为什么这个jpanel不会清除任何图形

Question

一旦我按下绘制按钮，我正在尝试使用给定的JTEXTFIELD显示100个字符串，然后在按下旋转按钮时能够将它们全部90度旋转。但是，当我旋转时，一些早期的字符串仍然出现。但是随后整个面板一旦字符串向下指向，整个面板就会清除。为什么这是？

import java.awt.Color;
import java.awt.Component;
import java.awt.FlowLayout;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridLayout;
import java.awt.RenderingHints;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.geom.AffineTransform;
import java.util.ArrayList;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingConstants;
public class RotateAndDraw extends JFrame implements ActionListener{
    // Declare all member variables
    private JFrame window;
    private JButton drawButton;
    private JButton rotateButton;
    JTextField userInput = new JTextField("Enter text here");
    private static JPanel p3 = new JPanel(); // Drawing surface
    private static Graphics g = p3.getGraphics(); // Graphics context
    private static int[] xArray = new int[100];
    private static int[] yArray = new int[100];
    private static int[] fontArray = new int[100];
    private static float[] colorArray = new float[100];
    private static int rotateCount = 0;
    private static int theta;
    public RotateAndDraw(){
        // Declare all components
        window = new JFrame("Rotate and Draw");
        drawButton = new JButton("Draw");
        rotateButton = new JButton("Rotate");
        drawButton.addActionListener(this);
        rotateButton.addActionListener(this);
        JPanel drawingSurface = new JPanel();
        JLabel userInputLabel = new JLabel("Text:         ");
        // Create some containers
        JPanel content = new JPanel();
        content.setLayout(new GridLayout(3, 1));
        JPanel p1 = new JPanel();
        p1.setLayout(new GridLayout(1, 2));
        p1.add(drawButton);
        p1.add(rotateButton);
        JPanel p2 = new JPanel();
        p2.setLayout(new GridLayout(1, 3));
        userInputLabel.setHorizontalAlignment(SwingConstants.RIGHT);
        p2.add(userInputLabel);
        p2.add(userInput);
        JLabel nullLabel = new JLabel("");
        p2.add(nullLabel);
        p3.setBackground(Color.BLACK);
        content.add(p1);
        content.add(p2);
        content.add(p3);
        window.add(content);
    }
    public void run(){
        window.setLocation(100, 100);
        window.setSize(10000, 10000);
        window.setDefaultCloseOperation(EXIT_ON_CLOSE);
        window.setVisible(true);
    }
    private void paintComponent(Graphics g){
        // TODO Auto-generated method stub
        super.paintComponents(g);
   }
    @Override
    public void actionPerformed(ActionEvent e) {
        // TODO Auto-generated method stub
        super.paintComponents(g);
        Graphics2D g2 = ( Graphics2D )g;
        String message = userInput.getText();
        Font font1, font2, font3, font4, font5;  // The five fonts.
        font1 = new Font("Serif", Font.BOLD, 14);
        font2 = new Font("SansSerif", Font.BOLD + Font.ITALIC, 24);
        font3 = new Font("Monospaced", Font.PLAIN, 30);
        font4 = new Font("Dialog", Font.PLAIN, 36);
        font5 = new Font("Serif", Font.ITALIC, 48);
        if(e.getSource() == drawButton){
            g = p3.getGraphics();
            g.setColor(Color.BLACK);
            g.fillRect(0, 0, p3.getWidth(), p3.getHeight());
            rotateCount = 0;
            int width = p3.getWidth();
            int height = p3.getHeight();
            for (int i = 0; i < 100; i++) {
                int fontNum = (int)(5*Math.random()) + 1;
                fontArray[i] = fontNum;
                switch (fontNum) {
                case 1:
                    g.setFont(font1);
                    break;
                case 2:
                    g.setFont(font2);
                    break;
                case 3:
                    g.setFont(font3);
                    break;
                case 4:
                    g.setFont(font4);
                    break;
                case 5:
                    g.setFont(font5);
                    break;
                } // end switch

                float hue = (float)Math.random();
                colorArray[i] = hue;
                g.setColor( Color.getHSBColor(hue, 1.0F, 1.0F) );

                int x,y;
                x = (int)(Math.random()*(width));
                y = (int)(Math.random()*(height));
                xArray[i] = x;
                yArray[i] = y;
                // Draw the message.
                g.drawString(message,x,y);
            } // end for
        }// end if
        if(e.getSource() == rotateButton){
            super.paintComponents(g2);
            g2.setColor(Color.BLACK);
            g2.fillRect(0, 0, p3.getWidth(), p3.getHeight());
            rotateCount++;
            if(rotateCount == 4){
                rotateCount = 0;
            }
            switch(rotateCount){
            case 0:
                theta = 0;
                break;
            case 1:
                theta = 90;
                break;
            case 2:
                theta = 180;
                break;
            case 3:
                theta = 270;
                break;
            }
            for(int i = 0; i < 100; i++){
                switch(fontArray[i]){
                case 1:
                    g2.setFont(font1);
                    break;
                case 2:
                    g2.setFont(font2);
                    break;
                case 3:
                    g2.setFont(font3);
                    break;
                case 4:
                    g2.setFont(font4);
                    break;
                case 5:
                    g2.setFont(font5);
                    break;
                } // end switch 
            g2.setColor( Color.getHSBColor(colorArray[i], 1.0F, 1.0F) );
            AffineTransform at = new AffineTransform(); 
            at.rotate(Math.toRadians(theta), xArray[i], yArray[i]);
            g2.setTransform(at); 
            g2.drawString(message, xArray[i], yArray[i]);
            g2.transform(new AffineTransform());
            }// end for
        }
    }
}

Answer 1

好吧，它比我预期的要难，但我认为我可以工作： - (

第一个问题是您在Action Performed中执行图形操作(绘图和转换(。您必须在PaintComponent中执行这些操作，因为这是图形环境需要在需要绘制组件时自动执行的方法。

然后，我不得不稍微解决转变。我认为问题是您打电话给g2.settransform(AT(应用新的坐标变换。我在文档上阅读了您不应该的文档：" setTransform方法仅用于恢复原始graphics2d transfor，"

">

这是我提出的。希望它有帮助。

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.geom.AffineTransform;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingConstants;
class Tag {
    private int     x;
    private int     y;
    private int     font;
    private float   color;
    private String  message;
    public Tag(String message, int x, int y, int font, float color) {
        this.message = message;
        this.x = x;
        this.y = y;
        this.font = font;
        this.color = color;
    }
    public String getMessage() {
        return message;
    }
    public int getX() {
        return x;
    }
    public int getY() {
        return y;
    }
    public int getFont() {
        return font;
    }
    public float getColor() {
        return color;
    }
}
class Board extends JPanel {
    private Font[]  font    = new Font[5];
    private Tag[]   tags;
    private int     theta;
    public Board() {
        font[0] = new Font("Serif", Font.BOLD, 14);
        font[1] = new Font("SansSerif", Font.BOLD + Font.ITALIC, 24);
        font[2] = new Font("Monospaced", Font.PLAIN, 30);
        font[3] = new Font("Dialog", Font.PLAIN, 36);
        font[4] = new Font("Serif", Font.ITALIC, 48);
    }
    public void setTags(Tag[] tags) {
        this.tags = tags;
    }
    public void updateBoard(int theta) {
        this.theta = theta;
    }
    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D) g;
        g2.setColor(Color.BLACK);
        g2.fillRect(0, 0, getWidth(), getHeight());
        if (tags != null) {
            AffineTransform at = new AffineTransform();
            for (Tag tag : tags) {
                g2.setFont(font[tag.getFont()]);
                g2.setColor(Color.getHSBColor(tag.getColor(), 1.0F, 1.0F));
                at = new AffineTransform();
                at.translate(tag.getX(), tag.getY());
                g2.transform(at);
                at = new AffineTransform();
                at.rotate(Math.toRadians(theta));
                g2.transform(at);
                g2.drawString(tag.getMessage(), 0, 0);
                at = new AffineTransform();
                at.rotate(-Math.toRadians(theta));
                g2.transform(at);
                at = new AffineTransform();
                at.translate(-tag.getX(), -tag.getY());
                g2.transform(at);
            }// end for
        }
    }
}
public class RotateAndDraw extends JFrame implements ActionListener {
    // Declare all member variables
    private JFrame  window;
    private JButton drawButton;
    private JButton rotateButton;
    JTextField      userInput   = new JTextField("Enter text here");
    private Board   board       = new Board();  // Drawing surface
    private int     rotateCount = 0;
    public RotateAndDraw() {
        // Declare all components
        window = new JFrame("Rotate and Draw");
        drawButton = new JButton("Draw");
        rotateButton = new JButton("Rotate");
        drawButton.addActionListener(this);
        rotateButton.addActionListener(this);
        JLabel userInputLabel = new JLabel("Text:         ");
        // Create some containers
        JPanel content = new JPanel();
        content.setLayout(new GridLayout(3, 1));
        JPanel p1 = new JPanel();
        p1.setLayout(new GridLayout(1, 2));
        p1.add(drawButton);
        p1.add(rotateButton);
        JPanel p2 = new JPanel();
        p2.setLayout(new GridLayout(1, 3));
        userInputLabel.setHorizontalAlignment(SwingConstants.RIGHT);
        p2.add(userInputLabel);
        p2.add(userInput);
        JLabel nullLabel = new JLabel("");
        p2.add(nullLabel);
        board.setBackground(Color.BLACK);
        content.add(p1);
        content.add(p2);
        content.add(board);
        window.add(content);
    }
    public void run() {
        window.setLocation(100, 100);
        window.setSize(400, 400);
        window.setDefaultCloseOperation(EXIT_ON_CLOSE);
        window.setVisible(true);
    }
    @Override
    public void actionPerformed(ActionEvent e) {
        String message = userInput.getText();
        if (e.getSource() == drawButton) {
            rotateCount = 0;
            int width = board.getWidth();
            int height = board.getHeight();
            Tag[] tags = new Tag[100];
            for (int i = 0; i < tags.length; i++) {
                int fontNum = (int) (5 * Math.random());
                float hue = (float) Math.random();
                int x = (int) (Math.random() * width);
                int y = (int) (Math.random() * height);
                tags[i] = new Tag(message, x, y, fontNum, hue);
            } // end for
            board.setTags(tags);
        }// end if
        if (e.getSource() == rotateButton) {
            rotateCount = (rotateCount + 1) % 4;
        }
        board.updateBoard(90 * rotateCount);
        board.repaint();
    }
    public static void main(String[] args) {
        RotateAndDraw rad = new RotateAndDraw();
        rad.run();
    }
}