這個JPanel爲什麼不清除任何圖形？

Question

我試圖用給定的JTextField顯示100個字符串，一旦我按下繪圖按鈕，然後能夠按下旋轉按鈕時將它們全部旋轉90度。但是，當我旋轉時，來自較早的一些字符串仍然出現。但是，一旦弦向下指向，整個面板就會清除。爲什麼是這樣？

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

那麼它已經難比我的預期，但我認爲我得到了它的:-)

工作的第一個問題是你在的actionPerformed執行圖形操作（繪畫和轉換）。您必須在paintComponent中執行這些操作，因爲它是圖形環境自動執行的方法，無論何時需要繪製組件。

然後我不得不亂轉換一點點。我認爲問題在於你正在調用g2.setTransform（at）來應用新的座標變換。我讀過你不應該的文檔：「setTransform方法僅用於恢復原始的Graphics2D變換後渲染」

這是我出來。希望能幫助到你。

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(); 
    } 

}