Question

我试图在点击JButton时显示图像，但在执行时，单击按钮时不显示图像。

    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

..单击JButton时显示图像，但执行时单击按钮时不显示图像。

使用显示here的JToggleButton。

Answer 2

按钮应该设置布尔变量，但是在动作预先形成的方法之后永远不会调用paint2。其次，它甚至不会绘制任何东西，它永远不会得到图形并会导致NPE。

Answer 3

您应该覆盖JFrame.paint(Graphics g)方法。每当您想要刷新JFrame实例的内容时，请调用JFrame.repaint()方法。

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);
            }
        });
    }
}

单击JButton时显示图像

4 个答案: