bundles/org.eclipse.swt/Eclipse SWT Drag and Drop/win32/org/eclipse/swt/dnd/DragSource.java

/*******************************************************************************
 * Copyright (c) 2000, 2020 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *     Lars Vogel <Lars.Vogel@vogella.com> - Bug 497807
 *     Paul Pazderski - Improved implementation of IDataObject for bug 549643, 549661 and 567422
 *******************************************************************************/
package org.eclipse.swt.dnd;


import org.eclipse.swt.*;
import org.eclipse.swt.graphics.*;
import org.eclipse.swt.internal.*;
import org.eclipse.swt.internal.ole.win32.*;
import org.eclipse.swt.internal.win32.*;
import org.eclipse.swt.widgets.*;

/**
 *
 * <code>DragSource</code> defines the source object for a drag and drop transfer.
 *
 * <p>IMPORTANT: This class is <em>not</em> intended to be subclassed.</p>
 *
 * <p>A drag source is the object which originates a drag and drop operation. For the specified widget,
 * it defines the type of data that is available for dragging and the set of operations that can
 * be performed on that data.  The operations can be any bit-wise combination of DND.MOVE, DND.COPY or
 * DND.LINK.  The type of data that can be transferred is specified by subclasses of Transfer such as
 * TextTransfer or FileTransfer.  The type of data transferred can be a predefined system type or it
 * can be a type defined by the application.  For instructions on how to define your own transfer type,
 * refer to <code>ByteArrayTransfer</code>.</p>
 *
 * <p>You may have several DragSources in an application but you can only have one DragSource
 * per Control.  Data dragged from this DragSource can be dropped on a site within this application
 * or it can be dropped on another application such as an external Text editor.</p>
 *
 * <p>The application supplies the content of the data being transferred by implementing the
 * <code>DragSourceListener</code> and associating it with the DragSource via DragSource#addDragListener.</p>
 *
 * <p>When a successful move operation occurs, the application is required to take the appropriate
 * action to remove the data from its display and remove any associated operating system resources or
 * internal references.  Typically in a move operation, the drop target makes a copy of the data
 * and the drag source deletes the original.  However, sometimes copying the data can take a long
 * time (such as copying a large file).  Therefore, on some platforms, the drop target may actually
 * move the data in the operating system rather than make a copy.  This is usually only done in
 * file transfers.  In this case, the drag source is informed in the DragEnd event that a
 * DROP_TARGET_MOVE was performed.  It is the responsibility of the drag source at this point to clean
 * up its displayed information.  No action needs to be taken on the operating system resources.</p>
 *
 * <p> The following example shows a Label widget that allows text to be dragged from it.</p>
 *
 * <pre><code>
 *	// Enable a label as a Drag Source
 *	Label label = new Label(shell, SWT.NONE);
 *	// This example will allow text to be dragged
 *	Transfer[] types = new Transfer[] {TextTransfer.getInstance()};
 *	// This example will allow the text to be copied or moved to the drop target
 *	int operations = DND.DROP_MOVE | DND.DROP_COPY;
 *
 *	DragSource source = new DragSource(label, operations);
 *	source.setTransfer(types);
 *	source.addDragListener(new DragSourceListener() {
 *		public void dragStart(DragSourceEvent e) {
 *			// Only start the drag if there is actually text in the
 *			// label - this text will be what is dropped on the target.
 *			if (label.getText().length() == 0) {
 *				event.doit = false;
 *			}
 *		};
 *		public void dragSetData(DragSourceEvent event) {
 *			// A drop has been performed, so provide the data of the
 *			// requested type.
 *			// (Checking the type of the requested data is only
 *			// necessary if the drag source supports more than
 *			// one data type but is shown here as an example).
 *			if (TextTransfer.getInstance().isSupportedType(event.dataType)){
 *				event.data = label.getText();
 *			}
 *		}
 *		public void dragFinished(DragSourceEvent event) {
 *			// A Move operation has been performed so remove the data
 *			// from the source
 *			if (event.detail == DND.DROP_MOVE)
 *				label.setText("");
 *		}
 *	});
 * </code></pre>
 *
 *
 * <dl>
 *	<dt><b>Styles</b></dt> <dd>DND.DROP_NONE, DND.DROP_COPY, DND.DROP_MOVE, DND.DROP_LINK</dd>
 *	<dt><b>Events</b></dt> <dd>DND.DragStart, DND.DragSetData, DND.DragEnd</dd>
 * </dl>
 *
 * @see <a href="http://www.eclipse.org/swt/snippets/#dnd">Drag and Drop snippets</a>
 * @see <a href="http://www.eclipse.org/swt/examples.php">SWT Example: DNDExample</a>
 * @see <a href="http://www.eclipse.org/swt/">Sample code and further information</a>
 * @noextend This class is not intended to be subclassed by clients.
 */
public class DragSource extends Widget {

	// info for registering as a drag source
	Control control;
	Listener controlListener;
	Transfer[] transferAgents = new Transfer[0];
	DragSourceEffect dragEffect;
	Composite topControl;
	long hwndDrag;

