java - JFrame、JPanel、paintComponent 如何

Question

1. 您好，我有以下类(class)，我想要显示内容(paintComponentor 具有来自paint 类的矩形的面板)在我的 JFrame 中。我已经尝试找出如何实现这一目标看看这个论坛上发布的不同例子，但是这个对我没有帮助我需要简单的例子，比如框架内的面板绘制组件或类似的东西以了解应该如何工作! 附:不要把我卡在树上，因为我是新手，只是问问题!!!

   [我想要这样的东西][1]

   package scp;
   
   import java.awt.*;
   
   import javax.swing.*;
   
   public class Panel extends JPanel {
       public Panel() {
           //this.setPreferredSize(new Dimension(200,200));
           //panel = new Panel();
           setVisible(true);
           setLayout(new FlowLayout());
           setSize(200, 300);
           getRootPane();
       }
       @Override
       public void paintComponent(Graphics g){
           g.drawString("HEY",20,20);
           g.drawRect(200, 200, 200, 200); 
       }
   
   }
   
   and
   
   package scp;
   
   import javax.swing.JFrame;
   import javax.swing.JButton;
   
   import java.awt.Color;
   import java.awt.FlowLayout;
   import java.awt.event.ActionListener;
   import java.awt.event.ActionEvent;
   import java.beans.EventHandler;
   
   public class Frame extends JFrame {
   
       JButton redButton;
       JButton blueButton;
   
       public Frame()
       {
           super("EventHandling");
           setLayout(new FlowLayout());
           redButton = new JButton("Red");
           add(redButton);
           blueButton = new JButton("Blue");
           add(blueButton);
   
           EventHandler h = new EventHandler();
   
           redButton.addActionListener(h);
           blueButton.addActionListener(h);
   
       }
   
       private class EventHandler implements ActionListener
       {
           public void actionPerformed(ActionEvent e)
           {
               if (e.getSource()==redButton)
                   getContentPane().setBackground(Color.RED);
               else if(e.getSource()==blueButton)
                   getContentPane().setBackground(Color.BLUE);
           }
       }
   
   }
   
   and
   
   package scp;
   
   import javax.swing.JFrame;
   
   public class EventHandling {
   
       public static void main(String[] args) {
   
           Frame f = new Frame();
           f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
           f.setSize(800,600);
           f.setVisible(true);
           f.getContentPane().add(new Panel());
       }
   
   }
   

   [1]:/image/OJTrq.png

Answer 1

首先看一下:

• Painting in AWT and Swing
• Performing Custom Painting
• 2D Graphics

这可能是我能做到的最简单的......

import java.awt.Color;
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 Test {

    public static void main(String[] args) {
        new Test();
    }

    public Test() {
        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("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        public TestPane() {
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            int width = getWidth() - 100;
            int height = getHeight() - 100;
            int x = (getWidth() - width) / 2;
            int y = (getHeight() - height) / 2;
            g2d.setColor(Color.RED);
            g2d.drawRect(x, y, width, height);
            g2d.dispose();
        }

    }

}

复合示例

此示例使用 outer 面板，该面板应用了空边框，这会推送 outer 面板边缘的内容。

内部面板(与上一个示例相比没有变化)，应用了浅灰色边框以便您可以看到它，红色矩形仍然由面板 paintComponent 方法绘制。

import java.awt.BorderLayout;
import java.awt.Color;
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;
import javax.swing.border.EmptyBorder;
import javax.swing.border.LineBorder;

public class Test {

    public static void main(String[] args) {
        new Test();
    }

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

                JPanel outer = new JPanel(new BorderLayout()) {
                    @Override
                    public Dimension getPreferredSize() {
                        return new Dimension(400, 400);
                    }
                };

                outer.setBorder(new EmptyBorder(50, 50, 50, 50));

                TestPane tp = new TestPane();
                tp.setBorder(new LineBorder(Color.LIGHT_GRAY));

                outter.add(tp);

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(outer);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        public TestPane() {

        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            int width = getWidth() - 100;
            int height = getHeight() - 100;
            int x = (getWidth() - width) / 2;
            int y = (getHeight() - height) / 2;
            g2d.setColor(Color.RED);
            g2d.drawRect(x, y, width, height);
            g2d.dispose();
        }

    }

}