Issue
I had created a frame and then panels in it. I had placed an image in one panel, now I need to drag that image to another panel. How could I do that. Please explain step by step as am a beginner.
Solution
Quick example using pure java, DragGestureListener, DropTargetAdapter and TransferHandler for DnD support of images on one panel to another:
Before any shape is clicked and dragged:
after green shape is selected and dragged onto the empty panel above:
import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.Point;
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.DragSource;
import java.awt.dnd.DropTarget;
import java.awt.dnd.DropTargetAdapter;
import java.awt.dnd.DropTargetDropEvent;
import java.io.IOException;
import java.net.URL;
import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.TransferHandler;
import javax.swing.TransferHandler.TransferSupport;
import javax.swing.border.TitledBorder;
public class Test {
public static void main(String[] args) {
createAndShowJFrame();
}
public static void createAndShowJFrame() {
SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
JFrame frame = createJFrame();
frame.setVisible(true);
}
});
}
private static JFrame createJFrame() {
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.setTitle("Test");
JPanel panel = createEmptyJPanel();
new MyDropTargetListener(panel);//this must be done or we wont be able to drop any image onto the empty panel
frame.add(panel, BorderLayout.CENTER);
try {
frame.add(createJLabelPanel(), BorderLayout.SOUTH);
} catch (Exception ex) {
ex.printStackTrace();
}
frame.pack();
return frame;
}
private static JPanel createEmptyJPanel() {
final JPanel p = new JPanel() {
@Override
public Dimension getPreferredSize() {
return new Dimension(300, 300);
}
};
p.setBorder(new TitledBorder("Drag Image onto this panel"));
TransferHandler dnd = new TransferHandler() {
@Override
public boolean canImport(TransferSupport support) {
if (!support.isDrop()) {
return false;
}
//only Strings
if (!support.isDataFlavorSupported(DataFlavor.imageFlavor)) {
return false;
}
return true;
}
@Override
public boolean importData(TransferSupport support) {
if (!canImport(support)) {
return false;
}
Transferable tansferable = support.getTransferable();
Icon ico;
try {
ico = (Icon) tansferable.getTransferData(DataFlavor.imageFlavor);
} catch (Exception e) {
e.printStackTrace();
return false;
}
p.add(new JLabel(ico));
return true;
}
};
p.setTransferHandler(dnd);
return p;
}
private static JPanel createJLabelPanel() throws Exception {
JPanel panel = new JPanel();
panel.setBorder(new TitledBorder("Drag Image from here to Panel above"));
JLabel label1 = new JLabel(new ImageIcon(new URL("http://i.stack.imgur.com/gJmeJ.png")));
JLabel label2 = new JLabel(new ImageIcon(new URL("http://i.stack.imgur.com/8BGfi.png")));
JLabel label3 = new JLabel(new ImageIcon(new URL("http://i.stack.imgur.com/1lgtq.png")));
MyDragGestureListener dlistener = new MyDragGestureListener();
DragSource ds = new DragSource();
ds.createDefaultDragGestureRecognizer(label1, DnDConstants.ACTION_COPY, dlistener);
ds.createDefaultDragGestureRecognizer(label2, DnDConstants.ACTION_COPY, dlistener);
ds.createDefaultDragGestureRecognizer(label3, DnDConstants.ACTION_COPY, dlistener);
panel.add(label1);
panel.add(label2);
panel.add(label3);
return panel;
}
}
class MyDropTargetListener extends DropTargetAdapter {
private DropTarget dropTarget;
private JPanel p;
public MyDropTargetListener(JPanel panel) {
p = panel;
dropTarget = new DropTarget(panel, DnDConstants.ACTION_COPY, this, true, null);
}
@Override
public void drop(DropTargetDropEvent event) {
try {
DropTarget test = (DropTarget) event.getSource();
Component ca = (Component) test.getComponent();
Point dropPoint = ca.getMousePosition();
Transferable tr = event.getTransferable();
if (event.isDataFlavorSupported(DataFlavor.imageFlavor)) {
Icon ico = (Icon) tr.getTransferData(DataFlavor.imageFlavor);
if (ico != null) {
p.add(new JLabel(ico));
p.revalidate();
p.repaint();
event.dropComplete(true);
}
} else {
event.rejectDrop();
}
} catch (Exception e) {
e.printStackTrace();
event.rejectDrop();
}
}
}
class MyDragGestureListener implements DragGestureListener {
@Override
public void dragGestureRecognized(DragGestureEvent event) {
JLabel label = (JLabel) event.getComponent();
final Icon ico = label.getIcon();
Transferable transferable = new Transferable() {
@Override
public DataFlavor[] getTransferDataFlavors() {
return new DataFlavor[]{DataFlavor.imageFlavor};
}
@Override
public boolean isDataFlavorSupported(DataFlavor flavor) {
if (!isDataFlavorSupported(flavor)) {
return false;
}
return true;
}
@Override
public Object getTransferData(DataFlavor flavor) throws UnsupportedFlavorException, IOException {
return ico;
}
};
event.startDrag(null, transferable);
}
}
Answered By - David Kroukamp Answer Checked By - Dawn Plyler (PHPFixing Volunteer)
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