	// ole interfaces
	COMIDropSource iDropSource;
	COMIDataObject iDataObject;

	//workaround - track the operation performed by the drop target for DragEnd event
	int dataEffect = DND.DROP_NONE;

	static final String DEFAULT_DRAG_SOURCE_EFFECT = "DEFAULT_DRAG_SOURCE_EFFECT"; //$NON-NLS-1$
	static final int CFSTR_PERFORMEDDROPEFFECT  = Transfer.registerType("Performed DropEffect");	 //$NON-NLS-1$
	static final TCHAR WindowClass = new TCHAR (0, "#32770", true);

	private class COMIDropSource extends COMObject {

		private long refCount = 0;

		/**
		 * Create a new IDropSource COM object. Object is created with one active
		 * reference. (see {@link #Release()})
		 */
		public COMIDropSource() {
			super(new int[]{2, 0, 0, 2, 1});
			AddRef();
		}

		@Override
		public long method0(long[] args) {return QueryInterface(this, args[0], args[1]);}
		@Override
		public long method1(long[] args) {return AddRef();}
		@Override
		public long method2(long[] args) {return Release();}
		@Override
		public long method3(long[] args) {return QueryContinueDrag((int)args[0], (int)args[1]);}
		@Override
		public long method4(long[] args) {return GiveFeedback((int)args[0]);}

		public long AddRef() {
			refCount++;
			return refCount;
		}

		public long Release() {
			refCount--;
			if (refCount == 0) {
				if (DragSource.this.iDropSource == this) {
					DragSource.this.iDropSource = null;
				}
				this.dispose();
				if (COM.FreeUnusedLibraries) {
					COM.CoFreeUnusedLibraries();
				}
			}
			return refCount;
		}
	}

	private class COMIDataObject extends COMObject {
		/*
		 * A SWT application is used to provide the data to drag in an event callback
		 * which is called while the DND operation is performed. However Windows expects
		 * the data to passed around in an object whose lifetime is managed through
		 * reference counting. The drop target can keep a reference on the IDataObject
		 * and even try to query the data long after the DND operation is finished. One
		 * such case is Windows Explorer when showing a Portal Device (see bug 549661).
		 * SWT does two things to support this case:
		 * 1. Implement reference counting as intended. I.e. do not force release the
		 * object after DND is finished but trust that all involved applications are
		 * able to count correctly and will release the object at some point.
		 * 2. Cache the data which was last transfered/generated from the DragSource
		 * to be able to send it again after the DND operation is finished.
		 */

		private long refCount = 0;

		private final Transfer[] transferAgents;

		/**
		 * The most recent data send in a GetData request (or GetDataHere if
		 * implemented). Or from another perspective the data the application returned
		 * in the most recent {@link DND#DragSetData} event.
		 */
		private Object lastData = null;

		/**
		 * Create a new IDataObject COM object. Objects are created with one active
		 * reference. (see {@link #Release()})
		 *
		 * @param transferAgents should be the transfer agents which are set on
		 *                       DragSource at the time this object is created.
		 */
		public COMIDataObject(Transfer[] transferAgents) {
			super(new int[]{2, 0, 0, 2, 2, 1, 2, 3, 2, 4, 1, 1});
			AddRef();
			this.transferAgents = transferAgents;
		}

		@Override
		public long method0(long[] args) {return QueryInterface(this, args[0], args[1]);}
		@Override
		public long method1(long[] args) {return AddRef();}
		@Override
		public long method2(long[] args) {return Release();}
		@Override
		public long method3(long[] args) {return GetData(args[0], args[1]);}
		// method4 GetDataHere - not implemented
		@Override
		public long method5(long[] args) {return QueryGetData(transferAgents, args[0]);}
		// method6 GetCanonicalFormatEtc - not implemented
		@Override
		public long method7(long[] args) {return SetData(args[0], args[1], (int)args[2]);}
		@Override
		public long method8(long[] args) {return EnumFormatEtc(transferAgents, (int)args[0], args[1]);}
		// method9 DAdvise - not implemented
		// method10 DUnadvise - not implemented
		// method11 EnumDAdvise - not implemented

		public long AddRef() {
			refCount++;
			return refCount;
		}

		public long Release() {
			refCount--;
			if (refCount == 0) {
				if (DragSource.this.iDataObject == this) {
					DragSource.this.iDataObject = null;
				}
				this.dispose();
				if (COM.FreeUnusedLibraries) {
					COM.CoFreeUnusedLibraries();
				}
			}
			return refCount;
		}

		/**
		 * Check if this IDataObject is currently used in a DND operation.
		 *
		 * @return <code>true</true> if this object currently used for DND
		 */
		private boolean isActive() {
			return DragSource.this.iDataObject == this;
		}

		private int GetData(long pFormatetc, long pmedium) {
			/* Called by a data consumer to obtain data from a source data object.
			   The GetData method renders the data described in the specified FORMATETC
			   structure and transfers it through the specified STGMEDIUM structure.
			   The caller then assumes responsibility for releasing the STGMEDIUM structure.
			*/
			if (pFormatetc == 0 || pmedium == 0) return COM.E_INVALIDARG;

			if (QueryGetData(transferAgents, pFormatetc) != COM.S_OK) return COM.DV_E_FORMATETC;

