Question

我遇到了问题，我希望绘制一个正方形（苍蝇）并重新绘制以显示运动。按下按钮时此代码很好，苍蝇会“移动”，但旧方块不会删除。我已经尝试了enviromentPanel.repaint（）updateui（）和removeall（），我无法让它工作，如果我使用其中任何一个，那么没有任何形状出现，我得到一个空白的屏幕。

import java.util.Random;


public class Fly implements Runnable{
private int xPosition;
private int yPosition;
private boolean eaten;

public Fly(){
    Random randomGenerator = new Random();
    xPosition = randomGenerator.nextInt(690) + 10;
    yPosition = randomGenerator.nextInt(690) + 10;
    eaten = false;
}

public int getxPosition() {
    return xPosition;
}

public void setxPosition(int xPosition) {
    this.xPosition = xPosition;
}

public int getyPosition() {
    return yPosition;
}

public void setyPosition(int yPosition) {
    this.yPosition = yPosition;
}

public boolean isEaten() {
    return eaten;
}

public void setEaten(boolean eaten) {
    this.eaten = eaten;
}

public void move(){
      Random randomGenerator = new Random();

        int xChange = -10 + randomGenerator.nextInt(20);
        int yChange = -10 + randomGenerator.nextInt(20);
        xPosition = xPosition + xChange;
        yPosition = yPosition + yChange;
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        move();

}

@Override
public String toString() {
    return "Fly [xPosition=" + xPosition + ", yPosition=" + yPosition
            + ", eaten=" + eaten + "]";
}

@Override
public void run() {
    move();
}


}

import java.awt.Color;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.Panel;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import javax.swing.*;
import java.awt.*;
import javax.imageio.ImageIO;

public class Enviroment2 implements Runnable,ActionListener{ 
private JFrame frame;
private JPanel enviromentPanel,totalGUI,enviromentButtonPanel;
private JButton newFrogButton, resetButton, hungryButton;
private JTextField enterName;
private JLabel hungryLabel;
private ArrayList<Frog> frogs;
private ArrayList<Fly> flys;



public Enviroment2(){
totalGUI = new JPanel();
flys = new ArrayList<Fly>();
frogs = new ArrayList<Frog>();
enviromentPanel = new JPanel();
enviromentButtonPanel = new JPanel();
newFrogButton = new JButton("New Frog");
enterName = new JTextField("Enter name");

hungryButton = new JButton("Hungry!");

resetButton = new JButton("Reset");
frame = new JFrame("[=] Hungry Cyber Pet [=]");
JFrame.setDefaultLookAndFeelDecorated(true);

frame.setContentPane(runEnviroment());

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(740, 800);
frame.setVisible(true);



}



public JPanel runEnviroment(){

totalGUI.setLayout(null);

enviromentPanel.setLayout(null);
enviromentPanel.setLocation(10, 10);
enviromentPanel.setSize(700, 700);
enviromentPanel.setBackground(Color.WHITE);
totalGUI.add(enviromentPanel);


FlowLayout experimentLayout = new FlowLayout();
enviromentButtonPanel.setLayout(experimentLayout);
enviromentButtonPanel.setLocation(10, 710);
enviromentButtonPanel.setSize(700, 50);
totalGUI.add(enviromentButtonPanel);

newFrogButton.setLocation(0, 0);
newFrogButton.setSize(120, 30);
newFrogButton.addActionListener(this);
enviromentButtonPanel.add(newFrogButton);

enterName.setLocation(140,0);
enterName.setSize(120,30);
enviromentButtonPanel.add(enterName);

hungryButton.setLocation(280, 0);
hungryButton.setSize(120, 30);
hungryButton.addActionListener(this);
enviromentButtonPanel.add(hungryButton);

resetButton.setLocation(420, 0);
resetButton.setSize(120, 30);
resetButton.addActionListener(this);
enviromentButtonPanel.add(resetButton);


totalGUI.setOpaque(true);

return totalGUI;
}


public void draw(){     

Graphics paper = enviromentPanel.getGraphics();

for (int i = 0; i <= flys.size()-1; i++){
    System.out.println("hi");
    paper.setColor(Color.BLACK);

    paper.fillRect(flys.get(i).getxPosition(), flys.get(i).getyPosition(), 10,      10);




}
try {
    Thread.sleep(1000);
} catch (InterruptedException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
}

draw();

}

public void actionPerformed(ActionEvent e) {
 if(e.getSource() == newFrogButton){
     Frog frog = new Frog(enterName.getText());
     frogs.add(frog);
     Fly fly = new Fly();
     Thread t = new Thread(fly);
     t.start();
     flys.add(fly);
     showFlys();

  }
  else if(e.getSource() == hungryButton){
  }
  else if(e.getSource() == resetButton){
      frogs.clear();
      flys.clear();
      System.out.println(frogs);
      System.out.println(flys);


  }
}


public void showFlys(){
for (int i = 0; i <= flys.size()-1; i++){
    System.out.println(flys.get(i));
}

}



@Override
public void run() {
draw(); 
}



}

Answer 1

这个Graphics paper = enviromentPanel.getGraphics()是问题的开始，这不是自定义绘画的完成方式。

getGraphics返回上一个绘制周期中使用的图形上下文，最好是快照，最差的可能是null。

您永远不应该保留对您未创建的任何Graphics上下文的引用。他们可以改变并且在它上面绘画可以产生意想不到的效果。

相反，您应该覆盖paintComponent方法（可能在environmentPanel中）并在其中执行所有自定义绘制。

你的第二个问题是你违反了Swing的线程规则 - 你不应该在EDT之外的任何线程中创建或修改任何UI组件

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