PanelDropTarget.java Source code

Introduction

Here is the source code for PanelDropTarget.java

Source

/*
Core SWING Advanced Programming 
By Kim Topley
ISBN: 0 13 083292 8       
Publisher: Prentice Hall  
*/

import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.datatransfer.DataFlavor;
import java.awt.datatransfer.Transferable;
import java.awt.datatransfer.UnsupportedFlavorException;
import java.awt.dnd.DnDConstants;
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 java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.io.IOException;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.UIManager;

public class PanelDropTarget implements DropTargetListener {
    public PanelDropTarget(JPanel pane) {
        this.pane = pane;

        // Create the DropTarget and register
        // it with the JPanel.
        dropTarget = new DropTarget(pane, DnDConstants.ACTION_COPY_OR_MOVE, this, true, null);
    }

    // Implementation of the DropTargetListener interface
    public void dragEnter(DropTargetDragEvent dtde) {
        DnDUtils.debugPrintln("dragEnter, drop action = " + DnDUtils.showActions(dtde.getDropAction()));

        // Get the type of object being transferred and determine
        // whether it is appropriate.
        checkTransferType(dtde);

        // Accept or reject the drag.
        acceptOrRejectDrag(dtde);
    }

    public void dragExit(DropTargetEvent dte) {
        DnDUtils.debugPrintln("DropTarget dragExit");
    }

    public void dragOver(DropTargetDragEvent dtde) {
        DnDUtils.debugPrintln("DropTarget dragOver, drop action = " + DnDUtils.showActions(dtde.getDropAction()));

        // Accept or reject the drag
        acceptOrRejectDrag(dtde);
    }

    public void dropActionChanged(DropTargetDragEvent dtde) {
        DnDUtils.debugPrintln(
                "DropTarget dropActionChanged, drop action = " + DnDUtils.showActions(dtde.getDropAction()));

        // Accept or reject the drag
        acceptOrRejectDrag(dtde);
    }

    public void drop(DropTargetDropEvent dtde) {
        DnDUtils.debugPrintln("DropTarget drop, drop action = " + DnDUtils.showActions(dtde.getDropAction()));

        // Check the drop action
        if ((dtde.getDropAction() & DnDConstants.ACTION_COPY_OR_MOVE) != 0) {
            // Accept the drop and get the transfer data
            dtde.acceptDrop(dtde.getDropAction());
            Transferable transferable = dtde.getTransferable();

            try {
                boolean result = dropComponent(transferable);

                dtde.dropComplete(result);
                DnDUtils.debugPrintln("Drop completed, success: " + result);
            } catch (Exception e) {
                DnDUtils.debugPrintln("Exception while handling drop " + e);
                dtde.dropComplete(false);
            }
        } else {
            DnDUtils.debugPrintln("Drop target rejected drop");
            dtde.rejectDrop();
        }
    }

    // Internal methods start here

    protected boolean acceptOrRejectDrag(DropTargetDragEvent dtde) {
        int dropAction = dtde.getDropAction();
        int sourceActions = dtde.getSourceActions();
        boolean acceptedDrag = false;

        DnDUtils.debugPrintln("\tSource actions are " + DnDUtils.showActions(sourceActions) + ", drop action is "
                + DnDUtils.showActions(dropAction));

        // Reject if the object being transferred
        // or the operations available are not acceptable.
        if (!acceptableType || (sourceActions & DnDConstants.ACTION_COPY_OR_MOVE) == 0) {
            DnDUtils.debugPrintln("Drop target rejecting drag");
            dtde.rejectDrag();
        } else if ((dropAction & DnDConstants.ACTION_COPY_OR_MOVE) == 0) {
            // Not offering copy or move - suggest a copy
            DnDUtils.debugPrintln("Drop target offering COPY");
            dtde.acceptDrag(DnDConstants.ACTION_COPY);
            acceptedDrag = true;
        } else {
            // Offering an acceptable operation: accept
            DnDUtils.debugPrintln("Drop target accepting drag");
            dtde.acceptDrag(dropAction);
            acceptedDrag = true;
        }

        return acceptedDrag;
    }

    protected void checkTransferType(DropTargetDragEvent dtde) {
        // Only accept a flavor that returns a Component
        acceptableType = false;
        DataFlavor[] fl = dtde.getCurrentDataFlavors();
        for (int i = 0; i < fl.length; i++) {
            Class dataClass = fl[i].getRepresentationClass();

            if (Component.class.isAssignableFrom(dataClass)) {
                // This flavor returns a Component - accept it.
                targetFlavor = fl[i];
                acceptableType = true;
                break;
            }
        }

        DnDUtils.debugPrintln("File type acceptable - " + acceptableType);
    }

    protected boolean dropComponent(Transferable transferable) throws IOException, UnsupportedFlavorException {
        Object o = transferable.getTransferData(targetFlavor);
        if (o instanceof Component) {
            DnDUtils.debugPrintln("Dragged component class is " + o.getClass().getName());
            pane.add((Component) o);
            pane.validate();
            return true;
        }
        return false;
    }

    public static void main(String[] args) {
        try {
            UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsLookAndFeel");
        } catch (Exception evt) {
        }

        final JFrame f = new JFrame("Component drop target example");

        JPanel pane = new JPanel();

        // Add a drop target to the JPanel
        PanelDropTarget target = new PanelDropTarget(pane);

        f.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent evt) {
                System.exit(0);
            }
        });

        f.getContentPane().add(new JScrollPane(pane), BorderLayout.CENTER);
        f.setSize(500, 400);
        f.setVisible(true);
    }

    protected JPanel pane;

    protected DropTarget dropTarget;

    protected boolean acceptableType; // Indicates whether data is acceptable

    protected DataFlavor targetFlavor; // Flavor to use for transfer
}

class DnDUtils {
    public static String showActions(int action) {
        String actions = "";
        if ((action & (DnDConstants.ACTION_LINK | DnDConstants.ACTION_COPY_OR_MOVE)) == 0) {
            return "None";
        }

        if ((action & DnDConstants.ACTION_COPY) != 0) {
            actions += "Copy ";
        }

        if ((action & DnDConstants.ACTION_MOVE) != 0) {
            actions += "Move ";
        }

        if ((action & DnDConstants.ACTION_LINK) != 0) {
            actions += "Link";
        }

        return actions;
    }

    public static boolean isDebugEnabled() {
        return debugEnabled;
    }

    public static void debugPrintln(String s) {
        if (debugEnabled) {
            System.out.println(s);
        }
    }

    private static boolean debugEnabled = (System.getProperty("DnDExamples.debug") != null);
}