如何从Java中的按钮面板更改JPanel中的paintComponent

Question

我很难弄清楚如何在DrawPanel中更改绘画组件的颜色。

我们需要使用的方法是可以通过ButtonPanel更改绘画组件的颜色。

问题是我似乎找不到找到使处理程序识别面板并更改其颜色的方法。

如何从Java中的按钮面板更改JPanel中的paintComponent

main.java

import javax.swing.SwingUtilities;

public class main {
    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
                public void run() {
                new Window();
            }           
        });     
    }
}

Window.java

import javax.swing.JFrame;
import java.awt.BorderLayout;
import java.awt.Dimension;

public class Window extends JFrame {

    public Window () {
        // `super ' calls a function inherited from the parent class ( JFrame )
        super();
        setTitle("Callbacks");
        setSize (new Dimension(420, 350));

        // Make sure the window appears in the middle of your screen
        setLocationRelativeTo(null);

        // Determines what should happen when the frame is closed
        setDefaultCloseOperation (EXIT_ON_CLOSE);

        // Chooses a certain layout type for the elements in this frame
        getContentPane().setLayout (new BorderLayout());

        // TODO : add elements to the content pane
        DrawPanel dp = new DrawPanel ();
        ButtonPanel bp = new ButtonPanel ();

        // Places the DrawPanel in the center of the frame
        getContentPane (). add (dp , BorderLayout . CENTER );
        // Places the ButtonPanel in the top of the frame
        getContentPane (). add (bp , BorderLayout . NORTH );


        // Set the window to visible ! Yup ... This is necessary
        setVisible (true);
    }
}

DrawPanel.java

import java.awt.Color;
import java.awt.Graphics;

import javax.swing.*;

public class DrawPanel extends JPanel {

    private Color color;

    public DrawPanel(){
        super();
        color = Color.BLACK ;
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.setColor(getColor());
        g.fillRect(100 , 30, 200 , 200);
    }

}

ButtonPanel.java

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

public class ButtonPanel extends JPanel {


    public ButtonPanel () {
        super ();
        // Add a button to the panel . The argument to the JButton constructor
        // will become the text on the button .
        JButton b = new JButton ("Change color!");
        JButton c = new JButton ("Test");
        add (b);
        add (c);
        b.addActionListener(new InputHandler());

    }
}

InputHandler

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Random;

import com.sun.prism.paint.Color;

public class InputHandler implements ActionListener {

    public InputHandler() {
        // TODO Auto-generated constructor stub
    }

    public void actionPerformed (ActionEvent e) {
        // TODO : add code here that will
        // be ran when the button is clicked
    }
}

希望你们能帮助我或向正确的方向发送我。

Answer 1

使他们彼此成为朋友，以便Listener了解Panel ：

// Window
DrawPanel dp = new DrawPanel ();
ButtonPanel bp = new ButtonPanel (dp); // pass panel to button

然后：

public class ButtonPanel extends JPanel {       
    public ButtonPanel (DrawPanel d) {
        super ();
        // Add a button to the panel . The argument to the JButton constructor
        // will become the text on the button .
        JButton b = new JButton ("Change color!");
        JButton c = new JButton ("Test");
        add (b);
        add (c);
        b.addActionListener(new InputHandler(d)); // pass panel to listener    
    }
}

和：

public class InputHandler implements ActionListener {
    DrawPanel d;
    public InputHandler(DrawPanel d) {
        this.d = d;
    }    
    public void actionPerformed (ActionEvent e) {
        d.setColor(Color.BLUE); // whatever
        d.repaint(); // force painting
    }
}

然后：

public class DrawPanel extends JPanel {   
    private Color color;    
    public DrawPanel(){
        super();
        color = Color.BLACK ;
    }
    public void setColor(Color c) {
        this.color = c;
    }
    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.setColor(getColor());
        g.fillRect(100 , 30, 200 , 200);
    }    
}