Drag and drop
/*
* Copyright (c) 2000 David Flanagan. All rights reserved.
* This code is from the book Java Examples in a Nutshell, 2nd Edition.
* It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or implied.
* You may study, use, and modify it for any non-commercial purpose.
* You may distribute it non-commercially as long as you retain this notice.
* For a commercial use license, or to purchase the book (recommended),
* visit http://www.davidflanagan.com/javaexamples2.
*/
import java.awt.BasicStroke;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Cursor;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.Shape;
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.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 java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.awt.geom.AffineTransform;
import java.awt.geom.PathIterator;
import java.awt.geom.Point2D;
import java.awt.geom.Rectangle2D;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.StringTokenizer;
import javax.swing.ButtonGroup;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JToggleButton;
import javax.swing.JToolBar;
import javax.swing.border.BevelBorder;
import javax.swing.border.Border;
/**
* This component can operate in two modes. In "draw mode", it allows the user
* to scribble with the mouse. In "drag mode", it allows the user to drag
* scribbles with the mouse. Regardless of the mode, it always allows scribbles
* to be dropped on it from other applications.
*/
public class ScribbleDragAndDrop extends JComponent implements
DragGestureListener, // For recognizing the start of drags
DragSourceListener, // For processing drag source events
DropTargetListener, // For processing drop target events
MouseListener, // For processing mouse clicks
MouseMotionListener // For processing mouse drags
{
ArrayList scribbles = new ArrayList(); // A list of Scribbles to draw
Scribble currentScribble; // The scribble in progress
Scribble beingDragged; // The scribble being dragged
DragSource dragSource; // A central DnD object
boolean dragMode; // Are we dragging or scribbling?
// These are some constants we use
static final int LINEWIDTH = 3;
static final BasicStroke linestyle = new BasicStroke(LINEWIDTH);
static final Border normalBorder = new BevelBorder(BevelBorder.LOWERED);
static final Border dropBorder = new BevelBorder(BevelBorder.RAISED);
/** The constructor: set up drag-and-drop stuff */
public ScribbleDragAndDrop() {
// Give ourselves a nice default border.
// We'll change this border during drag-and-drop.
setBorder(normalBorder);
// Register listeners to handle drawing
addMouseListener(this);
addMouseMotionListener(this);
// Create a DragSource and DragGestureRecognizer to listen for drags
// The DragGestureRecognizer will notify the DragGestureListener
// when the user tries to drag an object
dragSource = DragSource.getDefaultDragSource();
dragSource.createDefaultDragGestureRecognizer(this, // What component
DnDConstants.ACTION_COPY_OR_MOVE, // What drag types?
this);// the listener
// Create and set up a DropTarget that will listen for drags and
// drops over this component, and will notify the DropTargetListener
DropTarget dropTarget = new DropTarget(this, // component to monitor
this); // listener to notify
this.setDropTarget(dropTarget); // Tell the component about it.
}
/**
* The component draws itself by drawing each of the Scribble objects.
*/
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.setStroke(linestyle); // Specify wide lines
int numScribbles = scribbles.size();
for (int i = 0; i < numScribbles; i++) {
Scribble s = (Scribble) scribbles.get(i);
g2.draw(s); // Draw the scribble
}
}
public void setDragMode(boolean dragMode) {
this.dragMode = dragMode;
}
public boolean getDragMode() {
return dragMode;
}
/**
* This method, and the following four methods are from the MouseListener
* interface. If we're in drawing mode, this method handles mouse down
* events and starts a new scribble.
*/
public void mousePressed(MouseEvent e) {
if (dragMode)
return;
currentScribble = new Scribble();
scribbles.add(currentScribble);
currentScribble.moveto(e.getX(), e.getY());
}
public void mouseReleased(MouseEvent e) {
}
public void mouseClicked(MouseEvent e) {
}
public void mouseEntered(MouseEvent e) {
}
public void mouseExited(MouseEvent e) {
}
/**
* This method and mouseMoved() below are from the MouseMotionListener
* interface. If we're in drawing mode, this method adds a new point to the
* current scribble and requests a redraw
*/
public void mouseDragged(MouseEvent e) {
if (dragMode)
return;
currentScribble.lineto(e.getX(), e.getY());
repaint();
}
public void mouseMoved(MouseEvent e) {
}
/**
* This method implements the DragGestureListener interface. It will be
* invoked when the DragGestureRecognizer thinks that the user has initiated
* a drag. If we're not in drawing mode, then this method will try to figure
* out which Scribble object is being dragged, and will initiate a drag on
* that object.
*/
public void dragGestureRecognized(DragGestureEvent e) {
// Don't drag if we're not in drag mode
if (!dragMode)
return;
// Figure out where the drag started
MouseEvent inputEvent = (MouseEvent) e.getTriggerEvent();
int x = inputEvent.getX();
int y = inputEvent.getY();
// Figure out which scribble was clicked on, if any by creating a
// small rectangle around the point and testing for intersection.
Rectangle r = new Rectangle(x - LINEWIDTH, y - LINEWIDTH,
LINEWIDTH * 2, LINEWIDTH * 2);
int numScribbles = scribbles.size();
for (int i = 0; i < numScribbles; i++) { // Loop through the scribbles
Scribble s = (Scribble) scribbles.get(i);
if (s.intersects(r)) {
// The user started the drag on top of this scribble, so
// start to drag it.
// First, remember which scribble is being dragged, so we can
// delete it later (if this is a move rather than a copy)
beingDragged = s;
// Next, create a copy that will be the one dragged
Scribble dragScribble = (Scribble) s.clone();
// Adjust the origin to the point the user clicked on.
dragScribble.translate(-x, -y);
// Choose a cursor based on the type of drag the user initiated
Cursor cursor;
switch (e.getDragAction()) {
case DnDConstants.ACTION_COPY:
cursor = DragSource.DefaultCopyDrop;
break;
case DnDConstants.ACTION_MOVE:
cursor = DragSource.DefaultMoveDrop;
break;
default:
return; // We only support move and copys
}
// Some systems allow us to drag an image along with the
// cursor. If so, create an image of the scribble to drag
if (dragSource.isDragImageSupported()) {
Rectangle scribbleBox = dragScribble.getBounds();
Image dragImage = this.createImage(scribbleBox.width,
scribbleBox.height);
Graphics2D g = (Graphics2D) dragImage.getGraphics();
g.setColor(new Color(0, 0, 0, 0)); // transparent background
g.fillRect(0, 0, scribbleBox.width, scribbleBox.height);
g.setColor(Color.black);
g.setStroke(linestyle);
g.translate(-scribbleBox.x, -scribbleBox.y);
g.draw(dragScribble);
Point hotspot = new Point(-scribbleBox.x, -scribbleBox.y);
// Now start dragging, using the image.
e.startDrag(cursor, dragImage, hotspot, dragScribble, this);
} else {
// Or start the drag without an image
e.startDrag(cursor, dragScribble, this);
}
// After we've started dragging one scribble, stop looking
return;
}
}
}
/**
* This method, and the four unused methods that follow it implement the
* DragSourceListener interface. dragDropEnd() is invoked when the user
* drops the scribble she was dragging. If the drop was successful, and if
* the user did a "move" rather than a "copy", then we delete the dragged
* scribble from the list of scribbles to draw.
*/
public void dragDropEnd(DragSourceDropEvent e) {
if (!e.getDropSuccess())
return;
int action = e.getDropAction();
if (action == DnDConstants.ACTION_MOVE) {
scribbles.remove(beingDragged);
beingDragged = null;
repaint();
}
}
// These methods are also part of DragSourceListener.
// They are invoked at interesting points during the drag, and can be
// used to perform "drag over" effects, such as changing the drag cursor
// or drag image.
public void dragEnter(DragSourceDragEvent e) {
}
public void dragExit(DragSourceEvent e) {
}
public void dropActionChanged(DragSourceDragEvent e) {
}
public void dragOver(DragSourceDragEvent e) {
}
// The next five methods implement DropTargetListener
/**
* This method is invoked when the user first drags something over us. If we
* understand the data type being dragged, then call acceptDrag() to tell
* the system that we're receptive. Also, we change our border as a "drag
* under" effect to signal that we can accept the drop.
*/
public void dragEnter(DropTargetDragEvent e) {
if (e.isDataFlavorSupported(Scribble.scribbleDataFlavor)
|| e.isDataFlavorSupported(DataFlavor.stringFlavor)) {
e.acceptDrag(DnDConstants.ACTION_COPY_OR_MOVE);
this.setBorder(dropBorder);
}
}
/** The user is no longer dragging over us, so restore the border */
public void dragExit(DropTargetEvent e) {
this.setBorder(normalBorder);
}
/**
* This is the key method of DropTargetListener. It is invoked when the user
* drops something on us.
*/
public void drop(DropTargetDropEvent e) {
this.setBorder(normalBorder); // Restore the default border
// First, check whether we understand the data that was dropped.
// If we supports our data flavors, accept the drop, otherwise reject.
if (e.isDataFlavorSupported(Scribble.scribbleDataFlavor)
|| e.isDataFlavorSupported(DataFlavor.stringFlavor)) {
e.acceptDrop(DnDConstants.ACTION_COPY_OR_MOVE);
} else {
e.rejectDrop();
return;
}
// We've accepted the drop, so now we attempt to get the dropped data
// from the Transferable object.
Transferable t = e.getTransferable(); // Holds the dropped data
Scribble droppedScribble; // This will hold the Scribble object
// First, try to get the data directly as a scribble object
try {
droppedScribble = (Scribble) t
.getTransferData(Scribble.scribbleDataFlavor);
} catch (Exception ex) { // unsupported flavor, IO exception, etc.
// If that doesn't work, try to get it as a String and parse it
try {
String s = (String) t.getTransferData(DataFlavor.stringFlavor);
droppedScribble = Scribble.parse(s);
} catch (Exception ex2) {
// If we still couldn't get the data, tell the system we failed
e.dropComplete(false);
return;
}
}
// If we get here, we've got the Scribble object
Point p = e.getLocation(); // Where did the drop happen?
droppedScribble.translate(p.getX(), p.getY()); // Move it there
scribbles.add(droppedScribble); // add to display list
repaint(); // ask for redraw
e.dropComplete(true); // signal success!
}
// These are unused DropTargetListener methods
public void dragOver(DropTargetDragEvent e) {
}
public void dropActionChanged(DropTargetDragEvent e) {
}
/**
* The main method. Creates a simple application using this class. Note the
* buttons for switching between draw mode and drag mode.
*/
public static void main(String[] args) {
// Create a frame and put a scribble pane in it
JFrame frame = new JFrame("ScribbleDragAndDrop");
final ScribbleDragAndDrop scribblePane = new ScribbleDragAndDrop();
frame.getContentPane().add(scribblePane, BorderLayout.CENTER);
// Create two buttons for switching modes
JToolBar toolbar = new JToolBar();
ButtonGroup group = new ButtonGroup();
JToggleButton draw = new JToggleButton("Draw");
JToggleButton drag = new JToggleButton("Drag");
draw.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
scribblePane.setDragMode(false);
}
});
drag.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
scribblePane.setDragMode(true);
}
});
group.add(draw);
group.add(drag);
toolbar.add(draw);
toolbar.add(drag);
frame.getContentPane().add(toolbar, BorderLayout.NORTH);
// Start off in drawing mode
draw.setSelected(true);
scribblePane.setDragMode(false);
// Pop up the window
frame.setSize(400, 400);
frame.setVisible(true);
}
}
class Scribble implements Shape, Transferable, Serializable, Cloneable {
protected double[] points = new double[64]; // The scribble data
protected int numPoints = 0; // The current number of points
double maxX = Double.NEGATIVE_INFINITY; // The bounding box
double maxY = Double.NEGATIVE_INFINITY;
double minX = Double.POSITIVE_INFINITY;
double minY = Double.POSITIVE_INFINITY;
/**
* Begin a new polyline at (x,y). Note the use of Double.NaN in the points
* array to mark the beginning of a new polyline
*/
public void moveto(double x, double y) {
if (numPoints + 3 > points.length)
reallocate();
// Mark this as the beginning of a new line
points[numPoints++] = Double.NaN;
// The rest of this method is just like lineto();
lineto(x, y);
}
/**
* Add the point (x,y) to the end of the current polyline
*/
public void lineto(double x, double y) {
if (numPoints + 2 > points.length)
reallocate();
points[numPoints++] = x;
points[numPoints++] = y;
// See if the point enlarges our bounding box
if (x > maxX)
maxX = x;
if (x < minX)
minX = x;
if (y > maxY)
maxY = y;
if (y < minY)
minY = y;
}
/**
* Append the Scribble s to this Scribble
*/
public void append(Scribble s) {
int n = numPoints + s.numPoints;
double[] newpoints = new double[n];
System.arraycopy(points, 0, newpoints, 0, numPoints);
System.arraycopy(s.points, 0, newpoints, numPoints, s.numPoints);
points = newpoints;
numPoints = n;
minX = Math.min(minX, s.minX);
maxX = Math.max(maxX, s.maxX);
minY = Math.min(minY, s.minY);
maxY = Math.max(maxY, s.maxY);
}
/**
* Translate the coordinates of all points in the Scribble by x,y
*/
public void translate(double x, double y) {
for (int i = 0; i < numPoints; i++) {
if (Double.isNaN(points[i]))
continue;
points[i++] += x;
points[i] += y;
}
minX += x;
maxX += x;
minY += y;
maxY += y;
}
/** An internal method to make more room in the data array */
protected void reallocate() {
double[] newpoints = new double[points.length * 2];
System.arraycopy(points, 0, newpoints, 0, numPoints);
points = newpoints;
}
/** Clone a Scribble object and its internal array of data */
public Object clone() {
try {
Scribble s = (Scribble) super.clone(); // make a copy of all fields
s.points = (double[]) points.clone(); // copy the entire array
return s;
} catch (CloneNotSupportedException e) { // This should never happen
return this;
}
}
/** Convert the scribble data to a textual format */
public String toString() {
StringBuffer b = new StringBuffer();
for (int i = 0; i < numPoints; i++) {
if (Double.isNaN(points[i])) {
b.append("m ");
} else {
b.append(points[i]);
b.append(' ');
}
}
return b.toString();
}
/**
* Create a new Scribble object and initialize it by parsing a string of
* coordinate data in the format produced by toString()
*/
public static Scribble parse(String s) throws NumberFormatException {
StringTokenizer st = new StringTokenizer(s);
Scribble scribble = new Scribble();
while (st.hasMoreTokens()) {
String t = st.nextToken();
if (t.charAt(0) == 'm') {
scribble.moveto(Double.parseDouble(st.nextToken()), Double
.parseDouble(st.nextToken()));
} else {
scribble.lineto(Double.parseDouble(t), Double.parseDouble(st
.nextToken()));
}
}
return scribble;
}
// ========= The following methods implement the Shape interface ========
/** Return the bounding box of the Shape */
public Rectangle getBounds() {
return new Rectangle((int) (minX - 0.5f), (int) (minY - 0.5f),
(int) (maxX - minX + 0.5f), (int) (maxY - minY + 0.5f));
}
/** Return the bounding box of the Shape */
public Rectangle2D getBounds2D() {
return new Rectangle2D.Double(minX, minY, maxX - minX, maxY - minY);
}
/** Our shape is an open curve, so it never contains anything */
public boolean contains(Point2D p) {
return false;
}
public boolean contains(Rectangle2D r) {
return false;
}
public boolean contains(double x, double y) {
return false;
}
public boolean contains(double x, double y, double w, double h) {
return false;
}
/**
* Determine if the scribble intersects the specified rectangle by testing
* each line segment individually
*/
public boolean intersects(Rectangle2D r) {
if (numPoints < 4)
return false;
int i = 0;
double x1, y1, x2 = 0.0, y2 = 0.0;
while (i < numPoints) {
if (Double.isNaN(points[i])) { // If we're beginning a new line
i++; // Skip the NaN
x2 = points[i++];
y2 = points[i++];
} else {
x1 = x2;
y1 = y2;
x2 = points[i++];
y2 = points[i++];
if (r.intersectsLine(x1, y1, x2, y2))
return true;
}
}
return false;
}
/** Test for intersection by invoking the method above */
public boolean intersects(double x, double y, double w, double h) {
return intersects(new Rectangle2D.Double(x, y, w, h));
}
/**
* Return a PathIterator object that tells Java2D how to draw this scribble
*/
public PathIterator getPathIterator(AffineTransform at) {
return new ScribbleIterator(at);
}
/**
* Return a PathIterator that doesn't include curves. Ours never does.
