Java Swing-拖放drawString文本

Question

I've had a look around for this problem but couldn't find an answer...

I currently have a JPanel in which I'm painting a load of unicode characters (music notes) using the Graphics2D g2.drawString() method.

I have an ArrayList of KeyPress objects, each of which contains one or more g2.drawString() calls.

So each KeyPress object is a music note and is painted on the JPanel.

How would I go about adding the functionality to enable the user to select and drag the objects?

Answer 1

Why not put your Strings in JLabels and simply drag them...

import java.awt.*;
import java.awt.event.*;
import java.util.Random;
import javax.swing.*;

public class DragLabelEg {
   private static final String[] LABEL_STRINGS = { "Do", "Re", "Me", "Fa",
         "So", "La", "Ti" };
   private static final int HEIGHT = 400;
   private static final int WIDTH = 600;
   private static final Dimension MAIN_PANEL_SIZE = new Dimension(WIDTH, HEIGHT);
   private static final int LBL_WIDTH = 60;
   private static final int LBL_HEIGHT = 40;
   private static final Dimension LABEL_SIZE = new Dimension(LBL_WIDTH,
         LBL_HEIGHT);
   private JPanel mainPanel = new JPanel();
   private Random random = new Random();

   public DragLabelEg() {
      mainPanel.setPreferredSize(MAIN_PANEL_SIZE);
      mainPanel.setLayout(null);

      MyMouseAdapter myMouseAdapter = new MyMouseAdapter();
      for (int i = 0; i < LABEL_STRINGS.length; i++) {
         JLabel label = new JLabel(LABEL_STRINGS[i], SwingConstants.CENTER);
         label.setSize(LABEL_SIZE);
         label.setOpaque(true);
         label.setLocation(random.nextInt(WIDTH - LBL_WIDTH),
               random.nextInt(HEIGHT - LBL_HEIGHT));
         label.setBackground(new Color(150 + random.nextInt(105), 150 + random
               .nextInt(105), 150 + random.nextInt(105)));
         label.addMouseListener(myMouseAdapter);
         label.addMouseMotionListener(myMouseAdapter);

         mainPanel.add(label);
      }
   }

   public JComponent getMainPanel() {
      return mainPanel;
   }

   private class MyMouseAdapter extends MouseAdapter {
      private Point initLabelLocation = null;
      private Point initMouseLocationOnScreen = null;

      @Override
      public void mousePressed(MouseEvent e) {
         JLabel label = (JLabel) e.getSource();
         // get label's initial location relative to its container
         initLabelLocation = label.getLocation();

         // get Mouse's initial location relative to the screen
         initMouseLocationOnScreen = e.getLocationOnScreen();
      }

      @Override
      public void mouseReleased(MouseEvent e) {
         initLabelLocation = null;
         initMouseLocationOnScreen = null;
      }

      @Override
      public void mouseDragged(MouseEvent e) {
         // if not dragging a JLabel
         if (initLabelLocation == null || initMouseLocationOnScreen == null) {
            return;
         }
         JLabel label = (JLabel) e.getSource();

         // get mouse's new location relative to the screen
         Point mouseLocation = e.getLocationOnScreen();

         // and see how this differs from the initial location.
         int deltaX = mouseLocation.x - initMouseLocationOnScreen.x;
         int deltaY = mouseLocation.y - initMouseLocationOnScreen.y;

         // change label's position by the same difference, the "delta" vector
         int labelX = initLabelLocation.x + deltaX;
         int labelY = initLabelLocation.y + deltaY;

         label.setLocation(labelX, labelY);
      }
   }

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

   private static void createGui() {
      JFrame frame = new JFrame("App");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(new DragLabelEg().getMainPanel());
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }
}

Answer 2

See the tutorial on supporting user interaction. It comes down to determining which (if any) objects were underneath the mouse when it was clicked and held. On a drag event, the selected object is moved and the canvas is repainted.

You can obtain the bounds of the string by using FontMetrics :

String text = "Hello world!";
Rectangle2D bounds = g2.getFontMetrics().getStringBounds(text, g2);

I assume the rectangle top-left will be (0, 0), so you need to add (x, y) to it (where x, y are the parameters you passed to drawString).

Answer 3

This example shows one way to select multiple objects, using keyboard or mouse, and drag them as a group. It manipulates arbitrary nodes rather than glyphs, but you may find it instructive.