DNDList.java Source code

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Here is the source code for DNDList.java

Source

/**
 * This is an example of a component, which serves as a DragSource as 
 * well as Drop Target.
 * To illustrate the concept, JList has been used as a droppable target
 * and a draggable source.
 * Any component can be used instead of a JList.
 * The code also contains debugging messages which can be used for 
 * diagnostics and understanding the flow of events.
 * 
 * @version 1.0
 */

import java.awt.datatransfer.DataFlavor;
import java.awt.datatransfer.StringSelection;
import java.awt.datatransfer.Transferable;
import java.awt.dnd.DnDConstants;
import java.awt.dnd.DragGestureEvent;
import java.awt.dnd.DragGestureListener;
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 javax.swing.DefaultListModel;
import javax.swing.JList;
import javax.swing.ListModel;

public class DNDList extends JList implements DropTargetListener, DragSourceListener, DragGestureListener {

    /**
     * enables this component to be a dropTarget
     */

    DropTarget dropTarget = null;

    /**
     * enables this component to be a Drag Source
     */
    DragSource dragSource = null;

    /**
     * constructor - initializes the DropTarget and DragSource.
     */

    public DNDList(ListModel dataModel) {
        super(dataModel);
        dropTarget = new DropTarget(this, this);
        dragSource = new DragSource();
        dragSource.createDefaultDragGestureRecognizer(this, DnDConstants.ACTION_MOVE, this);
    }

    /**
     * is invoked when you are dragging over the DropSite
     * 
     */

    public void dragEnter(DropTargetDragEvent event) {

        // debug messages for diagnostics
        System.out.println("dragEnter");
        event.acceptDrag(DnDConstants.ACTION_MOVE);
    }

    /**
     * is invoked when you are exit the DropSite without dropping
     * 
     */

    public void dragExit(DropTargetEvent event) {
        System.out.println("dragExit");

    }

    /**
     * is invoked when a drag operation is going on
     * 
     */

    public void dragOver(DropTargetDragEvent event) {
        System.out.println("dragOver");
    }

    /**
     * a drop has occurred
     * 
     */

    public void drop(DropTargetDropEvent event) {

        try {
            Transferable transferable = event.getTransferable();

            // we accept only Strings
            if (transferable.isDataFlavorSupported(DataFlavor.stringFlavor)) {

                event.acceptDrop(DnDConstants.ACTION_MOVE);
                String s = (String) transferable.getTransferData(DataFlavor.stringFlavor);
                addElement(s);
                event.getDropTargetContext().dropComplete(true);
            } else {
                event.rejectDrop();
            }
        } catch (Exception exception) {
            System.err.println("Exception" + exception.getMessage());
            event.rejectDrop();
        }
    }

    /**
     * is invoked if the use modifies the current drop gesture
     * 
     */

    public void dropActionChanged(DropTargetDragEvent event) {
    }

    /**
     * a drag gesture has been initiated
     * 
     */

    public void dragGestureRecognized(DragGestureEvent event) {

        Object selected = getSelectedValue();
        if (selected != null) {
            StringSelection text = new StringSelection(selected.toString());

            // as the name suggests, starts the dragging
            dragSource.startDrag(event, DragSource.DefaultMoveDrop, text, this);
        } else {
            System.out.println("nothing was selected");
        }
    }

    /**
     * this message goes to DragSourceListener, informing it that the dragging
     * has ended
     * 
     */

    public void dragDropEnd(DragSourceDropEvent event) {
        if (event.getDropSuccess()) {
            removeElement();
        }
    }

    /**
     * this message goes to DragSourceListener, informing it that the dragging
     * has entered the DropSite
     * 
     */

    public void dragEnter(DragSourceDragEvent event) {
        System.out.println(" dragEnter");
    }

    /**
     * this message goes to DragSourceListener, informing it that the dragging
     * has exited the DropSite
     * 
     */

    public void dragExit(DragSourceEvent event) {
        System.out.println("dragExit");

    }

    /**
     * this message goes to DragSourceListener, informing it that the dragging is
     * currently ocurring over the DropSite
     * 
     */

    public void dragOver(DragSourceDragEvent event) {
        System.out.println("dragExit");

    }

    /**
     * is invoked when the user changes the dropAction
     * 
     */

    public void dropActionChanged(DragSourceDragEvent event) {
        System.out.println("dropActionChanged");
    }

    /**
     * adds elements to itself
     * 
     */

    public void addElement(Object s) {
        ((DefaultListModel) getModel()).addElement(s.toString());
    }

    /**
     * removes an element from itself
     */

    public void removeElement() {
        ((DefaultListModel) getModel()).removeElement(getSelectedValue());
    }

}