问题
I'm trying to make it so I can click and drag an ImageIcon (in this case a card image but I'd like to learn how to do it generally) around the window but I don't really know how. I would like to be able to click and hold the mouse botton, drag the ImageIcon, and have stay where it is whn I release the mouse botton.
This is the code I have so far:
import javax.swing.*;
import java.awt.*;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
public class MyFirstClass
{
public static void main(String[] args)
{
//load the card image from the gif file.
final ImageIcon cardIcon = new ImageIcon("cardImages/tenClubs.gif");
JLabel lbl = new JLabel(cardIcon);
//create a panel displaying the card image
JPanel panel = new JPanel()
{
//paintComponent is called automatically by the JRE whenever
//the panel needs to be drawn or redrawn
public void paintComponent(Graphics g) {
super.paintComponent(g);
cardIcon.paintIcon(this, g, 20, 20);
}
};
lbl.setTransferHandler(null);
MouseListener listener = new MouseAdapter() {
public void mousePressed(MouseEvent me) {
JComponent comp = (JComponent) me.getSource();
TransferHandler handler = comp.getTransferHandler();
handler.exportAsDrag(comp, me, TransferHandler.COPY);
}
};
lbl.addMouseListener(listener);
//create & make visible a JFrame to contain the panel
JFrame window = new JFrame("Cards");
window.add(panel);
window.setPreferredSize(new Dimension(200,200));
window.pack();
window.setVisible(true);
}
}
Thank you.
回答1:
The problem is you're mixing paradigms...not to mention you never seem to add lbl to anything, so it could never possible receive events and the fact that the panel is under the control of a layout manager, making moving a component very difficult...
In Swing there are at least three different ways to drag something, which you use comes down to what it is you want to achieve.
You can...
Use MouseListener and MouseMotitionListener to perform the actions manually. This is useful if you want to physical place an object somewhere within the container, like you are trying to do, for example...
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
public class DragMe {
public static void main(String[] args) {
new DragMe();
}
public DragMe() {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
}
JFrame frame = new JFrame("Testing");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new BorderLayout());
frame.add(new TestPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class TestPane extends JPanel {
private BufferedImage img;
private Point imgPoint = new Point(0, 0);
public TestPane() {
try {
img = ImageIO.read(new File("Computer.png"));
} catch (IOException ex) {
ex.printStackTrace();
}
MouseAdapter ma = new MouseAdapter() {
private Point offset;
@Override
public void mousePressed(MouseEvent e) {
Rectangle bounds = getImageBounds();
Point mp = e.getPoint();
if (bounds.contains(mp)) {
offset = new Point();
offset.x = mp.x - bounds.x;
offset.y = mp.y - bounds.y;
}
}
@Override
public void mouseReleased(MouseEvent e) {
offset = null;
}
@Override
public void mouseDragged(MouseEvent e) {
if (offset != null) {
Point mp = e.getPoint();
imgPoint.x = mp.x - offset.x;
imgPoint.y = mp.y - offset.y;
repaint();
}
}
};
addMouseListener(ma);
addMouseMotionListener(ma);
}
protected Rectangle getImageBounds() {
Rectangle bounds = new Rectangle(0, 0, 0, 0);
if (img != null) {
bounds.setLocation(imgPoint);
bounds.setSize(img.getWidth(), img.getHeight());
}
return bounds;
}
@Override
public Dimension getPreferredSize() {
return new Dimension(200, 200);
}
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
if (img != null) {
Graphics2D g2d = (Graphics2D) g.create();
g2d.drawImage(img, imgPoint.x, imgPoint.y, this);
g2d.dispose();
}
}
}
}
You can...
Use the core Drag-n-Drop APIs. This very low level and provides you are wide variety of flexibility. You can drag components, data or sorts of stuff based on your needs...
For example:
- java drag and drop
- How to drag and drop JPanel with its components
- move component after drag and drop
And if you're really adventurous, you can take a look at these...
- My Drag Image is Better than Yours
- Drop Target Navigation, or You Drag Your Bags, Let the Doorman Get the Door
- Smooth JList Drop Target Animation
You can..
Make use of the new transfer API. The intention of this API is to make it easier to transfer data around the application. While, technically, it would be possible to move a component this way, this is not it's intention.
Take a look at...
- Drag and Drop and Data Transfer
- Introduction to the DnD API
- How to drag and drop with Java 2, Part 1
For more details...
来源：https://stackoverflow.com/questions/21616900/imageicon-click-and-drag-around-the-window