Drop everywhere in a jpanel

Question

Based on this example : https://stackoverflow.com/a/17359895/3259386

I have two panels, one for drag and the other for drop, I just drag a copy and I don't move the dragged image.

the code is...

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("https://i.sstatic.net/gJmeJ.png")));
    JLabel label2 = new JLabel(new ImageIcon(new URL("https://i.sstatic.net/8BGfi.png")));
    JLabel label3 = new JLabel(new ImageIcon(new URL("https://i.sstatic.net/1lgtq.png")));

    MyDragGestureListener dlistener = new MyDragGestureListener();
    DragSource ds1 = new DragSource();
    ds1.createDefaultDragGestureRecognizer(label1, DnDConstants.ACTION_COPY, dlistener);

    DragSource ds2 = new DragSource();
    ds2.createDefaultDragGestureRecognizer(label2, DnDConstants.ACTION_COPY, dlistener);

    DragSource ds3 = new DragSource();
    ds3.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);
}
}

when I drop the element on the top panel, the element is placed in the center like this

I want to drop everywhere on the top panel.

When I set the top panel to null layout like this : p.setLayout(null);, the dropped image don't show anymore.

camickr · Accepted Answer

when I drop the element on the top panel, the element is placed in the center like this

The default layout manager for the panel is a FlowLayout.

When I set the top panel to null layout ... the dropped image don't show anymore.

When you use a null layout you are responsible for setting the size and location of the component.

//p.add(new JLabel(ico));
JLabel label = new JLabel(ico);
label.setSize( label.getPreferredSize());
label.setLocation(...);
p.add(label);

You can also use the TransferSupport class to get the DropLocation class which contains the drop point that you can use the set the location of the label.

Drop everywhere in a jpanel

Answers (2)

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