问题描述

在 Java 中，当被拖动的项目是源代码控制本身时，执行拖放的最佳方式是什么?我知道控件也不过是数据，但区别确实会对 UI 产生影响.

In Java, what is the best way to perform drag and drop when the item being dragged is the source control itself? I know a control is nothing but data too, but the difference does have UI impacts.

我正在创建一个纸牌风格的游戏，其中我有从 JLabel 派生的 Card 类的卡片对象.我想将该卡拖放到一个尚未命名的目标控件上，从而将其拖到另一个位置.在拖动过程中，我希望卡片在视觉上随鼠标移动，并且在放下时我希望它移动到此目标对象或返回到其先前的位置.

I'm creating a solitaire-style game where I have card objects of class Card derived from JLabel. I want to drag that card to another location by dropping it onto a yet-to-be named Destination control. During the drag, I want the card to visually move with the mouse and when dropped I want it to either move to this destination object or return to its previous location.

我进行了各种 D-n-D 测试，但没有发现任何符合 Java 的 D-D 规则的东西.

I've done various D-n-D tests and haven't found anything that works under the proper rules of Java's D-D.

例如，如果我使用真正的 D-n-D 拖动卡片对象，我只能创建卡片的幻影图像而不是实体图像.此外，光标发生了变化，我宁愿它没有(我想我可以解决这个问题)，并且源代码控制仍然可见(尽管在拖动过程中应该很容易使其透明)

For example, if I drag the Card object using true D-n-D I can only create a ghosted image of the card and not a solid image. Also, the cursor changes and I'd rather it did not (I think I can fix that), and the source control remains visible (though it should be easy to make it transparent during the drag)

另一方面，我可以通过监听 MouseMotionListener.mouseDragged() 事件并手动将卡片移动到新位置来漂亮地拖动卡片.这很好用，但它没有遵循正确的 D-n-D，因为这不会通知其他控件的拖动.我想我可以创建自己的系统来通知其他控件，但这不会使用 Java 真正的 D-n-D.此外，如果我将真正的 Java d-n-d 内容与这种在 mouseDragged 期间从字面上移动卡片的方法混合在一起，那么我认为真正的 D-n-D 内容将永远不会起作用，因为从技术上讲，鼠标永远不会直接位于任何其他控件上，而不是被拖动的卡片.这个方向看起来就像一个粗略的黑客攻击.

On the other hand, I can drag the Card beautifully by listening for MouseMotionListener.mouseDragged() events and manually moving the Card to the new location. This works great, but it is not following proper D-n-D because this will not inform other controls of the drag. I figured I could either create my own system to notify the other controls, but that would not be using Java's real D-n-D. Also, if I mix the real Java d-n-d stuff with this method of literally moving the Card during mouseDragged then I assume the real D-n-D stuff will never work because the mouse will never technically be directly over any other control than the card being dragged. This direction just seems like a crude hack.

我希望这是有道理的.我一直在跟踪样本时遇到问题，因为它们看起来都非常不同，而我花费大量时间研究的样本似乎在 D-n-D 在 1.4 版中进行大修之前几年就过时了.

I hope this makes sense. I've been having problems following samples because they all seem very different, and one that I spent a great deal of time studying looks to be dated a couple years before D-n-D had its major overhaul in version 1.4.

推荐答案

在单个应用程序周围而不是在应用程序之间拖动组件的一种方法是使用 JLayeredPane.例如，请在此处查看我的代码:在屏幕上拖动 jlabel

One way to drag a component around a single application and not between applications is to use a JLayeredPane. For example please see my code here: dragging a jlabel around the screen

扑克牌示例可能如下所示(只要扑克牌图像保持有效！):

An example with playing cards could look like this (as long as the playing card image remains valid!):

import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import javax.imageio.ImageIO;
import javax.swing.*;

public class PlayingCardTest {


   public static void main(String[] args) {
      String pathToDeck = "http://www.jfitz.com/cards/classic-playing-cards.png";
      try {
         final List<ImageIcon> cardImgList = CreateCards.createCardIconList(pathToDeck);
         SwingUtilities.invokeLater(new Runnable() {
            public void run() {
               JFrame frame = new JFrame("Moving Cards");
               frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
               frame.add(new CardGameTable(cardImgList, frame));
               frame.pack();
               frame.setLocationRelativeTo(null);
               frame.setVisible(true);
            }
         });
      } catch (MalformedURLException e) {
         e.printStackTrace();
         System.exit(-1);
      } catch (IOException e) {
         e.printStackTrace();
         System.exit(-1);
      }
   }
}

