Java的繪畫工作不

Question

所以我有這樣的代碼：

package tictactoe; 

import java.awt.Graphics; 
import java.awt.Graphics2D; 
import javax.swing.JFrame; 
import javax.swing.JPanel; 

public class TicTacToe extends JFrame { 

public static void main(String[] args) { 
    JFrame masterFrame = new JFrame("TicTacToe"); 
    JPanel drawingPanel = new JPanel(); 
    GameBoard theGame = new GameBoard(); 

    masterFrame.add(drawingPanel); 
    masterFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
    masterFrame.setSize(504, 504); 
    masterFrame.setResizable(false); 
    masterFrame.setLocationRelativeTo(null); 
    masterFrame.setVisible(true); 
} //End of Main method 


@Override 
public void paint (Graphics g) { 
    Graphics2D g2 = (Graphics2D) g; 
    //Drawing the GridLines 
    g2.drawLine(168, 0, 168, 500); 
    g2.drawLine(336, 0, 336, 500); 
    g2.drawLine(0, 168, 500, 168); 
    g2.drawLine(0, 336, 500, 336); 
} //End of Paint Method 
} //End of TicTacToe Class  

我想它做的是畫4條線到我的井字時尚的JFrame，但JFrame中仍爲空白。爲什麼是這樣？我的代碼有什麼問題，我應該如何解決它？

Answer 1

假如你實際創建的TicTacToe一個實例，而不是JFrame，你DrawingPane可能會被畫了/覆蓋什麼都你的框架是畫通過它paint方法。

// Create an instance of TicTacToe instead of JFrame... 
//JFrame masterFrame = new JFrame("TicTacToe"); 
TicTacToe masterFrame = new TicTacToe(); 

子組件可以在沒有通知或要求它被塗父容器，這意味着子組件實際上會掩蓋什麼先前已經由幀畫來畫，這可能會產生一些非常奇怪的結果，因爲不同部分得到更新

A JFrame包含許多子組件，包括JRootPane和contentPane，您將自己的組件放在其上。

在你的情況下更好的解決辦法可能是使用你的DrawingPane和定製它的paintComponent呈現網格

更多細節

例如見Painting in AWT and Swing和Performing Custom Painting ...

import java.awt.Dimension; 
import java.awt.EventQueue; 
import java.awt.Graphics; 
import java.awt.Graphics2D; 
import javax.swing.JFrame; 
import javax.swing.JPanel; 
import javax.swing.UIManager; 
import javax.swing.UnsupportedLookAndFeelException; 

public class TicTacToe { 

    public static void main(String[] args) { 
     new TicTacToe(); 
    } //End of Main method 

    public TicTacToe() { 
     EventQueue.invokeLater(new Runnable() { 
      @Override 
      public void run() { 
       try { 
        UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName()); 
       } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) { 
        ex.printStackTrace(); 
       } 

       JFrame frame = new JFrame("Tic Tac Toe"); 
       frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
       frame.add(new TicTacToePane()); 
       frame.pack(); 
       frame.setLocationRelativeTo(null); 
       frame.setVisible(true); 
      } 
     }); 
    } 

    public class TicTacToePane extends JPanel { 

     public TicTacToePane() { 
     } 

     @Override 
     public Dimension getPreferredSize() { 
      return new Dimension(500, 500); 
     } 

     @Override 
     protected void paintComponent(Graphics g) { 
      super.paintComponent(g); 
      Graphics2D g2d = (Graphics2D) g.create(); 
      //Drawing the GridLines 
      g2d.drawLine(168, 0, 168, 500); 
      g2d.drawLine(336, 0, 336, 500); 
      g2d.drawLine(0, 168, 500, 168); 
      g2d.drawLine(0, 336, 500, 336); 
      g2d.dispose(); 
     } 

    } 

} //End of TicTacToe Class  

作爲一般規則，建議不要直接從JFrame開始擴展，除了自定義繪畫問題之外，您不會向類中添加任何功能，而是將自己鎖定到單個用例中（很難再次使用該類）