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I'm trying to set up code so that the user can drag from a JTable to a JList, and customize the drag image by using the Java 7 function setDragImage in TransferHandler. I grabbed an example on the java tutorial website where they teach about Drag n Drop, and then added a "setDragImage" code. However it is not working. Please see the code below, and locate the setDragImage() line inside the importData function. Why doesn't this work?
/*
* Copyright (c) 1995, 2008, Oracle and/or its affiliates. All rights reserved.
*
*/
import java.util.*;
import java.awt.*;
import java.awt.event.*;
import java.text.*;
import java.awt.datatransfer.*;
import java.awt.image.BufferedImage;
import javax.swing.*;
import javax.swing.text.*;
import javax.swing.tree.*;
import javax.swing.table.*;
public class BasicDND extends JPanel implements ActionListener {
private static JFrame frame;
private JTextArea textArea;
private JTextField textField;
private JList list;
private JTable table;
private JTree tree;
private JColorChooser colorChooser;
private JCheckBox toggleDnD;
public BasicDND() {
super(new BorderLayout());
JPanel leftPanel = createVerticalBoxPanel();
JPanel rightPanel = createVerticalBoxPanel();
//Create a table model.
DefaultTableModel tm = new DefaultTableModel();
tm.addColumn("Column 0");
tm.addColumn("Column 1");
tm.addColumn("Column 2");
tm.addColumn("Column 3");
tm.addRow(new String[]{"Table 00", "Table 01", "Table 02", "Table 03"});
tm.addRow(new String[]{"Table 10", "Table 11", "Table 12", "Table 13"});
tm.addRow(new String[]{"Table 20", "Table 21", "Table 22", "Table 23"});
tm.addRow(new String[]{"Table 30", "Table 31", "Table 32", "Table 33"});
//LEFT COLUMN
//Use the table model to create a table.
table = new JTable(tm);
leftPanel.add(createPanelForComponent(table, "JTable"));
//Create a color chooser.
colorChooser = new JColorChooser();
leftPanel.add(createPanelForComponent(colorChooser, "JColorChooser"));
//RIGHT COLUMN
//Create a textfield.
textField = new JTextField(30);
textField.setText("Favorite foods:\nPizza, Moussaka, Pot roast");
rightPanel.add(createPanelForComponent(textField, "JTextField"));
//Create a scrolled text area.
textArea = new JTextArea(5, 30);
textArea.setText("Favorite shows:\nBuffy, Alias, Angel");
JScrollPane scrollPane = new JScrollPane(textArea);
rightPanel.add(createPanelForComponent(scrollPane, "JTextArea"));
//Create a list model and a list.
DefaultListModel listModel = new DefaultListModel();
listModel.addElement("Martha Washington");
listModel.addElement("Abigail Adams");
listModel.addElement("Martha Randolph");
listModel.addElement("Dolley Madison");
listModel.addElement("Elizabeth Monroe");
listModel.addElement("Louisa Adams");
listModel.addElement("Emily Donelson");
list = new JList(listModel);
list.setVisibleRowCount(-1);
list.getSelectionModel().setSelectionMode(ListSelectionModel.MULTIPLE_INTERVAL_SELECTION);
list.setTransferHandler(new TransferHandler() {
public Image getDragImage() {
return null;
}
@Override
public boolean canImport(TransferHandler.TransferSupport info) {
// we only import Strings
if (!info.isDataFlavorSupported(DataFlavor.stringFlavor)) {
return false;
}
JList.DropLocation dl = (JList.DropLocation)info.getDropLocation();
if (dl.getIndex() == -1) {
return false;
}
return true;
}
public BufferedImage makeImageFromString(String s) {
int width = 100;
int height = 40;
BufferedImage br = new BufferedImage(width,height,BufferedImage.TYPE_INT_ARGB);
Graphics g = br.getGraphics();
g.drawString(s, 0, 0);
//g.fillRect(0, 0, width, height);
System.out.println("made image from " + s);
return br;
}
@Override
public boolean importData(TransferHandler.TransferSupport info) {
if (!info.isDrop()) {
return false;
}
// Check for String flavor
if (!info.isDataFlavorSupported(DataFlavor.stringFlavor)) {
displayDropLocation("List doesn't accept a drop of this type.");
return false;
}
JList.DropLocation dl = (JList.DropLocation)info.getDropLocation();
DefaultListModel listModel = (DefaultListModel)list.getModel();
int index = dl.getIndex();
boolean insert = dl.isInsert();
// Get the current string under the drop.
String value = (String)listModel.getElementAt(index);
// 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; }
//HERE IS THE CODE TO SET THE DRAG IMAGE
this.setDragImage(makeImageFromString(data));
// Display a dialog with the drop information.
String dropValue = "\"" + data + "\" dropped ";
if (dl.isInsert()) {
if (dl.getIndex() == 0) {
displayDropLocation(dropValue + "at beginning of list");
} else if (dl.getIndex() >= list.getModel().getSize()) {
displayDropLocation(dropValue + "at end of list");
} else {
String value1 = (String)list.getModel().getElementAt(dl.getIndex() - 1);
String value2 = (String)list.getModel().getElementAt(dl.getIndex());
displayDropLocation(dropValue + "between \"" + value1 + "\" and \"" + value2 + "\"");
}
} else {
displayDropLocation(dropValue + "on top of " + "\"" + value + "\"");
}
/** This is commented out for the basicdemo.html tutorial page.
** If you add this code snippet back and delete the
** "return false;" line, the list will accept drops
** of type string.
// Perform the actual import.
if (insert) {
listModel.add(index, data);
} else {
listModel.set(index, data);
}
return true;
*/
return false;
}
@Override
public int getSourceActions(JComponent c) {
return COPY;
}
@Override
protected Transferable createTransferable(JComponent c) {
JList list = (JList)c;
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 new StringSelection(buff.toString());
}
});
list.setDropMode(DropMode.ON_OR_INSERT);
JScrollPane listView = new JScrollPane(list);
listView.setPreferredSize(new Dimension(300, 100));
rightPanel.add(createPanelForComponent(listView, "JList"));
//Create a tree.
DefaultMutableTreeNode rootNode = new DefaultMutableTreeNode("Mia Familia");
DefaultMutableTreeNode sharon = new DefaultMutableTreeNode("Sharon");
rootNode.add(sharon);
DefaultMutableTreeNode maya = new DefaultMutableTreeNode("Maya");
sharon.add(maya);
DefaultMutableTreeNode anya = new DefaultMutableTreeNode("Anya");
sharon.add(anya);
sharon.add(new DefaultMutableTreeNode("Bongo"));
maya.add(new DefaultMutableTreeNode("Muffin"));
anya.add(new DefaultMutableTreeNode("Winky"));
DefaultTreeModel model = new DefaultTreeModel(rootNode);
tree = new JTree(model);
tree.getSelectionModel().setSelectionMode
(TreeSelectionModel.DISCONTIGUOUS_TREE_SELECTION);
JScrollPane treeView = new JScrollPane(tree);
treeView.setPreferredSize(new Dimension(300, 100));
rightPanel.add(createPanelForComponent(treeView, "JTree"));
//Create the toggle button.
toggleDnD = new JCheckBox("Turn on Drag and Drop");
toggleDnD.setActionCommand("toggleDnD");
toggleDnD.addActionListener(this);
JSplitPane splitPane = new JSplitPane(JSplitPane.HORIZONTAL_SPLIT,
leftPanel, rightPanel);
splitPane.setOneTouchExpandable(true);
add(splitPane, BorderLayout.CENTER);
add(toggleDnD, BorderLayout.PAGE_END);
setBorder(BorderFactory.createEmptyBorder(5,5,5,5));
}
protected JPanel createVerticalBoxPanel() {
JPanel p = new JPanel();
p.setLayout(new BoxLayout(p, BoxLayout.PAGE_AXIS));
p.setBorder(BorderFactory.createEmptyBorder(5,5,5,5));
return p;
}
public JPanel createPanelForComponent(JComponent comp,
String title) {
JPanel panel = new JPanel(new BorderLayout());
panel.add(comp, BorderLayout.CENTER);
if (title != null) {
panel.setBorder(BorderFactory.createTitledBorder(title));
}
return panel;
}
private void displayDropLocation(final String string) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
JOptionPane.showMessageDialog(null, string);
}
});
}
public void actionPerformed(ActionEvent e) {
if ("toggleDnD".equals(e.getActionCommand())) {
boolean toggle = toggleDnD.isSelected();
textArea.setDragEnabled(toggle);
textField.setDragEnabled(toggle);
list.setDragEnabled(toggle);
table.setDragEnabled(toggle);
tree.setDragEnabled(toggle);
colorChooser.setDragEnabled(toggle);
}
}
/**
* 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.