@SuppressWarnings("serial")
class CardGameTable extends JLayeredPane {

   private static final int PREF_W = 600;
   private static final int PREF_H = 400;
   private static final Color BASE_COLOR = new Color(0, 80, 0);
   private static final int CARD_COUNT = 20;
   private static final int WIDTH_SHOWING = 20;

   private JPanel basePane = new JPanel(null);

   public CardGameTable(List<ImageIcon> cardImgList, final JFrame frame) {
      basePane.setSize(getPreferredSize());
      basePane.setBackground(BASE_COLOR);
      add(basePane, JLayeredPane.DEFAULT_LAYER);

      final MyMouseAdapter myMouseAdapter = new MyMouseAdapter(this, basePane);
      addMouseListener(myMouseAdapter);
      addMouseMotionListener(myMouseAdapter);

      for (int i = 0; i < CARD_COUNT; i++) {
         JLabel card = new JLabel(cardImgList.remove(0));
         card.setSize(card.getPreferredSize());
         int x = (PREF_W / 2) + WIDTH_SHOWING * (CARD_COUNT - 2 * i) / 2 - 
               card.getPreferredSize().width / 2;
         int y = PREF_H - card.getPreferredSize().height - WIDTH_SHOWING * 2;
         card.setLocation(x, y);
         basePane.add(card);
      }
   }

   @Override
   public Dimension getPreferredSize() {
      return new Dimension(PREF_W, PREF_H);
   }

}

class MyMouseAdapter extends MouseAdapter {
   private JLabel selectedCard = null;
   private JLayeredPane cardGameTable = null;
   private JPanel basePane = null;
   private int deltaX = 0;
   private int deltaY = 0;

   public MyMouseAdapter(JLayeredPane gameTable, JPanel basePane) {
      this.cardGameTable = gameTable;
      this.basePane = basePane;
   }

   @Override
   public void mousePressed(MouseEvent mEvt) {
      Component comp = basePane.getComponentAt(mEvt.getPoint());
      if (comp != null && comp instanceof JLabel) {
         selectedCard = (JLabel) comp;
         basePane.remove(selectedCard);
         basePane.revalidate();
         basePane.repaint();

         cardGameTable.add(selectedCard, JLayeredPane.DRAG_LAYER);
         cardGameTable.revalidate();
         cardGameTable.repaint();
         deltaX = mEvt.getX() - selectedCard.getX();
         deltaY = mEvt.getY() - selectedCard.getY();
      }
   }

   @Override
   public void mouseReleased(MouseEvent mEvt) {
      if (selectedCard != null) {
         cardGameTable.remove(selectedCard);
         cardGameTable.revalidate();
         cardGameTable.repaint();

         basePane.add(selectedCard, 0);
         basePane.revalidate();
         basePane.repaint();
         selectedCard = null;
      }
   }

   @Override
   public void mouseDragged(MouseEvent mEvt) {
      if (selectedCard != null) {
         int x = mEvt.getX() - deltaX;
         int y = mEvt.getY() - deltaY;
         selectedCard.setLocation(x, y);
         cardGameTable.revalidate();
         cardGameTable.repaint();
      }
   }
}

class CreateCards {
   private static final int SUIT_COUNT = 4;
   private static final int RANK_COUNT = 13;

   public static List<ImageIcon> createCardIconList(String pathToDeck)
         throws MalformedURLException, IOException {
      BufferedImage fullDeckImg = ImageIO.read(new URL(pathToDeck));
      int width = fullDeckImg.getWidth();
      int height = fullDeckImg.getHeight();
      List<ImageIcon> iconList = new ArrayList<ImageIcon>();

      for (int suit = 0; suit < SUIT_COUNT; suit++) {
         for (int rank = 0; rank < RANK_COUNT; rank++) {
            int x = (rank * width) / RANK_COUNT;
            int y = (suit * height) / SUIT_COUNT;
            int w = width / RANK_COUNT;
            int h = height / SUIT_COUNT;
            BufferedImage cardImg = fullDeckImg.getSubimage(x, y, w, h);
            iconList.add(new ImageIcon(cardImg));
         }
      }
      Collections.shuffle(iconList);
      return iconList;
   }
}

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