java drag and drop

Question

I try to get familar with drag and drop in java but all the tutorials I found were... (getting me angry)

All I want is to drag a \"PublicUserLabel\" from a JList (in

Answer 1

The major issues I can see are you are mixing two different API's. You're using both the low level D'n'D API and the newer "component D'n'D" API.

Personally, the newer API annoys me, so I tend to avoid it.

I can't see why you need to transfer the label, when it would be better to transfer the underlying PublicUser object, but that's just me.

import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.GridBagLayout;
import java.awt.datatransfer.DataFlavor;
import java.awt.datatransfer.Transferable;
import java.awt.datatransfer.UnsupportedFlavorException;
import java.awt.dnd.DnDConstants;
import java.awt.dnd.DragGestureEvent;
import java.awt.dnd.DragGestureListener;
import java.awt.dnd.DragGestureRecognizer;
import java.awt.dnd.DragSource;
import java.awt.dnd.DragSourceDragEvent;
import java.awt.dnd.DragSourceDropEvent;
import java.awt.dnd.DragSourceEvent;
import java.awt.dnd.DragSourceListener;
import java.awt.dnd.DropTarget;
import java.awt.dnd.DropTargetDragEvent;
import java.awt.dnd.DropTargetDropEvent;
import java.awt.dnd.DropTargetEvent;
import java.awt.dnd.DropTargetListener;
import java.io.IOException;
import javax.swing.DefaultListModel;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class TestDnD {

    public static void main(String[] args) {
        new TestDnD();
    }

    public TestDnD() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException ex) {
                } catch (InstantiationException ex) {
                } catch (IllegalAccessException ex) {
                } catch (UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame("Test");
                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 JList list;

        public TestPane() {
            setLayout(new BorderLayout());
            list = new JList();
            DefaultListModel model = new DefaultListModel();
            model.addElement(new User("Shaun"));
            model.addElement(new User("Andy"));
            model.addElement(new User("Luke"));
            model.addElement(new User("Han"));
            model.addElement(new User("Liea"));
            model.addElement(new User("Yoda"));
            list.setModel(model);
            add(new JScrollPane(list), BorderLayout.WEST);

            DragGestureRecognizer dgr = DragSource.getDefaultDragSource().createDefaultDragGestureRecognizer(
                            list,
                            DnDConstants.ACTION_COPY_OR_MOVE,
                            new DragGestureHandler(list));

            JPanel panel = new JPanel(new GridBagLayout());
            add(panel);

            DropTarget dt = new DropTarget(
                            panel,
                            DnDConstants.ACTION_COPY_OR_MOVE,
                            new DropTargetHandler(panel),
                            true);

        }

    }

    public static class User {

        private String name;

        public User(String name) {
            this.name = name;
        }

        public String getName() {
            return name;
        }

        @Override
        public String toString() {
            return name;
        }

    }

    public static class UserTransferable implements Transferable {

        public static final DataFlavor USER_DATA_FLAVOR = new DataFlavor(User.class, "User");
        private User user;

        public UserTransferable(User user) {
            this.user = user;
        }

        @Override
        public DataFlavor[] getTransferDataFlavors() {
            return new DataFlavor[]{USER_DATA_FLAVOR};
        }

        @Override
        public boolean isDataFlavorSupported(DataFlavor flavor) {
            return USER_DATA_FLAVOR.equals(flavor);
        }

        @Override
        public Object getTransferData(DataFlavor flavor) throws UnsupportedFlavorException, IOException {
            Object value = null;
            if (USER_DATA_FLAVOR.equals(flavor)) {
                value = user;
            } else {
                throw new UnsupportedFlavorException(flavor);
            }
            return value;
        }

    }

    protected class DragGestureHandler implements DragGestureListener {

        private JList list;

        public DragGestureHandler(JList list) {
            this.list = list;
        }

        @Override
        public void dragGestureRecognized(DragGestureEvent dge) {
            Object selectedValue = list.getSelectedValue();
            if (selectedValue instanceof User) {
                User user = (User) selectedValue;
                Transferable t = new UserTransferable(user);
                DragSource ds = dge.getDragSource();
                ds.startDrag(
                                dge,
                                null,
                                t,
                                new DragSourceHandler());
            }

        }

    }

    protected class DragSourceHandler implements DragSourceListener {

        public void dragEnter(DragSourceDragEvent dsde) {
        }

        public void dragOver(DragSourceDragEvent dsde) {
        }

        public void dropActionChanged(DragSourceDragEvent dsde) {
        }

        public void dragExit(DragSourceEvent dse) {
        }

        public void dragDropEnd(DragSourceDropEvent dsde) {

            System.out.println("Drag ended...");

        }

    }

    protected class DropTargetHandler implements DropTargetListener {

        private JPanel panel;

        public DropTargetHandler(JPanel panel) {
            this.panel = panel;
        }

        public void dragEnter(DropTargetDragEvent dtde) {
            if (dtde.getTransferable().isDataFlavorSupported(UserTransferable.USER_DATA_FLAVOR)) {
                System.out.println("Accept...");
                dtde.acceptDrag(DnDConstants.ACTION_COPY_OR_MOVE);
            } else {
                System.out.println("Drag...");
                dtde.rejectDrag();
            }
        }

        public void dragOver(DropTargetDragEvent dtde) {
        }

        public void dropActionChanged(DropTargetDragEvent dtde) {
        }

        public void dragExit(DropTargetEvent dte) {
        }

        public void drop(DropTargetDropEvent dtde) {
            System.out.println("Dropped...");
            if (dtde.getTransferable().isDataFlavorSupported(UserTransferable.USER_DATA_FLAVOR)) {
                Transferable t = dtde.getTransferable();
                if (t.isDataFlavorSupported(UserTransferable.USER_DATA_FLAVOR)) {
                    try {
                        Object transferData = t.getTransferData(UserTransferable.USER_DATA_FLAVOR);
                        if (transferData instanceof User) {
                            User user = (User) transferData;
                            dtde.acceptDrop(DnDConstants.ACTION_COPY_OR_MOVE);
                            panel.add(new JLabel(user.getName()));
                            panel.revalidate();
                            panel.repaint();
                        } else {
                            dtde.rejectDrop();
                        }
                    } catch (UnsupportedFlavorException ex) {
                        ex.printStackTrace();
                        dtde.rejectDrop();
                    } catch (IOException ex) {
                        ex.printStackTrace();
                        dtde.rejectDrop();
                    }
                } else {
                    dtde.rejectDrop();
                }
            }
        }

    }

}