java - 对象类未绘制到屏幕上

Question

我目前正在开发一个小型编码项目，但遇到了一个问题。我回顾了我过去的工作，我似乎无法弄清楚为什么这个程序不会调用paint方法。目前我只是想在框架上画一个圆圈。

以下内容为我尝试绘制的简单圆圈创建窗口和对象类。

public class Main {

public static void main(String[] args) {

    final int WIDTH = 700, HEIGHT = 900;

    JFrame frame = new JFrame("Physics Demo");
    JPanel content = new JPanel();

    content.setLayout(new GridLayout(1, 0, 0, 0));

    Character ball = new Character(WIDTH, HEIGHT);

    Timer changeFrame = new Timer (100, ball);

    frameSetup(frame, content, WIDTH, HEIGHT, ball, changeFrame);

}

public static void frameSetup(JFrame frame, JPanel content, int WIDTH, int HEIGHT, Character ball, Timer changeFrame){

    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    frame.setContentPane(content);

    content.add(ball);

    frame.addKeyListener(ball);

    frame.setPreferredSize(new Dimension(WIDTH, HEIGHT));

    frame.setResizable(false);
    frame.pack();
    frame.setLocationRelativeTo(null);

    frame.setVisible(true);
    changeFrame.start();

}

}

下面的类是对象类，当我运行程序时，我从控制台得到响应。角色触发一次(理应如此)，并且 actionPreformed 方法与计时器一起循环运行。由于某种原因它不运行绘图类。

public class Character extends JPanel implements ActionListener, KeyListener{
/* Identify the Objects values and physics,
 * Characters weight, size and properties are below.
 * 
 */
private static final long serialVersionUID = 1L;

final int characterRadius = 30;

final double characterWeight = 0.5;

int characterY, characterX;

boolean bouncy;

public Character(int WIDTH, int HEIGHT){

    System.out.println("Character called upon... " + WIDTH);

}

public void characterObject(Graphics g, int WIDTH, int HEIGHT){

    super.paint(g);

    System.out.println("characterObject graphics called upon... " + WIDTH);

    g.setColor(Color.BLUE);
    g.fillOval(350, 450, characterRadius, characterRadius);

}

/*
 * Ball does not have any player interactions
 */

@Override
public void keyPressed(KeyEvent buttonPressed) {


}

@Override
public void keyReleased(KeyEvent arg0) {

}

@Override
public void keyTyped(KeyEvent arg0) {


}

//******************************************

@Override
public void actionPerformed(ActionEvent arg0) {

    System.out.println("actionPreformed called upon...");

    repaint();

}

}

我已经进行了一段时间的试验和错误，但我似乎无法弄清楚，所以我将此作为最后的手段。

如果需要，我可以提供更多信息。

Answer 1

为什么要从 characterObject 调用 super.paint？这不是定制绘画的工作原理。您无法控制绘制过程，API 可以控制

您需要重写当 API 希望重新绘制组件时调用的方法之一。作为一般建议，例如，这将是 paintComponent 方法

public class Character extends JPanel implements ActionListener, KeyListener {

    /* Identify the Objects values and physics,
     * Characters weight, size and properties are below.
     * 
     */
    private static final long serialVersionUID = 1L;

    final int characterRadius = 30;

    final double characterWeight = 0.5;

    int characterY, characterX;

    boolean bouncy;

    public Character(int WIDTH, int HEIGHT) {

        System.out.println("Character called upon... " + WIDTH);

    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g); //To change body of generated methods, choose Tools | Templates.
        System.out.println("characterObject graphics called upon... " + WIDTH);

        g.setColor(Color.BLUE);
        g.fillOval(350, 450, characterRadius, characterRadius);

    }

    /*
     * Ball does not have any player interactions
     */
    @Override
    public void keyPressed(KeyEvent buttonPressed) {

    }

    @Override
    public void keyReleased(KeyEvent arg0) {

    }

    @Override
    public void keyTyped(KeyEvent arg0) {

    }

    //******************************************
    @Override
    public void actionPerformed(ActionEvent arg0) {

        System.out.println("actionPreformed called upon...");

        repaint();

    }
}

我建议阅读 Performing Custom Painting和 Painting in Swing有关 Swing 中绘画实际工作原理的更多详细信息。

我还建议您查看 How to use Key Bindings作为 KeyListener 的替代品，这将解决您下一个明显的问题

您可能还想阅读Java Coding Conventions ，这会让其他人更容易阅读你的代码，也让你更容易阅读别人的代码。

您将宽度和高度传递给Character构造函数，但忽略它们，我建议您去需要将这些值分配给实例字段并在 paintComponent 方法中使用它们