java对象类未绘制到屏幕

1 周，5 日 Questions & Answers 28

我目前正在做一个小的编码项目，我遇到了一个问题。我回顾了我过去的工作，我似乎不明白为什么这个程序不调用绘画方法。目前我只是想在画面上画一个圆圈

下面为我试图绘制的简单圆创建窗口和对象类

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，我从控制台得到一个响应。字符触发一次（应该触发），actionPreformed方法在带有计时器的循环上运行。出于某种原因，它不运行paint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();

}

}

我已经做了一段时间的尝试和错误现在，我似乎无法找出它，所以我用这个作为最后的手段

如果需要，我可以提供更多信息

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(); } }

共 (2) 个答案

# 1 楼答案

你为什么从characterObject打电话给super.paint？这不是定制绘画的工作方式。你不能控制绘画过程，API可以

当API希望重新绘制组件时，需要重写调用的方法之一。例如，作为一般性建议，这将是paintComponent方法

我建议大家阅读一下Performing Custom Painting和Painting in Swing，了解更多关于绘画如何在摇摆中实际工作的细节

我还建议大家看看How to use Key Bindings作为KeyListener的替代品，这将解决下一个明显的问题

您可能还想阅读Java Coding Conventions，这将使其他人更容易阅读您的代码，您也更容易阅读其他人的代码

您正在将width和height传递给Character构造函数，但忽略了它们，我建议您需要将这些值分配给实例字段，并在paintComponent方法中使用它们

# 2 楼答案
你不应该直接给油漆打电话。只要需要重新绘制，就会从框架中调用它。要强制重新绘制，只需调用“repaint（）”

如果从计时器调用，可能需要将调用放入EDT，这意味着EventDispatchThread：
```
EventQueue.invokeLater(new Runnable()
{
  @Override
  public void run()
  {
    ball.repaint();
  }
});
```
哦，你真的应该覆盖绘画方法：
```
@Override
public void paint(Graphics g)
{
  super.paint(g);
  g.setColor(Color.BLUE);
  g.fillOval(350, 450, characterRadius, characterRadius);
}
```

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java对象类未绘制到屏幕

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# 2 楼答案