java - 尝试显示计时器计数，drawString 方法无法正常工作

Question

我试图显示计时器计数，但它没有显示，但其他一切正常。谢谢你的帮助顺便说一句。

import javax.swing.*;

import java.util.*;
import javax.swing.Timer;

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class Tester {

static Timer timer;
static JFrame frame;
static JPanel panel;

public static void init(){
    frame = new JFrame();

    panel = new JPanel();

    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true);
    frame.setSize(500, 500);

    frame.add(panel);


}

上面的方法只是为了让代码更简洁。

public static void main(String[] args) {

init();


    class Clicker extends JPanel{

        int timesClicked;

        public Clicker(){
            timesClicked = 0;
        }

        void updateClicks(){
            timesClicked++;
            repaint();
        }

         public void paintComponent(Graphics g){
             super.paintComponent(g);
             Graphics2D g2 = (Graphics2D) g;
            System.out.println("Called!!!");
            g2.drawString("Half Seconds: "+timesClicked, 100, 100);

        }

    } //end of Clicker

上面的drawString方法不起作用。
最终 Clicker c = new Clicker(); 面板.add(c);

class TimeChecker implements ActionListener{

        @Override
        public void actionPerformed(ActionEvent e) {
            System.out.println("Clicked!");
            c.updateClicks();
        }

    }// end of TimeChecker

    ActionListener listener = new TimeChecker();
    timer = new Timer(500,listener);
    timer.start();



}

}

Answer 1

您遇到了多种问题

• Clicker 从未真正添加到任何内容
• panel 默认情况下使用 FlowLayout，但 Clicker 不提供大小调整提示，因此其大小为 0x0
• 您的代码通常设置有点奇怪。我会非常非常快地学会如何摆脱static。

快速且快速的解决方案...

将panel的布局管理器更改为BorderLayout...

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;

public class Test {

    static Timer timer;
    static JFrame frame;
    static JPanel panel;

    public static void init() {
        frame = new JFrame();

        panel = new JPanel(new BorderLayout());

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
        frame.setSize(500, 500);

        frame.add(panel);

    }

    public static void main(String[] args) {

        init();

        class Clicker extends JPanel {

            int timesClicked;

            public Clicker() {
                timesClicked = 0;
            }

            void updateClicks() {
                timesClicked++;
                repaint();
            }

            public void paintComponent(Graphics g) {
                super.paintComponent(g);
                Graphics2D g2 = (Graphics2D) g;
                System.out.println("Called!!!");
                g2.setColor(Color.BLACK);
                g2.drawString("Half Seconds: " + timesClicked, 100, 100);

            }

        } //end of Clicker

        final Clicker c = new Clicker();
        panel.add(c);
        panel.revalidate();
        panel.repaint();

        class TimeChecker implements ActionListener {

            @Override
            public void actionPerformed(ActionEvent e) {
                System.out.println("Clicked!");
                c.updateClicks();
            }

        }// end of TimeChecker

        ActionListener listener = new TimeChecker();
        timer = new Timer(500, listener);
        timer.start();

    }

}

稍微不同的方法(没有静态)

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Test {

    public static void main(String[] args) {
        new Test();
    }

    public Test() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                Clicker clicker = new Clicker();
                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(clicker);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);

                class TimeChecker implements ActionListener {

                    @Override
                    public void actionPerformed(ActionEvent e) {
                        System.out.println("Clicked!");
                        clicker.updateClicks();
                    }

                }// end of TimeChecker

                ActionListener listener = new TimeChecker();
                Timer timer = new Timer(500, listener);
                timer.start();

            }
        });
    }

    public class Clicker extends JPanel {

        private int timesClicked;

        public Clicker() {
            timesClicked = 0;
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(400, 200);
        }

        void updateClicks() {
            timesClicked++;
            repaint();
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2 = (Graphics2D) g;
            System.out.println("Called!!!");
            g2.setColor(Color.BLACK);
            g2.drawString("Half Seconds: " + timesClicked, 100, 100);

        }

    }

}