更新GUI面板，Java

Question

我是Java GUI的初学者，在使面板更新所需的方式时遇到了一些麻烦。 基本上，当用户单击我的GUI中的按钮之一时，当前显示在屏幕上的形状应更改为与按钮按下相对应的任何形状。 我的代码如下。 更新后的形状在可以显示之前被原始形状覆盖的问题。

我很确定问题出在我的ButtonListeners上。 我添加了打印语句，以查看何时调用了不同的绘制方法，这是单击一个按钮后的结果：

RECT RECT RECT ddd椭圆形

显然更新正在进行中，但是随后将被原始形状覆盖！ 有人可以告诉我为什么发生最后的覆盖吗？

我已经包含了供参考的FigurePanel类。

import java.awt.BorderLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JLabel;
import javax.swing.JPanel;

public class miniCADFrame extends JPanel {

    private ButtonPanel buttons = new ButtonPanel();
    private CanvasPanel canvas = new CanvasPanel();

    public miniCADFrame() {
         //Constructor, creates the mother panel
         this.setLayout(new BorderLayout());
         this.add (canvas,BorderLayout.CENTER);
    }
    //******** BUTTONLISTENER************************
    private class ButtonListener implements ActionListener {

        @Override
        public void actionPerformed(ActionEvent event) {    //Paint the figure associated with the button click
                canvas.add(new FigurePanel(FigurePanel.OVAL), BorderLayout.CENTER);
                canvas.revalidate();
                canvas.repaint();
                System.out.println("ddd");

            }
    }

    private class ButtonPanel extends JPanel {

        private JButton[] Jbuttons = new JButton[11];
        //Constructor
        ButtonPanel() {

            setLayout(new GridLayout(4, 4)); 

            // Create buttons to attach to the buttons panel
            Jbuttons[0] = new JButton("Change Colour");
            Jbuttons[1] = new JButton("Up");
            Jbuttons[2] = new JButton("Text");
            Jbuttons[3] = new JButton("Left");
            Jbuttons[4] = new JButton("Enlarge");
            Jbuttons[5] = new JButton("Right");
            Jbuttons[6] = new JButton("Rectangle");
            Jbuttons[7] = new JButton("Down");
            Jbuttons[8] = new JButton("Circle");
            Jbuttons[9] = new JButton("Save");
            Jbuttons[10] = new JButton("Load");

            //Add the buttons to the buttons panel
            for (int i=0; i<11; i++) {
                Jbuttons[i].addActionListener(new ButtonListener());
                add(Jbuttons[i]);
            }
    }
    }

class CanvasPanel extends JPanel {

        //Constructor
        CanvasPanel() {
            // Create "canvas" to hold a label for the buttons panel along with the button panel itself
             this.setLayout(new BorderLayout());
             this.add(new JLabel("CONTROL PANEL"),BorderLayout.NORTH);
             this.add(buttons, BorderLayout.WEST); //add the button panel to the canvas panel

             //test
             this.add(new FigurePanel(FigurePanel.RECTANGLE), BorderLayout.CENTER);
        }
}
}

FigurePanel类：

import java.awt.*;
import javax.swing.JPanel;

public class FigurePanel extends JPanel {

    // Define constants
     public static final int LINE = 1;
     public static final int RECTANGLE = 2;
     public static final int OVAL = 4;

     private int type;

     /** Construct a default FigurePanel */
     public FigurePanel() {
     }

     /** Construct a FigurePanel with the specified type */
     public FigurePanel(int type) {
     this.type = type;
     }

     /** Draw a figure on the panel */
     protected void paintComponent(Graphics g) {
         //Create blank canvas
         super.paintComponent(g);

         // Get the appropriate size for the figure
         int width = getWidth();//width of the component
         int height = getHeight();//height of the component

        switch (type) {
         case LINE: // Display a single line
             g.drawLine(10, 10, width - 10, height - 10);
             break;
         case RECTANGLE: // Display a rectangle
             g.drawRect((int)(0.1 * width), (int)(0.1 * height),
             (int)(0.8 * width), (int)(0.8 * height));
             break;
         case OVAL: // Display an oval
          g.drawOval((int)(0.1 * width), (int)(0.1 * height),
          (int)(0.8 * width), (int)(0.8 * height));
         }
 }
      /** Set a new figure type */
      public void setType(int type) {
      this.type = type;
      }

      /** Return figure type */
      public int getType() {
      return type;
      }

      /** Specify preferred size */
      public Dimension getPreferredSize() {
          return new Dimension(80, 80);
      }
}

最后，这是我的框架类：

import java.awt.*;

import javax.swing.*;

public class miniCAD extends JFrame {
    //Constructor for our extended frame class

    public miniCAD() { 

    //Initialize our custom frame
    miniCADFrame frame = new miniCADFrame();    

    add(frame, BorderLayout.CENTER);

    }

     /** Main method */
     public static void main(String[] args) {
     miniCAD frame = new miniCAD();
     frame.setTitle("minCAD");
     frame.setSize(1000, 1000);
     frame.setLocationRelativeTo(null); // Center the frame
     frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
     frame.setVisible(true);
     }
 }

谢谢您的帮助！

Answer 1

我可以提出两个可能的原因。

1. 调用canvas.revalidate(); 在canvas.repaint();之前canvas.repaint(); 更新布局。
2. 检查用于绘制面板内容的颜色。