frame = new JFrame("BasicDnD");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//Create and set up the content pane.
JComponent newContentPane = new BasicDND();
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();
}
});
}
}
456
//As kleopatra says,
//public Image getDragImage() {
// return null;
//}
public boolean importData(TransferHandler.TransferSupport info) {
//...
//HERE IS THE CODE TO SET THE DRAG IMAGE
//XXX: this.setDragImage(makeImageFromString(data));
//...
}
@Override public int getSourceActions(JComponent c) {
System.out.println("getSourceActions");
this.setDragImage(makeImageFromString(c));
return COPY;
}
FontRenderContext frc = new FontRenderContext(null, true, true);
JPanel p = new JPanel();
public BufferedImage makeImageFromString(JComponent c) {
int width = 100;
int height = 40;
BufferedImage br = new BufferedImage(width,height,BufferedImage.TYPE_INT_ARGB);
Graphics g = br.getGraphics();
g.setColor(Color.RED);
g.fillRect(0, 0, width, height);
//*
JList l = (JList)c;
ListCellRenderer r = l.getCellRenderer();
Component comp = r.getListCellRendererComponent(
l, l.getSelectedValue(), l.getSelectedIndex(), false, false);
SwingUtilities.paintComponent(g, comp, p, 0, 0, width, height);
/*/
String s = "aaaa";
Rectangle rect = c.getFont().getStringBounds(s, frc).getBounds();
int tx = (width - rect.width)/2 - rect.x;
int ty = (height - rect.height)/2 - rect.y;
g.setColor(Color.BLACK);
g.drawString(s, tx, ty);
System.out.println("made image from " + s);
//*/
g.dispose();
return br;
}
Note: TransferHandler#setDragImage(java.awt.Image) (Java Platform SE 7 )
Add SSCCE: How to use TransferHandler#setDragImage(...) method.
import java.util.*;
import java.awt.*;
import java.awt.image.*;
import java.awt.datatransfer.*;
import javax.swing.*;
public class BasicDnD {
private JList list;
public JList makeList() {
DefaultListModel<String> m = new DefaultListModel<>();
m.addElement("Martha Washington");
m.addElement("Abigail Adams");
m.addElement("Martha Randolph");
list = new JList<String>(m);
list.setTransferHandler(new TransferHandler() {
@Override public boolean canImport(TransferHandler.TransferSupport info) {
if (!info.isDataFlavorSupported(DataFlavor.stringFlavor)) {
return false;
}
JList.DropLocation dl = (JList.DropLocation)info.getDropLocation();
if (dl.getIndex() == -1) {
return false;
}
return true;
}
@Override public int getSourceActions(JComponent c) {
setDragImage(makeImageFromString(c));
return COPY;
}
private final JPanel p = new JPanel();
private BufferedImage br;
private int width, height;
private BufferedImage makeImageFromString(JComponent src) {
JList l = (JList)src;
int idx = l.getSelectedIndex();
Rectangle rect = list.getCellBounds(idx,idx);
if(rect==null) return null;
if(br==null || rect.width!=width || rect.height!=height) {
width = rect.width;
height = rect.height;
br = new BufferedImage(width,height,BufferedImage.TYPE_INT_ARGB);
}
Component c = l.getCellRenderer().getListCellRendererComponent(
l, l.getSelectedValue(), idx, false, false);
Graphics g = br.getGraphics();
g.clearRect(0,0,width,height);
SwingUtilities.paintComponent(g, c, p, 0, 0, width, height);
g.dispose();
return br;
}
@Override protected Transferable createTransferable(JComponent c) {
JList list = (JList)c;
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 new StringSelection(buff.toString());
}
});
list.setDropMode(DropMode.ON_OR_INSERT);
list.setDragEnabled(true);
return list;
}
public JComponent makeUI() {
JPanel panel = new JPanel(new GridLayout(2,1));
JTextArea textArea = new JTextArea("Drag here from JList!");
panel.add(new JScrollPane(textArea));
panel.add(new JScrollPane(makeList()));