*/
public PathIterator getPathIterator(AffineTransform at, double flatness) {
return getPathIterator(at);
}
/**
* This inner class implements the PathIterator interface to describe the
* shape of a scribble. Since a Scribble is composed of arbitrary movetos
* and linetos, we simply return their coordinates
*/
public class ScribbleIterator implements PathIterator {
protected int i = 0; // Position in array
protected AffineTransform transform;
public ScribbleIterator(AffineTransform transform) {
this.transform = transform;
}
/** How to determine insideness and outsideness for this shape */
public int getWindingRule() {
return PathIterator.WIND_NON_ZERO;
}
/** Have we reached the end of the scribble path yet? */
public boolean isDone() {
return i >= numPoints;
}
/** Move on to the next segment of the path */
public void next() {
if (Double.isNaN(points[i]))
i += 3;
else
i += 2;
}
/**
* Get the coordinates of the current moveto or lineto as floats
*/
public int currentSegment(float[] coords) {
int retval;
if (Double.isNaN(points[i])) { // If its a moveto
coords[0] = (float) points[i + 1];
coords[1] = (float) points[i + 2];
retval = SEG_MOVETO;
} else {
coords[0] = (float) points[i];
coords[1] = (float) points[i + 1];
retval = SEG_LINETO;
}
// If a transform was specified, use it on the coordinates
if (transform != null)
transform.transform(coords, 0, coords, 0, 1);
return retval;
}
/**
* Get the coordinates of the current moveto or lineto as doubles
*/
public int currentSegment(double[] coords) {
int retval;
if (Double.isNaN(points[i])) {
coords[0] = points[i + 1];
coords[1] = points[i + 2];
retval = SEG_MOVETO;
} else {
coords[0] = points[i];
coords[1] = points[i + 1];
retval = SEG_LINETO;
}
if (transform != null)
transform.transform(coords, 0, coords, 0, 1);
return retval;
}
}
//====== The following methods implement the Transferable interface =====
// This is the custom DataFlavor for Scribble objects
public static DataFlavor scribbleDataFlavor = new DataFlavor(
Scribble.class, "Scribble");
// This is a list of the flavors we know how to work with
public static DataFlavor[] supportedFlavors = { scribbleDataFlavor,
DataFlavor.stringFlavor };
/** Return the data formats or "flavors" we know how to transfer */
public DataFlavor[] getTransferDataFlavors() {
return (DataFlavor[]) supportedFlavors.clone();
}
/** Check whether we support a given flavor */
public boolean isDataFlavorSupported(DataFlavor flavor) {
return (flavor.equals(scribbleDataFlavor) || flavor
.equals(DataFlavor.stringFlavor));
}
/**
* Return the scribble data in the requested format, or throw an exception
* if we don't support the requested format
*/
public Object getTransferData(DataFlavor flavor)
throws UnsupportedFlavorException {
if (flavor.equals(scribbleDataFlavor)) {
return this;
} else if (flavor.equals(DataFlavor.stringFlavor)) {
return toString();
} else
throw new UnsupportedFlavorException(flavor);
}
}
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