repaint() 突然不起作用

Question

我进行了大约 30 次不同的 google 搜索，但没有找到答案，所以我来到了这里。所以我试图在屏幕上左右移动播放器的矩形（黑色方块）。当我使用常规图形时它工作正常，但现在我使用 Graphics2D 时 repaint() 似乎什么都不做（即当你按下左右箭头键时，矩形不会移动）。

import java.util.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.JComponent;
import javax.swing.JFrame;

public class boxface extends JComponent implements KeyListener {

  private boxobj obj;

  private int x=0, y=650;

  public void keyPressed(KeyEvent e) {
    if(e.getKeyCode()== KeyEvent.VK_RIGHT)
      moveRight();
    else if(e.getKeyCode()== KeyEvent.VK_LEFT)
      moveLeft(); }
  public void keyReleased(KeyEvent e) {}
  public void keyTyped(KeyEvent e) {}

  Rectangle player = new Rectangle(x, y, 50, 50);
  Rectangle floor = new Rectangle(0, 700, 750, 700);

  public void paintComponent(Graphics g) {
    super.paintComponent(g);
    Graphics2D g2 = (Graphics2D) g;
    g.setColor(Color.GREEN);
    g2.fill(floor);
    g.setColor(Color.BLACK);
    g2.fill(player); }

  public void moveLeft() {
    if(x > 0) {
      x -= 50;
      repaint(); }}

  public void moveRight() {
    if(x < 700) {
      x += 50;
      repaint(); }}

  public boxface(){
    this.obj=new boxobj();
    addKeyListener(this);
    setFocusable(true);
    setFocusTraversalKeysEnabled(false); }

  public static void main(String[] args) {
    javax.swing.SwingUtilities.invokeLater(new Runnable() {
      public void run() {

        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setBounds(400, 200, 756, 779);
        f.setMinimumSize(new Dimension(756, 0));
        f.setResizable(false);
        f.getContentPane().add(new boxface());
        f.setVisible(true);

      }

    });

    final java.util.Timer tmr = new java.util.Timer();
    tmr.scheduleAtFixedRate(new TimerTask()
    {
      public void run()
      {
        System.out.println("A second has passed.");

        /* the idea is that I could make a square with random
         * dimensions (within a certain limit), so that every
         * time the timer loops, a new, random square is made.
         * I just can't seem to move the rectangles using
         * repaint(); because they're Graphics2D rectangles,
         * and I can't find a way around this.
         * 
         * An example of this can be shown if you run this
         * code; the "player" rectangle cannot be moved, even
         * though keylistener is picking up inputs and the
         * rectangle's co-ordinates are being changed. In
         * other words, repaint(); isn't doing anything. */



      }
    },0,1000);

  }//end main

}//end class

此外，"boxobj" class 现在只是一个空的 class。这是我计划放置随机矩形初始化的地方。我就放在这里方便复制粘贴。

public class boxobj {

}

Answer 1

问题是您正在更新 x 变量，但绘制了 player 对象。

当你构造player（通过Rectangle player = new Rectangle(x, y, 50, 50);）时，它会在执行该行时获取x值的副本。由于您同时声明和初始化，我们知道 x 为零，因此 player 将用 (0, 650, 50, 50).

实例化

稍后，用户按下右箭头键，您的事件侦听器将触发。这会将 x 增加到 50 并调用 repaint 但重要的是，根本不会更新 player 对象。当 paintComponent 方法被绘画系统调用时 player 仍然是 (0, 650, 50, 50).

本质上 x 和 y 记录了玩家的位置，但是您使用 player 对象来绘制玩家并且这些变量没有同步更新。

纠正这个问题的最好方法是将玩家的位置准确地存储在一个地方。您可以保留 x 和 y 并修改 paintComponent 方法以使用它们，或者您可以丢弃这两个变量并改为修改 player 对象（使用 player.setLocation).两种方法都行。

repaint() 突然不起作用

repaint() suddenly doesn't work

java

graphics2d