graphics.setColor（color）;不工作

Question

我想創建一個小小的塔防遊戲顏色但顏色不工作這裏是我如何繪製rects做圖形。

public static void fill(GridLocation loc, Color c){ 
    Main.frame.getGraphics().setColor(c); 
    Main.frame.getGraphics().fillRect(loc.toFrameLocation().x, loc.toFrameLocation().y, 20, 20); 
    Main.frame.getGraphics().dispose(); 
} 

和，這是我如何調用/創建的JFrame

public static void main(String[] args) { 
    frame = new JFrame("Tower defense"); 
    frame.setSize(1000, 700); 
    frame.setVisible(true); 
    frame.setLayout(null); 
    frame.setLocationRelativeTo(null); 
    frame.setResizable(false); 
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
    while (frame.isVisible()){ 
     Grid.fill(new GridLocation(1,1), new Color(1F,0F,0F)); 
     Grid.fill(new GridLocation(2,1), Color.gray); 
     Grid.drawGrid(); 
     Grid.fill(new GridLocation(3,1), Color.green); 
    } 
} 

我的問題：矩形總是黑色？

Answer 1

請注意，如果您使用組件上的getGraphics()來獲取Graphics上下文，則獲得的圖形將不會持續。例如，在下面的代碼中，您會看到如果按下該按鈕，則會出現一個藍色矩形，但如果GUI最小化並稍後調整大小，則該矩形會消失。

另外，按我的意見：在JPanel的paintComponent方法裏面

1. 平局。
2. 使用Swing Timer不是一個（true）循環。
3. 在該Timer中，更改圖形JPanel的狀態（更改其字段），然後調用repaint（）。
4. 然後讓paintComponent方法使用這些字段來告訴它如何繪製。
5. 不要忘記在你的覆蓋範圍內調用super的繪畫方法。

例如：

import java.awt.Color; 
import java.awt.Dimension; 
import java.awt.Graphics; 
import java.awt.event.ActionEvent; 
import javax.swing.*; 

@SuppressWarnings("serial") 
public class UnstableStableGraphics extends JPanel { 
    private static final int PREF_W = 800; 
    private static final int PREF_H = 400; 
    private static final int GAP = 20; 

    public UnstableStableGraphics() { 
     add(new JButton(new DrawBlueRectAction())); 
    } 

    @Override 
    protected void paintComponent(Graphics g) { 
     super.paintComponent(g); 
     g.setColor(Color.RED); 
     int w = PREF_W/2 - 2 * GAP; 
     int h = PREF_H - 2 * GAP; 
     g.fillRect(GAP, GAP, w, h);  
    } 

    @Override 
    public Dimension getPreferredSize() { 
     return new Dimension(PREF_W, PREF_H); 
    } 

    private class DrawBlueRectAction extends AbstractAction { 
     public DrawBlueRectAction() { 
      super("Draw Unstable Blue Rectangle"); 
     } 

     @Override 
     public void actionPerformed(ActionEvent arg0) { 
      Graphics g = getGraphics(); 
      g.setColor(Color.BLUE); 
      int x = PREF_W/2 + GAP; 
      int w = PREF_W/2 - 2 * GAP; 
      int h = PREF_H - 2 * GAP; 
      g.fillRect(x, GAP, w, h); 
      g.dispose(); 
     } 
    } 

    public static void main(String[] args) { 
     SwingUtilities.invokeLater(() -> createAndShowGui()); 
    } 

    private static void createAndShowGui() { 
     UnstableStableGraphics mainPanel = new UnstableStableGraphics(); 
     JFrame frame = new JFrame("UnstableStableGraphics"); 
     frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE); 
     frame.add(mainPanel); 
     frame.pack(); 
     frame.setLocationByPlatform(true); 
     frame.setVisible(true); 
    } 
} 

