Question

我想沿着x轴向右或向左移动一个球，具体取决于用户点击的JButton。单击任一JButton时，球不会移动。

我已经使用System.out.println（）来尝试找出错误，并且程序正在检测JButtons上的点击并更改必须更改的变量（int horizontal）以移动球。

MoveBallPanel类：

package test;

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

public class MoveBallPanel extends JPanel implements ActionListener {

// declarations

private JButton moveLeft;
private JButton moveRight;
private int center;
private int horizontal;

public MoveBallPanel() {

    // make elements

    moveLeft = new JButton("To the left");
    moveLeft.addActionListener(this);
    moveRight = new JButton("To the right");
    moveRight.addActionListener(this);

    // add to panel

    add(moveLeft);
    add(moveRight);
}

// to do when JButton is clicked

@Override
public void actionPerformed(ActionEvent e) {

    final int MOVE = 50;

    if (e.getSource() == moveLeft) {
        horizontal -= MOVE;
        // System.out.println("moveLeft JButton has been clicked");
        // System.out.println(horizontal);
    } else {
        horizontal += MOVE;
        // System.out.println("moveRight button has been clicked");
        // System.out.println(horizontal);

    }
    repaint();
}

// draw ball

@Override
public void paintComponent(Graphics g) {

    final int DIAMETER = 100;
    final int VERTICAL = (getHeight() / 2) - (DIAMETER / 2);

    center = getWidth() / 2;
    horizontal = center - DIAMETER / 2;

    super.paintComponents(g);
    g.setColor(Color.ORANGE);
    g.fillOval(horizontal, VERTICAL, DIAMETER, DIAMETER); 
    g.setColor(Color.BLACK);
    g.drawOval(horizontal, VERTICAL, DIAMETER, DIAMETER);
    g.drawOval(horizontal + DIAMETER / 4, VERTICAL, DIAMETER / 2, DIAMETER);

    }

}

MoveBall类：

package test;

import javax.swing.*;

public class MoveBall extends JFrame {

public MoveBall() {

    // JFrame object

    JFrame frame = new JFrame();

    // JFrame properties

    frame.setSize(500, 500);
    frame.setLocationRelativeTo(null);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setTitle("Move ball");
    frame.add(new MoveBallPanel());
    frame.setVisible(true);

}

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

}

Answer 1

看看你的两段代码......

@Override
public void actionPerformed(ActionEvent e) {
    final int MOVE = 50;
    if (e.getSource() == moveLeft) {
        horizontal -= MOVE;
    } else {
        horizontal += MOVE;

    }
    repaint();
}

在actionPerformed方法中，您正在更新horizontal值，这听起来很合理，但在您的paintComponent方法中，您正在使用其他内容重新分配值，从而覆盖{ {1}}方法确实......

actionPerformed

首先看一下Performing Custom Painting和Painting in AWT and Swing，了解绘画如何在Swing中发挥作用。

你需要做的是创建某种标志，可用于告诉public void paintComponent(Graphics g) { //... horizontal = center - DIAMETER / 2; //... }方法将paintComponent初始化为默认位置，然后让程序更新那里...

绘画没有重新粉刷

1 个答案: