如何從Java中的其他類訪問paintComponent（）？

Question

所以，我有我的主要類延伸JFrame，我有第二課延伸JPanel允許paintComponent借鑑JPanel。但是，如何訪問新課程以繪製JPanel？

這裏是我的代碼：

import java.awt.*; 
import java.awt.event.*; 
import javax.swing.*; 
import javax.swing.border.*; 

public class MTGSAMPServerReference extends JFrame implements ActionListener { 
    public static Toolkit tk = Toolkit.getDefaultToolkit(); 
    static int ScrnWidth = ((int) tk.getScreenSize().getWidth()); 
    static int ScrnHeight = ((int) tk.getScreenSize().getHeight()); 
    private static final long serialVersionUID = 1L; 
    private static JList list1; 
    private static JButton next; 
    private static JPanel bg = new JPanel(); 

    public MTGSAMPServerReference() { 
     // set flow layout for the frame 
     this.getContentPane().setLayout(new FlowLayout(FlowLayout.LEADING)); 
     Object[]mainData = {"Vehicles", "Bikes/Bicycles", "Boats", "Houses", "Businesses", "Objects", "Jobs", "Ranks", "Licenses", "VIP"}; 
     JPanel controls = new JPanel(new BorderLayout(5,5)); 
     list1 = new JList<Object>(mainData); 
     list1.setVisibleRowCount(10); 
     next = new JButton("Next"); 
     next.addActionListener(this); 
     controls.add(new JScrollPane(list1)); 
     controls.add(next, BorderLayout.PAGE_END); 
     controls.setBorder(new EmptyBorder(25,25,0,0)); 
     add(controls); 
    } 

    @Override 
    public void actionPerformed(ActionEvent e) { 
     if (e.getActionCommand().equals("Next")) { 
      int index = list1.getSelectedIndex(); 
      System.out.println("Index Selected: " + index); 
      String s = (String) list1.getSelectedValue(); 
      System.out.println("Value Selected: " + s); 
     } 
    } 

    public void createAndShowGUI() { 
     //Create and set up the window. 
     JFrame f = new MTGSAMPServerReference(); 
     //Display the window. 
     f.pack(); 
     f.setVisible(true); 
     f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 

     f.setSize(1200, 800); 
     f.setLocationRelativeTo(null); 
     list1.setSize(250, 250); 
     list1.setLocation(0, 0); 
     next.setSize(75, 25); 
     next.setLocation(251, 276); 
     MTGSAMPServerReference.this.repaint(); 
    } 

    public static void main(String[] args) { 
     javax.swing.SwingUtilities.invokeLater(new Runnable() { 
      public void run() { 
      MTGSAMPServerReference gui = new MTGSAMPServerReference(); 
      gui.createAndShowGUI(); 
      } 
     }); 
    } 
} 

class drawOnPanel extends JPanel { 
    protected void paintComponent(Graphics g) { 
     super.paintComponent(g); 
     Graphics2D g2 = (Graphics2D)g; 
     g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); 
     g2.drawRect(0, 0, 50, 50); 
    } 
} 

任何想法？

在此先感謝！

Answer 1

您只需像添加任何其他組件一樣添加面板即可。當需要重繪時，調用paintComponent方法。

Answer 2

您沒有將drawOnPanel類添加到框架的容器中。加入這一行：

add(new drawOnPanel()); 

---

其他注意事項：

1. 裏面createAndShowGUI()，你從JFrame已經擴展分類，也沒有必要創建另一個JFrame對象，將其更改爲：

   public void createAndShowGUI() { 
       //Create and set up the window. 
       //JFrame f = new MTGSAMPServerReference(); 
       //Display the window. 
   
       setVisible(true); 
       setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
       setSize(1200, 800); 
       setLocationRelativeTo(null); 
       list1.setSize(250, 250); 
       list1.setLocation(0, 0); 
       next.setSize(75, 25); 
       next.setLocation(251, 276); 
       repaint(); 
       pack(); 
   } 
   

2. 重新繪製後，選擇pack()方法，以適合組件的尺寸，就像我在上面所做的那樣。

@ knorberg的評論：在哪裏以及如何繪製我的矩形？

繪圖是好的，只是覆蓋getPreferredSize()方法drawOnPanel類中：

class drawOnPanel extends JPanel { 
    @Override 
    protected void paintComponent(Graphics g) { 
     super.paintComponent(g); 
     Graphics2D g2 = (Graphics2D)g; 
     g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); 
     g2.drawRect(0, 0, 50, 50); 
    } 
    @Override 
    public Dimension getPreferredSize(){ 
    return new Dimension(200,200); 
    } 
}