Question

我要感谢Andrew Thompson帮助我在代码中做到这一点。如何访问每个按钮的actionPerformed监听器？

代码应根据您按下的按钮移动屏幕上的“球”。

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

public class Lab2a extends JFrame {

Lab2a(){
    setTitle("Lab 1b - Application #2");
    Lab2Panel p = new Lab2Panel();
    add(p);
}

public static void main(String[] args){

Lab2 frame = new Lab2();
frame.setTitle("Lab2 Application # 1");
frame.setLocationRelativeTo(null);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(600, 400);
frame.setVisible(true);
}

}

class Lab2Panel extends JPanel{
Lab2Button canvas = new Lab2Button();
JPanel panel = new JPanel();

Lab2Panel () {

setLayout(new BorderLayout());

JButton leftButton = new JButton("left");
JButton rightButton = new JButton("right");
JButton upButton = new JButton("up");
JButton downButton = new JButton("down");

panel.add(leftButton);
panel.add(rightButton);
panel.add(upButton);
panel.add(downButton);

this.add(canvas, BorderLayout.CENTER);
this.add(panel, BorderLayout.SOUTH);

leftButton.addActionListener(new Lab2MoveBallListener(canvas));
rightButton.addActionListener(new Lab2MoveBallListener(canvas));
}


}

class Lab2Button extends JPanel {
int radius = 5;
int x = -1;
int y = -1;

protected void paintComponent(Graphics g){
    if (x<0 || y<0) {
        x = getWidth() / 2 - radius;
        y = getHeight() / 2 - radius;
    }
    super.paintComponent(g);
    g.drawOval(x,y, 2 * radius, 2 * radius);

}

    public void moveLeft(){

        x -= 5;
        this.repaint();
    }

    public void moveRight(){

        x += 5;
        this.repaint();
    }

    public void moveUp(){
        y += 5;
        this.repaint();
    }

    public void moveDown(){
        y -= 5;
        this.repaint();
    }


}

class Lab2MoveBallListener implements ActionListener{
    private Lab2Button canvas;

Lab2MoveBallListener(Lab2Button canvas) {
    this.canvas = canvas;
 }

public void actionPerformed(ActionEvent e){
    canvas.moveLeft();
}

}

Answer 1

由于您正在使用带有2个按钮的1个动作侦听器类，因此您必须有一种方法来判断按下了哪个按钮。你可以在actionPerformed方法中尝试这样的东西：

 public void actionPerformed(ActionEvent e) {
    if(e.getActionCommand().matches("left"))
      System.out.print("left button pressed");
    else if(e.getActionCommand().matches("right"))
      System.out.print("right button pressed");
}

另一种方法是通过这样做来创建一个匿名类：

 buttonLeft.addActionListener(new ActionListener(){
      public void actionPerformed(){
        //left button code
      }
    });

  buttonRight.addActionListener(new ActionListener(){
    public void actionPerformed(){
      //right button code
    }
  });

Answer 2

在ActionListener的actionPerformed(...)方法中，您可以获取通过ActionEvent的getActionCommand()方法按下的按钮文本。

试试看结果：

public void actionPerformed(ActionEvent e){
    String actionCommand = e.getActionCommand();

    System.out.println("actionCommand is: " + actionCommand);
}

现在你可以在这个方法中使用这些信息，而不仅仅是写出标准输出，但我会让你弄清楚其余的。

如何访问按钮的每个ActionPerformed？

2 个答案: