单击JButton显示图像

Question

Im trying to display an image upon clicking a JButton but upon execution the image is not displayed when button is clicked.

    import javax.swing.JButton;
import javax.swing.JFrame;
import java.awt.Color;
import java.awt.Container;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.Graphics;
import java.awt.Image;
import javax.swing.ImageIcon;
import javax.swing.JApplet;
import java.awt.*;

public class new2 extends JFrame implements ActionListener
{
private boolean b1,b2;  

Container contentPane= getContentPane();
JButton awar=new JButton("@war");
JButton arrow=new JButton("arrow");
private Image image1,image2;

public new2()
    {
    setSize(400, 300);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        contentPane.setLayout(new FlowLayout());

        awar.addActionListener(this);
        contentPane.add(awar).setVisible(true);

        arrow.addActionListener(this);
        contentPane.add(arrow).setVisible(true);

        }

public void init()
    {


    image1=Toolkit.getDefaultToolkit().getImage("@war.jpeg");
    image2=Toolkit.getDefaultToolkit().getImage("arrow.gif");
    }


public void paint(Graphics g)
{

    if(b1==true)
    {
    g.drawImage(image1,0,0,this);
    }
    else if(b2==true)
    {
    g.drawImage(image2,0,0,this);
    }

}

public void actionPerformed(ActionEvent event)
{

        String actionCommand = event.getActionCommand();

    if(actionCommand.equals("@war"))
    {
    b1=true;
    }
    else if(actionCommand.equals("arrow"))
    {
    b2=true;
    }
}

public static void main(String args[])
{
new2 m=new new2();
m.setVisible(true);
}

}

Answer 1

..display an image upon clicking a JButton but upon execution the image is not displayed when button is clicked.

Use a JToggleButton as shown here .

Answer 2

The buttons should set the boolean variables, but your paint2 is never called after the action preformed method. Secondly, it doesn't really even paint anything, it never gets graphics and will cause NPEs.

Answer 3

You should override the JFrame.paint(Graphics g) method. Whenever you want to refresh the content of the JFrame instance call the JFrame.repaint() method.

Answer 4

/**
 * 
 */
package com.samples;

import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.EventQueue;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.WindowConstants;

/**
 * @author
 *
 */
public class MyFrame extends JFrame implements ActionListener {

    private static String SHOW_ACTION = "show";
    private static String HIDE_ACTION = "hide";

    private Image image = null;
    private boolean showImage = false;

    public MyFrame(String filename) {
        setTitle("MyWindow");
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        setSize(800, 600);

        this.image = new ImageIcon(filename).getImage();

        Container container = getContentPane();
        container.setLayout(new BorderLayout());
        container.add(createControls(), BorderLayout.SOUTH);
    }

    private JPanel createControls() {
        JButton showButton = new JButton("Show");
        showButton.addActionListener(this);
        showButton.setActionCommand(SHOW_ACTION);

        JButton hideButton = new JButton("Hide");
        hideButton.addActionListener(this);
        hideButton.setActionCommand(HIDE_ACTION);

        JPanel panel = new JPanel();
        panel.setLayout(new FlowLayout(FlowLayout.CENTER));

        panel.add(showButton);
        panel.add(hideButton);

        return panel;
    }

    @Override
    public void paint(Graphics g) {
        super.paint(g);

        if (showImage) {
            g.drawImage(image, 0, 0, image.getWidth(null), image.getHeight(null), null);
        }
    }

    @Override
    public void actionPerformed(ActionEvent event) {
        String actionCommand = event.getActionCommand();

        if (SHOW_ACTION.equals(actionCommand)) {
            showImage = true;
        } else if (HIDE_ACTION.equals(actionCommand)) {
            showImage = false;
        }

        repaint();
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                MyFrame frame = new MyFrame("resources/image.jpg");
                frame.setVisible(true);
            }
        });
    }
}