Panel Drop Target
/*
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);
}
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