Implement Drag and Drop in Your Web Apps

package com.gwtsolutions.components.client.ui.dnd;

import com.google.gwt.user.client.ui.AbsolutePanel;
import com.google.gwt.user.client.ui.MouseListener;
import com.google.gwt.user.client.ui.Widget;
import com.gwtsolutions.components.client.ui.MousePanel;
import com.gwtsolutions.components.client.ui.Point;

public abstract class DragSource extends MousePanel {
 private static final String BAD_PARENT =
 "Drag sources must have a parent of type AbsolutePanel";
 private static final MouseListener defaultDragger =
 new FollowsMouseDragger();

private boolean dragging = false;
 private Point originalLocation = null;
 private DropTarget enclosingDropTarget = null;

public DragSource(Widget w) {
 // Drag sources contain only one widget, which is
 // the widget passed to this constructor
 add(w);

// Listener order is significant. See the text
 // of GWT Solutions for more information
 addMouseListener(new DragSourceListener());
 addMouseListener(getMouseListener());
 }

public void onLoad() {
 // GWT calls this method when the drag source's
 // DOM element is added to the browser's DOM tree.
 if ( ! (getParent() instanceof AbsolutePanel))
 throw new IllegalStateException(BAD_PARENT);
 }

public void dragStarted() {
 // subclasses can override this no-op method
 // as needed
 }

public void droppedOutsideDropTarget() {
 // By default, when a drag source is dropped outside
 // of any drop target, it is returned to its original
 // position. Subclasses can override this method to
 // change or augment that behavior
 returnToOriginalPosition();
 }

public void acceptedByDropTarget(DropTarget dt) {
 // subclasses can override this no-op method
 // as needed
 }

public void rejectedByDropTarget(DropTarget dt) {
 // By default, when a drag source is rejected by
 // a drop target, it is returned to its original
 // position. Subclasses can override this method to
 // change or augment that behavior
 returnToOriginalPosition();
 }

public boolean isDragging() {
 return dragging;
 }

public void setDragging(boolean dragging) {
 this.dragging = dragging;
 }

public void setOriginalLocation(Point originalLocation) {
 this.originalLocation = originalLocation;
 }

public DropTarget getEnclosingDropTarget() {
 return enclosingDropTarget;
 }

public void setEnclosingDropTarget(
 DropTarget enclosingDropTarget) {
 this.enclosingDropTarget = enclosingDropTarget;
 }

protected void returnToOriginalPosition() {
 AbsolutePanel ap = (AbsolutePanel) getParent();
 ap.setWidgetPosition(this, originalLocation.x,
 originalLocation.y);
 }

protected MouseListener getMouseListener() {
 return defaultDragger;
 }
}

Implement Drag and Drop in Your Web Apps: Part 2

Drag and Drop Implementation in a GWT Module

The Module Configuration File

The Abstract Drag Source and Drop Target Classes

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