return panel;
}
private static void createAndShowGUI() {
JFrame f = new JFrame("BasicDnD");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setContentPane(new BasicDnD().makeUI());
f.setSize(320, 320);
f.setLocationRelativeTo(null);
f.setVisible(true);
}
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
@Override public void run() { createAndShowGUI(); }
});
}
}
In order to have a TransferHandler display a custom image (when a drag occurs), you must create a subclass of TransferHandler with the following functions overridden by it:
public int getSourceActions(JComponent) - it must return the actions supported by the source (the JComponent from which the drag initiated), if the action requested by the drag when initiated (see 5) doesnt match, it will not work.public Transferable createTransferable(JComponent c) - the TransferHandler must return a Transferable object, if null is returned, the drag will not be initiated.public Image getDragImage() needs to reutn the wanted image, or setDragImage() should be called on an instance of the custom TransferHandlerTo start the drag, override/extend a MouseMotionListener with:
public void mouseDragged(MouseEvent e){
JComponent jc = (JComponent)e.getSource();
jc.getTransferHandler().exportAsDrag(jc, e,TransferHandler.COPY);
}
And also set the JComponent TransferHandler and MouseMotionListener with:
myJComponent.setTransferHandler(new myCustomTransferHandler());
myJComponent.addMouseMotionListener(new myCustomMouseMotionListener());
package test;
import javax.swing.*;
import java.awt.*;
import java.awt.datatransfer.*;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;
import javax.imageio.ImageIO;
public class DragTest{
Image dragImage;
public static void main(String[] args){
new DragTest();
}
public DragTest(){
try{
dragImage = javax.imageio.ImageIO.read( new java.net.URL(
"https://www.icon2s.com/wp-content/uploads/2013/07/black-white-metro-file-icon.png"));
//dragImage = ImageIO.read(new java.io.File("icon.png")); //can be used to read image from file
}catch(java.io.IOException e1){
e1.printStackTrace();
return;
}
dragImage = dragImage.getScaledInstance(64, 64, Image.SCALE_DEFAULT); //scaling the image
JFrame frame = new JFrame();
frame.setLayout(null);
frame.setSize(500,500); frame.setLocationRelativeTo(null); //size and location
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
MyJComponent myJC = new MyJComponent();
myJC.setBounds(50,50,100,100);
myJC.addMouseMotionListener(new MouseMotionListener(){
@Override
public void mouseDragged(MouseEvent e){
JComponent src = (JComponent)e.getSource();
src.getTransferHandler().exportAsDrag(src, e, TransferHandler.COPY); //try to export with the copy action - TransferHandler should support copy
}
@Override
public void mouseMoved(MouseEvent e){}
});
myJC.setTransferHandler(new TransferHandler(){
@Override public Image getDragImage(){ return(dragImage);}
@Override public int getSourceActions(JComponent c){
return(COPY_OR_MOVE); //supporting both copy and move
}
@Override public Transferable createTransferable(JComponent c){
return(new Transferable(){
@Override
public boolean isDataFlavorSupported(DataFlavor flavor){
return false;
}
@Override
public DataFlavor[] getTransferDataFlavors(){
return null;
}
@Override
public Object getTransferData(DataFlavor flavor) throws UnsupportedFlavorException, java.io.IOException {
return null;
}
});
}
});
frame.add(myJC);
frame.setVisible(true);
}
private class MyJComponent extends JComponent{
@Override
public void paintComponent(Graphics g){
g.setColor(Color.RED);
g.fillRect(0, 0, getWidth(), getHeight());
}
}
}
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