绘制另一个组件

Question

I have a homework to do but there is not enough information and I'm stuck right now... Here is the issue, I have three classes :

• "ChoicePanel" extends JPanel and add buttons to select a color with a JComboBox

   public class ChoicePanel extends JPanel{ Draw dessin; public ChoicePanel(Draw df) { dessin = df; ... // couleurs final JComboBox<String> couleurs = new JComboBox<>(new String[] {"bleu", "jaune", "rouge"}); add(couleurs); } /** Know what color is selected */ private Color determineCouleur(int indice){ switch (indice) { case 0: return Color.BLUE; case 1: return Color.YELLOW; case 2: return Color.RED; default: return Color.BLACK; } } } 

• "Draw" extends JPanel and stock all outline and paint them

• "Main" create the frame with those classes included

I have to set Draw as a MouseMotionListener but i can't get the color selected in ChoixePanel because the JComobox is created in the construcor and I can't set it to a field. So how can I check ChoicePanel's buttons values from Draw ?

Every answer will be very helpfull !

Answer 1

The goal of the exercise may be to help you learn about scope and access in Java. Let's refactor the example seen here to meet your requirements.

• A ChoicePanel needs a way to update an instance of the Draw panel; you can pass a reference as a parameter to the panel's constructor or the factory method shown below.

   public static JPanel create(Draw draw) {…} 

• In the combo's action listener set the color on draw ; optionally invoke draw.repaint() if the change is not to a bound property such as background color.

   Hue h = (Hue) colors.getSelectedItem(); draw.setBackground(h.getColor()); //draw.repaint(); 

• Because Draw may contain no components, override getPreferredSize() as shown here and below.

• I can't create a private class…

  For convenience in running the example below, ChoicePanel and Draw are included as private static members. Simply move each to its own file, absent the modifiers , to get stand-alone classes having package-private access from Main .

   JFrame f = new JFrame("Main"); Draw d = new Draw(); f.add(d, BorderLayout.CENTER); f.add(ChoicePanel.create(d), BorderLayout.SOUTH); 

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JPanel;

/**
 * @see https://stackoverflow.com/a/5663782/230513
 */
public class Main {

    private static class ChoicePanel {

        public static JPanel create(Draw draw) {
            JPanel p = new JPanel();
            final JComboBox colors = new JComboBox();
            for (Hue h : Hue.values()) {
                colors.addItem(h);
            }
            colors.addActionListener((ActionEvent e) -> {
                Hue h = (Hue) colors.getSelectedItem();
                draw.setBackground(h.getColor());
            });
            p.add(colors);
            return p;
        }
    }

    private static class Draw extends JPanel {

        public Draw() {
            this.setBackground(Hue.values()[0].getColor());
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(320, 240);
        }
    }

    public enum Hue {

        Cyan(Color.cyan), Magenta(Color.magenta), Yellow(Color.yellow),
        Red(Color.red), Green(Color.green), Blue(Color.blue);

        private final Color color;

        private Hue(Color color) {
            this.color = color;
        }

        public Color getColor() {
            return color;
        }
    }

    private void display() {
        JFrame f = new JFrame("Main");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        Draw d = new Draw();
        f.add(d, BorderLayout.CENTER);
        f.add(ChoicePanel.create(d), BorderLayout.SOUTH);
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(() -> {
            new Main().display();
        });
    }
}