.Alignment.LEADING);
        layout.setVerticalGroup(
                parallelGroupV
                .addGap(0, 30, Short.MAX_VALUE)
                );
        parallelGroupH.addComponent(clockLabel);
        parallelGroupV.addComponent(clockLabel);
    }

    public static void main(String[] args) throws Exception {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                JOptionPane.showMessageDialog(null, new ClockPanel());
            }
        });
    }
}

无法显示javax.swing组件，尤其是JPanel

1 个答案: