bundles/org.eclipse.swt/Eclipse SWT Drag and Drop/photon/org/eclipse/swt/dnd/DropTarget.java

package org.eclipse.swt.dnd;

/*
 * Copyright (c) 2000, 2002 IBM Corp.  All rights reserved.
 * This file is made available under the terms of the Common Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/cpl-v10.html
 */

import org.eclipse.swt.*;
import org.eclipse.swt.graphics.*;
import org.eclipse.swt.widgets.*;
import org.eclipse.swt.internal.*;
import org.eclipse.swt.internal.photon.*;

/**
 *
 * Class <code>DropTarget</code> defines the target object for a drag and drop transfer.
 *
 * IMPORTANT: This class is <em>not</em> intended to be subclassed.
 *
 * <p>This class identifies the <code>Control</code> over which the user must position the cursor
 * in order to drop the data being transferred.  It also specifies what data types can be dropped on 
 * this control and what operations can be performed.  You may have several DropTragets in an 
 * application but there can only be a one to one mapping between a <code>Control</code> and a <code>DropTarget</code>.
 * The DropTarget can receive data from within the same application or from other applications 
 * (such as text dragged from a text editor like Word).</p>
 *
 * <code><pre>
 *	int operations = DND.DROP_MOVE | DND.DROP_COPY | DND.DROP_LINK;
 *	Transfer[] types = new Transfer[] {TextTransfer.getInstance()};
 *	DropTarget target = new DropTarget(label, operations);
 *	target.setTransfer(types);
 * </code></pre>
 *
 * <p>The application is notified of data being dragged over this control and of when a drop occurs by 
 * implementing the interface <code>DropTargetListener</code> which uses the class 
 * <code>DropTargetEvent</code>.  The application can modify the type of drag being performed 
 * on this Control at any stage of the drag by modifying the <code>event.detail</code> field or the 
 * <code>event.currentDataType</code> field.  When the data is dropped, it is the responsibility of 
 * the application to copy this data for its own purposes.
 *
 * <code><pre>
 *	target.addDropListener (new DropTargetListener() {
 *		public void dragEnter(DropTargetEvent event) {};
 *		public void dragOver(DropTargetEvent event) {};
 *		public void dragLeave(DropTargetEvent event) {};
 *		public void dragOperationChanged(DropTargetEvent event) {};
 *		public void dropAccept(DropTargetEvent event) {}
 *		public void drop(DropTargetEvent event) {
 *			// A drop has occurred, copy over the data
 *			if (event.data == null) { // no data to copy, indicate failure in event.detail
 *				event.detail = DND.DROP_NONE;
 *				return;
 *			}
 *			label.setText ((String) event.data); // data copied to label text
 *		}
 * 	});
 * </pre></code>
 *
 * <dl>
 *	<dt><b>Styles</b> <dd>DND.DROP_NONE, DND.DROP_COPY, DND.DROP_MOVE, DND.DROP_LINK 
 *	<dt><b>Events</b> <dd>DND.DragEnter, DND.DragLeave, DND.DragOver, DND.DragOperationChanged, 
 *                        DND.Drop, DND.DropAccept
 * </dl>
 */
public class DropTarget extends Widget {
	
	private Callback dropProc;
	private Callback transferProc;
	private Callback dragProc;
	
	// info for registering as a droptarget	
	private Control control;
	private Listener controlListener;
	private Transfer[] transferAgents = new Transfer[0];
	
	// info about data being dragged over site
	private TransferData selectedDataType;
	private TransferData[] dataTypes;
	private int dropTransferObject;
	
	private DragUnderEffect effect;
	
