您好，感谢您阅读此问题。我是java程序的初学者，我试图用我现在已有的知识创建一个程序。我试图创建的程序是一个绘图程序，它基本上只允许您移动一个形状，并将形状绘制到框架上。我遇到的一个问题是，当我画它时不会留下痕迹。我认为它没有留下痕迹，因为我重写了paint方法，当我想要绘制一个新的时，它会清除我以前绘制的对象。但是当我删除覆盖它的代码并运行程序时，形状会留下一条痕迹，但框架顶部的按钮会搞得一团糟。
这是我的代码：
package MovingBlock;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.FlowLayout;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import javax.swing.*;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;
public class MovingBlockFrame extends JFrame implements KeyListener, ActionListener, ChangeListener{
FlowLayout flo = new FlowLayout(FlowLayout.LEADING, 10, 10);
JPanel buttonPanel = new JPanel();
JButton circle = new JButton("Circle");
JButton rectangle = new JButton("Rectangle");
JButton color = new JButton("Color");
JSlider speed = new JSlider(0, 100, 10);
Graphics2D test3;
int desiredWidth = 780;
int desiredHeight = 800;
MovingBlockCanvas background = new MovingBlockCanvas();
int paintSpeed = 10;
boolean diagonalKeysDown;
boolean diagonalKeysUp;
public MovingBlockFrame(){
setTitle("Painter");
buttonPanel.setBorder(BorderFactory.createLineBorder(Color.black));
setSize(desiredWidth, desiredHeight);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
KeyListener();
buttonPanel.setLayout(flo);
buttonPanel.add(circle);
buttonPanel.add(rectangle);
buttonPanel.add(color);
buttonPanel.add(speed);
background.desiredShape = "Circle";
background.addKeyListener(this);
add(background);
add(buttonPanel, BorderLayout.NORTH);
setVisible(true);
}
public static void main(String[] args){
MovingBlockFrame frame = new MovingBlockFrame();
frame.addKeyListener(frame);
}
public void keyPressed(KeyEvent input) {
int pressed = input.getKeyCode();
if(pressed == 83){
diagonalKeysDown = true;
background.xValue+= paintSpeed;
background.repaint();
}else if(pressed == 68 && !diagonalKeysDown){
background.yValue+=paintSpeed;
background.repaint();
}else if(pressed == 87 ){
diagonalKeysUp = true;
background.xValue-=paintSpeed;
background.repaint();
}else if(pressed == 65 ){
background.yValue-=paintSpeed;
background.repaint();
} if(diagonalKeysDown && pressed == 68){
background.yValue+=paintSpeed;
background.xValue+= paintSpeed;
background.repaint();
} if(diagonalKeysUp && pressed == 68){
background.yValue+=paintSpeed;
background.xValue-= paintSpeed;
background.repaint();
} if(diagonalKeysDown && pressed == 65){
background.yValue-=paintSpeed;
background.xValue+= paintSpeed;
background.repaint();
} if(diagonalKeysUp && pressed == 65){
background.yValue-=paintSpeed;
background.xValue-= paintSpeed;
background.repaint();
}
}
public void keyReleased(KeyEvent input) {
int released = input.getKeyCode();
if(released == 83){
diagonalKeysDown = false;
} if(released == 87){
diagonalKeysUp = false;
}
}
public void keyTyped(KeyEvent input) {
}
public void actionPerformed(ActionEvent event) {
String command = event.getActionCommand();
if(command.equals("Circle")){
background.desiredShape = "Circle";
background.repaint();
}else if (command.equals("Rectangle")){
background.desiredShape = "Rectangle";
background.repaint();
}else if(command.equals("Color")){
//ColorSliders test = new ColorSliders();
}
}
public void stateChanged(ChangeEvent event) {
JSlider source = (JSlider) event.getSource();
if(source.getValueIsAdjusting() != true){
paintSpeed = source.getValue();
}
}
public void KeyListener(){
buttonPanel.addKeyListener(this);
circle.addKeyListener(this);
rectangle.addKeyListener(this);
circle.addActionListener(this);
rectangle.addActionListener(this);
color.addKeyListener(this);
color.addActionListener(this);
speed.addKeyListener(this);
speed.addChangeListener(this);
}
}
然后有这个班：
package MovingBlock;
import java.awt.Graphics;
import javax.swing.JPanel;
import javax.swing.JPanel;
public class MovingBlockCanvas extends JPanel {
int xValue = 50;
int yValue = 50;
String desiredShape;
public MovingBlockCanvas(){
}
public void paint(Graphics render){
//super.paint(render);
render.setColor(ColorPanel.getColor2());
if(desiredShape == "Rectangle"){
render.fillRect(yValue, xValue, 50, 50);
}
if(desiredShape == "Circle"){
render.fillOval(yValue, xValue, 50, 50);
}
}
}
这是我到目前为止的代码。所以问题出在paint方法中，当我覆盖方法时，我不会为形状留下痕迹。如果你有任何编码技巧，我很乐意听到它们。提前谢谢。
答案 0 :(得分：1)
这是我学会修复此错误的原因。我只需创建一个新的缓冲图像，然后绘制到该图像，然后使用paintComponent方法重绘缓冲的图像。这是我使用更新的代码创建的类，使程序绘制并在形状后面留下痕迹，同时仍然覆盖paintComponenet方法。
public class MovingBlockCanvas extends JPanel {
int xValue = 50;
int yValue = 50;
int width = 10;
int height = 10;
String desiredShape;
BufferedImage drawing;
public MovingBlockCanvas(){
}
public void drawShapes(){
if(drawing == null){
createBufferedImage();
}
if(desiredShape.equals("Rectangle")){
Graphics2D g = drawing.createGraphics();
g.setColor(ColorPanel.getColor2());
g.fillRect(yValue, xValue, width, height);
g.dispose();
}
if(desiredShape.equals("Circle")){
Graphics2D g = drawing.createGraphics();
g.setColor(ColorPanel.getColor2());
g.fillOval(yValue, xValue, width, height);
g.dispose();
}
repaint();
}
public void createBufferedImage() {
BufferedImage buffer = new BufferedImage(getWidth(), getHeight(), BufferedImage.TYPE_INT_RGB);
Graphics2D g2d = buffer.createGraphics();
g2d.setColor(Color.white);
g2d.fillRect(0, 0, getWidth(), getHeight());
g2d.dispose();
drawing = buffer;
}
@Override
public void paintComponent(Graphics render){
super.paintComponent(render);
Graphics2D g = (Graphics2D) render.create();
if(drawing == null){
createBufferedImage();
}
g.drawImage(drawing, 0, 0, this);
g.dispose();
}
}
感谢所有帮助我学习这一切的人！