java - 3 个 JButton 无法触发 3 个绘制图像

Question

我正在尝试创建一个具有边框布局、3 个 jbutton 和 Paint 的 drawImage 组件的项目，以创建一个监听按钮按下并更改图像的红绿灯。我知道条件语句中的绘制图像有效，因为如果我取出 if 语句，图像看起来很好，并且我知道 Action 监听器有效，因为我使用 joptionpane 对话框测试了每个图像。然而，在当前的形式中，按下按钮时没有任何反应，我不确定为什么。任何帮助将不胜感激，我正在学习!

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class TrafficLight extends JFrame implements ActionListener
{
//establishes panel, button, and boolean variables
 private JPanel pN, pS, pE, pW, pC;

 private JButton btnWait, btnGo, btnStop;

 private boolean redIlluminated = false , greenIlluminated = false , yellowIlluminated = false;

public static void main(String[] args)
{
    TrafficLight frame = new TrafficLight();
    frame.setSize(750, 850);
    frame.createGUI();
    frame.setVisible(true);

}

private void createGUI()
{
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    Container window = getContentPane();

    window.setLayout(new BorderLayout());

    //custom colors
    Color slate=new Color(49, 58, 58);
    Color eggshell=new Color(230, 226, 222);
    Color easterPink=new Color(249, 170, 170);
    Color salmon=new Color(201, 80, 65);
    Color dusk=new Color(187, 185, 184);
    Color billiards=new Color(71, 88, 68);

    //custom fonts
    Font buttonFont = new Font("SansSerif", Font.BOLD, 20);

    //sets up north jpanel 
    pN = new JPanel();
    pN.setPreferredSize(new Dimension(680,45));
    pN.setBackground(eggshell);
    window.add (pN, BorderLayout.NORTH);

    //button formatting
    //establishes go button, font, color, and click event, then adds it to pN panel
    btnGo = new JButton ("GO");
    btnGo.setFont(buttonFont);
    btnGo.setBackground(dusk);
     btnGo.addActionListener(
        new ActionListener()
        {
            public void actionPerformed(ActionEvent ae)
            {
                //trigger condition change here to cause the paint event below
              greenIlluminated = true;
            }
        }
    );
    pN.add(btnGo);

    //establishes wait button, font, color, and click event, then adds it to pN panel
    btnWait = new JButton("WAIT"); 
    btnWait.setFont(buttonFont);
    btnWait.setBackground(dusk);
    btnWait.addActionListener(
        new ActionListener()
        {
            public void actionPerformed(ActionEvent ae)
            {
               //trigger condition change here to cause the paint event below 
              yellowIlluminated = true;
            }
        }
    );
    pN.add(btnWait);

    //establishes stop button, font, color, and click event, then adds it to pN panel
    btnStop = new JButton("STOP");
    btnStop.setFont(buttonFont);
    btnStop.setBackground(dusk);
    btnStop.addActionListener(
        new ActionListener()
        {
            public void actionPerformed(ActionEvent ae)
            {
                //trigger condition change here to cause the paint event below
              redIlluminated = true;
            }
        }
    );
    pN.add(btnStop);

    //east jpanel for stoplight
    pE = new JPanel();
    pE.setPreferredSize(new Dimension(272,318));
    pE.setBackground(billiards);
    window.add (pE, BorderLayout.EAST);

    //west jpanel
    pW = new JPanel();
    pW.setPreferredSize(new Dimension(136,318));
    pW.setBackground(billiards);
    window.add (pW, BorderLayout.WEST);

    //center jpanel for car
    pC = new JPanel();
    pC.setPreferredSize(new Dimension(272,318));
    pC.setBackground(slate);
    window.add (pC, BorderLayout.CENTER);

    //south jpanel
    pS = new JPanel();
    pS.setPreferredSize(new Dimension(680, 15));
    pS.setBackground(eggshell);
    window.add (pS, BorderLayout.SOUTH);
}

public void actionPerformed(ActionEvent click) {


    }

public void paint(Graphics g) {
    super.paint(g);
    //draws stoplight
    g.drawImage(new ImageIcon(getClass().getResource("red1.png")).getImage(), 460, 150, this);
    g.drawImage(new ImageIcon(getClass().getResource("green1.png")).getImage(), 460, 272, this);
    g.drawImage(new ImageIcon(getClass().getResource("yellow1.png")).getImage(), 460, 373, this);

    //draws car in center
    g.drawImage(new ImageIcon(getClass().getResource("car.png")).getImage(), 150, 600, this);

    //sets conditions to show images on button click based on boolean logic changed by buttons
    if (redIlluminated)
    {
        g.drawImage(new ImageIcon(getClass().getResource("red2.png")).getImage(), 460, 150, this);
    }

    else if (greenIlluminated)
    {
        g.drawImage(new ImageIcon(getClass().getResource("green2.png")).getImage(), 460, 272, this);
    }
    else if (yellowIlluminated)
    {
        g.drawImage(new ImageIcon(getClass().getResource("yellow2.png")).getImage(), 460, 373, this);
    }
     }

}

Answer 1

不确定是否仍然与您相关，但以防万一其他人偶然发现这个问题......

Swing 容器不会持续监听其图形的更改，因此当您进行更改时，您需要确保调用 repaint() 以便再次渲染整个容器。

在按钮的 ActionListener 中添加一个方法调用如下所示:

btnGo.addActionListener( new ActionListener() {

        public void actionPerformed(ActionEvent ae) {

          //trigger condition change here to cause the paint event below, I turn off the other flags so that the if clause in the paint method knows exactly what to paint 
          greenIlluminated = true;
          redIlluminated = false;
          yellowIlluminated = false;

          //This is the one method that triggers a call to the paint method you overrode
          repaint();
       }
});

并且需要对其他 ActionListener 进行类似的更改。

<小时/>

顺便说一句，如果您要为按钮使用匿名 ActionListener 类的对象，则无需实现 ActionListener 接口(interface)。