/**
 * Creates a new <code>DropTarget</code> to handle dropping on the specified <code>Control</code>.
 * 
 * @param control the <code>Control</code> over which the user positions the cursor to drop data
 *
 * @param style the bitwise OR'ing of allowed operations; this may be a combination of any of 
 *					DND.DROP_NONE, DND.DROP_COPY, DND.DROP_MOVE, DND.DROP_LINK
 *
 * @see DND#DROP_NONE
 * @see DND#DROP_COPY
 * @see DND#DROP_MOVE
 * @see DND#DROP_LINK
 */
public DropTarget(Control control, int style) {

	super (control, checkStyle(style));
	
	this.control = control;
	
	controlListener = new Listener () {
		public void handleEvent (Event event) {
			if (!DropTarget.this.isDisposed()){
				DropTarget.this.dispose();
			}
		}
	};
	control.addListener (SWT.Dispose, controlListener);
	
	this.addListener (SWT.Dispose, new Listener () {
		public void handleEvent (Event event) {
			//onDispose();
		}
	});
	
	if (control instanceof Tree) {
		effect = new TreeDragUnderEffect((Tree)control);
	} else if (control instanceof Table) {
		effect = new TableDragUnderEffect((Table)control);
	} else {
		effect = new NoDragUnderEffect(control);
	}
}
/**	 
 * Adds the listener to receive events.
 *
 * @param listener the listener
 *
 * @exception SWTError 
 *	<ul><li>ERROR_THREAD_INVALID_ACCESS when called from the wrong thread</li>
 * 		<li>ERROR_WIDGET_DISPOSED  when the widget has been disposed</li>
 * 		<li>ERROR_NULL_ARGUMENT when listener is null</li></ul>
 */
public void addDropListener(DropTargetListener listener) {	
	if (listener == null) DND.error (SWT.ERROR_NULL_ARGUMENT);
	DNDListener typedListener = new DNDListener (listener);
	addListener (DND.DragEnter, typedListener);
	addListener (DND.DragLeave, typedListener);
	addListener (DND.DragOver, typedListener);
	addListener (DND.DragOperationChanged, typedListener);
	addListener (DND.Drop, typedListener);
	addListener (DND.DropAccept, typedListener);

}
static int checkStyle (int style) {
	if (style == SWT.NONE) return DND.DROP_MOVE;
	return style;
}


/**
 * Returns the Control which is registered for this DropTarget.  This is the control over which the 
 * user positions the cursor to drop the data.
 *
 * @return the Control which is registered for this DropTarget
 */
public Control getControl () {
	return control;
}
public Display getDisplay () {

	if (control == null) DND.error(SWT.ERROR_WIDGET_DISPOSED);
	return control.getDisplay ();
}
/**
 * Returns the list of data types that can be transferred to this DropTarget.
 *
 * @return the list of data types that can be transferred to this DropTarget
 */
public Transfer[] getTransfer(){
	return transferAgents;
}
public void notifyListeners (int eventType, Event event) {
	Point coordinates = new Point(event.x, event.y);
	coordinates = control.toControl(coordinates);
	if (this.control instanceof Tree) {
		event.item = ((Tree)control).getItem(coordinates);
	}
	if (this.control instanceof Table) {
		event.item = ((Table)control).getItem(coordinates);
	}
	super.notifyListeners(eventType, event);
}

/**	 
 * Removes the listener.
 *
 * @param listener the listener
 *
 * @exception SWTError
 *	<ul><li>ERROR_THREAD_INVALID_ACCESS	when called from the wrong thread</li>
 * 		<li>ERROR_WIDGET_DISPOSED when the widget has been disposed</li>
 * 		<li>ERROR_NULL_ARGUMENT when listener is null</li></ul>
 */
public void removeDropListener(DropTargetListener listener) {	
	if (listener == null) DND.error (SWT.ERROR_NULL_ARGUMENT);
	removeListener (DND.DragEnter, listener);
	removeListener (DND.DragLeave, listener);
	removeListener (DND.DragOver, listener);
	removeListener (DND.DragOperationChanged, listener);
	removeListener (DND.Drop, listener);
	removeListener (DND.DropAccept, listener);
}
/**
 * Specifies the list of data types that can be transferred to this DropTarget.
 *
 * @param transferAgents a list of Transfer objects which define the types of data that can be
 *						 dropped on this target
 */
public void setTransfer(Transfer[] transferAgents){
}


protected void checkSubclass () {
	String name = getClass().getName ();
	String validName = DropTarget.class.getName();
	if (!validName.equals(name)) {
		DND.error (SWT.ERROR_INVALID_SUBCLASS);
	}
}
}