Extend TransferHandler to handle drag and drop event

Description

Demo Code

/*//from w  ww  .  j a  va 2  s.  c  om
 * DropDemo.java requires the following file:
 *     ListTransferHandler.java
 */
import javax.swing.*;
import java.awt.*;
import java.awt.datatransfer.*;
import java.awt.event.*;
/*
 * ListTransferHandler.java is used by the DropDemo example.
 */
import javax.swing.*;
import java.awt.*;
import java.awt.datatransfer.*;

class ListTransferHandler extends TransferHandler {
    private int[] indices = null;
    private int addIndex = -1; //Location where items were added
    private int addCount = 0; //Number of items added.

    public boolean canImport(TransferHandler.TransferSupport info) {
        // Check for String flavor
        if (!info.isDataFlavorSupported(DataFlavor.stringFlavor)) {
            return false;
        }
        return true;
    }

    protected Transferable createTransferable(JComponent c) {
        return new StringSelection(exportString(c));
    }

    public int getSourceActions(JComponent c) {
        return TransferHandler.COPY_OR_MOVE;
    }

    public boolean importData(TransferHandler.TransferSupport info) {
        if (!info.isDrop()) {
            return false;
        }

        JList list = (JList) info.getComponent();
        DefaultListModel listModel = (DefaultListModel) list.getModel();
        JList.DropLocation dl = (JList.DropLocation) info.getDropLocation();
        int index = dl.getIndex();
        boolean insert = dl.isInsert();

        // Get the string that is being dropped.
        Transferable t = info.getTransferable();
        String data;
        try {
            data = (String) t.getTransferData(DataFlavor.stringFlavor);
        } catch (Exception e) {
            return false;
        }

        // Perform the actual import.  
        if (insert) {
            listModel.add(index, data);
        } else {
            listModel.set(index, data);
        }
        return true;
    }

    protected void exportDone(JComponent c, Transferable data, int action) {
        cleanup(c, action == TransferHandler.MOVE);
    }

    //Bundle up the selected items in the list
    //as a single string, for export.
    protected String exportString(JComponent c) {
        JList list = (JList) c;
        indices = list.getSelectedIndices();
        Object[] values = list.getSelectedValues();

        StringBuffer buff = new StringBuffer();

        for (int i = 0; i < values.length; i++) {
            Object val = values[i];
            buff.append(val == null ? "" : val.toString());
            if (i != values.length - 1) {
                buff.append("\n");
            }
        }

        return buff.toString();
    }

    //Take the incoming string and wherever there is a
    //newline, break it into a separate item in the list.
    protected void importString(JComponent c, String str) {
        JList target = (JList) c;
        DefaultListModel listModel = (DefaultListModel) target.getModel();
        int index = target.getSelectedIndex();

        //Prevent the user from dropping data back on itself.
        //For example, if the user is moving items #4,#5,#6 and #7 and
        //attempts to insert the items after item #5, this would
        //be problematic when removing the original items.
        //So this is not allowed.
        if (indices != null && index >= indices[0] - 1
                && index <= indices[indices.length - 1]) {
            indices = null;
            return;
        }

        int max = listModel.getSize();
        if (index < 0) {
            index = max;
        } else {
            index++;
            if (index > max) {
                index = max;
            }
        }
        addIndex = index;
        String[] values = str.split("\n");
        addCount = values.length;
        for (int i = 0; i < values.length; i++) {
            listModel.add(index++, values[i]);
        }
    }

    //If the remove argument is true, the drop has been
    //successful and it's time to remove the selected items 
    //from the list. If the remove argument is false, it
    //was a Copy operation and the original list is left
    //intact.
    protected void cleanup(JComponent c, boolean remove) {
        if (remove && indices != null) {
            JList source = (JList) c;
            DefaultListModel model = (DefaultListModel) source.getModel();
            //If we are moving items around in the same list, we
            //need to adjust the indices accordingly, since those
            //after the insertion point have moved.
            if (addCount > 0) {
                for (int i = 0; i < indices.length; i++) {
                    if (indices[i] > addIndex) {
                        indices[i] += addCount;
                    }
                }
            }
            for (int i = indices.length - 1; i >= 0; i--) {
                model.remove(indices[i]);
            }
        }
        indices = null;
        addCount = 0;
        addIndex = -1;
    }
}

public class DropDemo extends JPanel implements ActionListener {
    private JComboBox dropCombo;
    private JList list;

    public DropDemo() {
        super(new GridLayout(2, 1));
        add(createArea());
        add(createList());
    }

    private JPanel createList() {
        DefaultListModel listModel = new DefaultListModel();

        for (int i = 0; i < 10; i++) {
            listModel.addElement("List Item " + i);
        }

        list = new JList(listModel);
        list.setSelectionMode(ListSelectionModel.SINGLE_INTERVAL_SELECTION);
        JScrollPane scrollPane = new JScrollPane(list);
        scrollPane.setPreferredSize(new Dimension(400, 100));

        list.setDragEnabled(true);
        list.setTransferHandler(new ListTransferHandler());

        dropCombo = new JComboBox(new String[] { "USE_SELECTION", "ON",
                "INSERT", "ON_OR_INSERT" });
        dropCombo.addActionListener(this);
        JPanel dropPanel = new JPanel();
        dropPanel.add(new JLabel("List Drop Mode:"));
        dropPanel.add(dropCombo);

        JPanel panel = new JPanel(new BorderLayout());
        panel.add(scrollPane, BorderLayout.CENTER);
        panel.add(dropPanel, BorderLayout.SOUTH);
        panel.setBorder(BorderFactory.createTitledBorder("List"));
        return panel;
    }

    private JPanel createArea() {
        String text = "Drag from or drop into this area.\nThe default action is MOVE;\nhold the Control key to COPY.";

        JTextArea area = new JTextArea();
        area.setText(text);
        area.setDragEnabled(true);
        JScrollPane scrollPane = new JScrollPane(area);
        scrollPane.setPreferredSize(new Dimension(400, 100));
        JPanel panel = new JPanel(new BorderLayout());
        panel.add(scrollPane, BorderLayout.CENTER);
        panel.setBorder(BorderFactory.createTitledBorder("Text Area"));
        return panel;
    }

    public void actionPerformed(ActionEvent ae) {
        Object val = dropCombo.getSelectedItem();
        if (val == "USE_SELECTION") {
            list.setDropMode(DropMode.USE_SELECTION);
        } else if (val == "ON") {
            list.setDropMode(DropMode.ON);
        } else if (val == "INSERT") {
            list.setDropMode(DropMode.INSERT);
        } else if (val == "ON_OR_INSERT") {
            list.setDropMode(DropMode.ON_OR_INSERT);
        }
    }

    /**
     * Create the GUI and show it.  For thread safety,
     * this method should be invoked from the
     * event-dispatching thread.
     */
    private static void createAndShowGUI() {
        //Create and set up the window.
        JFrame frame = new JFrame("DropDemo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        //Create and set up the content pane.
        JComponent newContentPane = new DropDemo();
        newContentPane.setOpaque(true); //content panes must be opaque
        frame.setContentPane(newContentPane);

        //Display the window.
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        //Schedule a job for the event-dispatching thread:
        //creating and showing this application's GUI.
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                //Turn off metal's use of bold fonts
                UIManager.put("swing.boldMetal", Boolean.FALSE);
                createAndShowGUI();
            }
        });
    }
}

/*
 * Copyright (c) 1995, 2008, Oracle and/or its affiliates. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 *   - Neither the name of Oracle or the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
Extend TransferHandler to handle drag and drop event - Java Swing

Description

Demo Code

Related Tutorials