說了這麼多，這是完全正常的使用要求一個BufferedImage通過getGraphics()獲得Graphics對象（只要你處理圖形的完成時對象，以完成後節省資源），然後將該圖像顯示在paintComponent方法中，通常作爲背景圖像顯示。但是，通常我會在BufferedImage上調用createGraphics()，因爲它返回的是更強大的Graphics2D對象，而不是Graphics對象。

例如，包括使用的背景圖像，子畫面圖像和一個Swing定時器：

import java.awt.Color; 
import java.awt.Dimension; 
import java.awt.Graphics; 
import java.awt.Graphics2D; 
import java.awt.Image; 
import java.awt.RenderingHints; 
import java.awt.event.ActionEvent; 
import java.awt.event.ActionListener; 
import java.awt.image.BufferedImage; 

import javax.swing.*; 

@SuppressWarnings("serial") 
public class BackgroundExample extends JPanel { 
    private static final int PREF_W = 600; 
    private static final int PREF_H = PREF_W; 
    private static final int SPRITE_W = 20; 
    private static final Color SPRITE_COLOR = Color.RED; 
    private static final int TIMER_DELAY = 20; 
    private Image background = null; 
    private Image sprite = null; 
    private int spriteX = 0; 
    private int spriteY = 0; 

    public BackgroundExample() { 
     background = createBackground(); 
     sprite = createSprite(); 

     new Timer(TIMER_DELAY, new TimerListener()).start(); 
    } 

    private Image createSprite() { 
     BufferedImage img = new BufferedImage(SPRITE_W, SPRITE_W, BufferedImage.TYPE_INT_ARGB); 
     Graphics2D g2 = img.createGraphics(); 
     g2.setColor(SPRITE_COLOR); 
     g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); 
     int x = 1; 
     int y = 1; 
     int width = SPRITE_W -2; 
     int height = SPRITE_W - 2; 
     g2.fillOval(x, y, width, height); 
     g2.dispose(); 
     return img; 
    } 

    private Image createBackground() { 
     BufferedImage img = new BufferedImage(PREF_W, PREF_H, BufferedImage.TYPE_INT_ARGB); 
     Graphics2D g2 = img.createGraphics(); 
     g2.setColor(Color.GREEN); 
     g2.fillRect(0, 0, PREF_W, PREF_H); 
     g2.setColor(Color.GRAY); 
     int x = 0; 
     int y = 0; 
     g2.fillRect(x, y, 2 * SPRITE_W, 2 * SPRITE_W); 
     x = PREF_W - 2 * SPRITE_W; 
     g2.fillRect(x, y, 2 * SPRITE_W, 2 * SPRITE_W); 
     y = PREF_H - 2 * SPRITE_W; 
     g2.fillRect(x, y, 2 * SPRITE_W, 2 * SPRITE_W); 
     x = 0; 
     g2.fillRect(x, y, 2 * SPRITE_W, 2 * SPRITE_W); 
     g2.dispose(); 
     return img; 
    } 

    @Override 
    protected void paintComponent(Graphics g) { 
     super.paintComponent(g); 
     if (background != null) { 
      g.drawImage(background, 0, 0, this); 
     } 
     if (sprite != null) { 
      g.drawImage(sprite, spriteX, spriteY, this); 
     } 
    } 

    @Override 
    public Dimension getPreferredSize() { 
     if (isPreferredSizeSet()) { 
      return super.getPreferredSize(); 
     } else { 
      return new Dimension(PREF_W, PREF_H); 
     } 
    } 

    private class TimerListener implements ActionListener { 
     @Override 
     public void actionPerformed(ActionEvent e) { 
      spriteX++; 
      spriteY++; 
      repaint(); 
     } 
    } 

    public static void main(String[] args) { 
     SwingUtilities.invokeLater(() -> createAndShowGui()); 
    } 

    private static void createAndShowGui() { 
     BackgroundExample mainPanel = new BackgroundExample(); 
     JFrame frame = new JFrame("BackgroundExample"); 
     frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     frame.add(mainPanel); 
     frame.pack(); 
     frame.setLocationRelativeTo(null); 
     frame.setVisible(true); 
    } 
}