java - 使用旧实例的paintComponent

Question

我正在使用 swing 在 java 中制作一个掷骰子程序。我有 4 节课:

死

public class Die{
private int faceValue;

public Die(){
    System.out.println("Creating new Dice Object");
    setValue(roll());
}

public int roll() {
    int val = (int) (6 * Math.random() + 1);
    setValue(val);
    return val;
}

public int getValue() {
    return faceValue;
}

public void setValue(int spots) {
    faceValue = spots;
}
}

死亡脸

public class DieFace {
private int spotDiam,wOffset,hOffset,w,h;
public int faceValue;

public DieFace(){
    Die die = new Die();
    this.faceValue = die.getValue();
}

public void draw(Graphics g, int paneWidth, int paneHeight){
    //draw information
}
}

DieFace组件

public class DieFaceComponent extends JComponent{
private static final long serialVersionUID = 1L;

DieFace face; 

public DieFaceComponent(){
    face = new DieFace();
    System.out.println("DIEFACE" + face.faceValue);
    repaint();
}

public void paintComponent(Graphics g){
    revalidate();
    face.draw(g,super.getWidth(),super.getHeight());  

}
}

DieFaceViewer

public class DieFaceViewer{

static DieFaceComponent component;
static JFrame frame = new JFrame(); // Create a new JFrame object

public static void main(String[] args){
    final int FRAME_WIDTH = 500;
    final int FRAME_HEIGHT = 500;
    frame.setSize(FRAME_WIDTH, FRAME_HEIGHT); // Set initial size 
    frame.setTitle("Dice Simulator Version 1.0"); // Set title
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); // Set default close operation
    component = new DieFaceComponent(); // Create a new DieFaceComponent object
    frame.setLayout(new BorderLayout());
    JButton btnRoll = new JButton("Roll!");
    btnRoll.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            component = new DieFaceComponent();
        }
    });

    frame.add(component, BorderLayout.CENTER); // Add DieFaceComponent object to frame
    frame.add(btnRoll, BorderLayout.SOUTH);
    frame.setVisible(true); // Set frame to visible
}
}

我的问题是，即使每次按下 btnRoll 时都会创建一个新的 Die、DieFace 和 DieFaceComponent 对象，用于绘制组件的值仍与初始实例相同。我是不是做错了什么？提前致谢

Answer 1

您在 ActionListener 中创建了 DieFaceComponent 的新实例，但对它不执行任何操作，它从未添加到任何内容中，因此它永远不可见。更好的解决方案将允许您触发对 DieFaceComponent 的更改，从而触发对 DieFace 的更改，从而触发对 Die 的更改，并拥有整个事情只是重绘本身，例如......

public class Die {

    private int faceValue;

    public Die() {
        System.out.println("Creating new Dice Object");
        //setValue(roll());
        roll(); // Roll sets the value any way :P
    }

    public int roll() {
        int val = (int) (6 * Math.random() + 1);
        setValue(val);
        return val;
    }

    public int getValue() {
        return faceValue;
    }

    public void setValue(int spots) {
        faceValue = spots;
    }
}

public class DieFace {

    private int spotDiam, wOffset, hOffset, w, h;
    //public int faceValue;
    private Die die;

    public DieFace() {
        die = new Die();
        //Die die = new Die();
        // This is pointless, as you should simply as die for it's value
        // when ever you need it...
        //this.faceValue = die.getValue();
    }

    public void roll() {
        die.roll();
    }

    public void draw(Graphics g, int paneWidth, int paneHeight) {
        //draw information
    }
}

public class DieFaceComponent extends JComponent {

    private static final long serialVersionUID = 1L;

    DieFace face;

    public DieFaceComponent() {
        face = new DieFace();
        //System.out.println("DIEFACE" + face.faceValue);
        // Pointless, as you've probably not actually been added to anything
        // that could actuallyt paint you anyway...
        //repaint();
    }

    public void roll() {
        face.roll();
        repaint();
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        //revalidate();
        face.draw(g, super.getWidth(), super.getHeight());

    }
}

现在，您可以在 DieFaceComponent 上调用 roll，这将在 DieFace 上调用 roll，后者将调用 roll on Die，这将更新实际值。然后，DieFaceComponent 将安排一次重绘，以确保它在屏幕上更新。

然后你可以使用它，比如......

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class DiceRoller {

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

    public DiceRoller() {
        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 DiePane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class DiePane extends JPanel {

        public DiePane() {
            setLayout(new BorderLayout());

            DieFaceComponent component = new DieFaceComponent();
            JButton roll = new JButton("Roll");
            roll.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    component.roll();
                }
            });
            add(component);
            add(roll, BorderLayout.SOUTH);
        }

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

    }

}

现在，更好的解决方案是将 Die 作为您的主要入口点，允许它向感兴趣的各方生成通知并让他们自行更新

也许像...

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.beans.PropertyChangeSupport;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class DiceRoller {

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

    public DiceRoller() {
        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 DiePane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class DiePane extends JPanel {

        public DiePane() {
            setLayout(new BorderLayout());

            Die die = new Die();
            DieFaceComponent component = new DieFaceComponent(die);
            JButton roll = new JButton("Roll");
            roll.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    die.roll();
                }
            });
            add(component);
            add(roll, BorderLayout.SOUTH);
        }

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

        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            g2d.dispose();
        }

    }

    public class Die {

        private PropertyChangeSupport propertyChangeSupport;
        private int faceValue;

        public Die() {
            propertyChangeSupport = new PropertyChangeSupport(this);
            System.out.println("Creating new Dice Object");
            //setValue(roll());
            roll(); // Roll sets the value any way :P
        }

        public int roll() {
            int val = (int) (6 * Math.random() + 1);
            setValue(val);
            return val;
        }

        public int getValue() {
            return faceValue;
        }

        public void setValue(int spots) {
            int old = faceValue;
            faceValue = spots;
            propertyChangeSupport.firePropertyChange("value", old, faceValue);
        }

        public void addPropertyChangeListener(PropertyChangeListener listener) {
            propertyChangeSupport.addPropertyChangeListener(listener);
        }

        public void removePropertyChangeListener(PropertyChangeListener listener) {
            propertyChangeSupport.addPropertyChangeListener(listener);
        }
    }

    public class DieFace {

        private int spotDiam, wOffset, hOffset, w, h;
        private Die die;

        public DieFace(Die die) {
            this.die = die
        }

        public void draw(Graphics g, int paneWidth, int paneHeight) {
            //draw information
        }
    }

    public class DieFaceComponent extends JComponent {

        private static final long serialVersionUID = 1L;

        private DieFace face;

        public DieFaceComponent(Die die) {
            face = new DieFace(die);
            die.addPropertyChangeListener(new PropertyChangeListener() {
                @Override
                public void propertyChange(PropertyChangeEvent evt) {
                    repaint();
                }
            });
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            //revalidate();
            face.draw(g, super.getWidth(), super.getHeight());

        }
    }

}

这是 Observer Pattern 的一个简单示例，其中Die是信息的生成器，其他每个人都有兴趣知道它何时发生变化。它也是模型- View - Controller 范式的变体