			TransferData transferData = new TransferData();
			transferData.formatetc = new FORMATETC();
			COM.MoveMemory(transferData.formatetc, pFormatetc, FORMATETC.sizeof);
			transferData.type = transferData.formatetc.cfFormat;
			transferData.stgmedium = new STGMEDIUM();
			transferData.result = COM.E_FAIL;

			final Object data;
			if (isActive()) {
				DNDEvent event = new DNDEvent();
				event.widget = DragSource.this;
				event.time = OS.GetMessageTime();
				event.dataType = transferData;
				notifyListeners(DND.DragSetData,event);

				if (!event.doit) return COM.E_FAIL;

				lastData = event.data;
				data = event.data;
			} else {
				if (lastData == null) {
					return COM.E_FAIL;
				}
				data = lastData;
			}

			// get matching transfer agent to perform conversion
			Transfer transfer = null;
			for (Transfer transferAgent : transferAgents) {
				if (transferAgent != null && transferAgent.isSupportedType(transferData)){
					transfer = transferAgent;
					break;
				}
			}

			if (transfer == null) return COM.DV_E_FORMATETC;
			transfer.javaToNative(data, transferData);
			if (transferData.result != COM.S_OK) return transferData.result;
			COM.MoveMemory(pmedium, transferData.stgmedium, STGMEDIUM.sizeof);
			return transferData.result;
		}

		private int SetData(long pFormatetc, long pmedium, int fRelease) {
			if (pFormatetc == 0 || pmedium == 0) return COM.E_INVALIDARG;
			FORMATETC formatetc = new FORMATETC();
			COM.MoveMemory(formatetc, pFormatetc, FORMATETC.sizeof);
			if (formatetc.cfFormat == CFSTR_PERFORMEDDROPEFFECT && formatetc.tymed == COM.TYMED_HGLOBAL) {
				STGMEDIUM stgmedium = new STGMEDIUM();
				COM.MoveMemory(stgmedium, pmedium,STGMEDIUM.sizeof);
				//TODO - this should be GlobalLock()
				long[] ptrEffect = new long[1];
				OS.MoveMemory(ptrEffect, stgmedium.unionField, C.PTR_SIZEOF);
				int[] effect = new int[1];
				OS.MoveMemory(effect, ptrEffect[0], 4);
				if (isActive()) {
					dataEffect = osToOp(effect[0]);
				}
			}
			if (fRelease == 1) {
				COM.ReleaseStgMedium(pmedium);
			}
			return COM.S_OK;
		}
	}

/**
 * Creates a new <code>DragSource</code> to handle dragging from the specified <code>Control</code>.
 * Creating an instance of a DragSource may cause system resources to be allocated depending on the platform.
 * It is therefore mandatory that the DragSource instance be disposed when no longer required.
 *
 * @param control the <code>Control</code> that the user clicks on to initiate the drag
 * @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
 *
 * @exception SWTException <ul>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the parent</li>
 *    <li>ERROR_INVALID_SUBCLASS - if this class is not an allowed subclass</li>
 * </ul>
 * @exception SWTError <ul>
 *    <li>ERROR_CANNOT_INIT_DRAG - unable to initiate drag source; this will occur if more than one
 *        drag source is created for a control or if the operating system will not allow the creation
 *        of the drag source</li>
 * </ul>
 *
 * <p>NOTE: ERROR_CANNOT_INIT_DRAG should be an SWTException, since it is a
 * recoverable error, but can not be changed due to backward compatibility.</p>
 *
 * @see Widget#dispose
 * @see DragSource#checkSubclass
 * @see DND#DROP_NONE
 * @see DND#DROP_COPY
 * @see DND#DROP_MOVE
 * @see DND#DROP_LINK
 */
public DragSource(Control control, int style) {
	super(control, checkStyle(style));
	this.control = control;
	if (control.getData(DND.DRAG_SOURCE_KEY) != null) {
		DND.error(DND.ERROR_CANNOT_INIT_DRAG);
	}
	control.setData(DND.DRAG_SOURCE_KEY, this);

	controlListener = event -> {
		if (event.type == SWT.Dispose) {
			if (!DragSource.this.isDisposed()) {
				DragSource.this.dispose();
			}
		}
		if (event.type == SWT.DragDetect) {
			if (!DragSource.this.isDisposed()) {
				DragSource.this.drag(event);
			}
		}
	};
	control.addListener(SWT.Dispose, controlListener);
	control.addListener(SWT.DragDetect, controlListener);

	this.addListener(SWT.Dispose, e -> DragSource.this.onDispose());

	Object effect = control.getData(DEFAULT_DRAG_SOURCE_EFFECT);
	if (effect instanceof DragSourceEffect) {
		dragEffect = (DragSourceEffect) effect;
	} else if (control instanceof Tree) {
		dragEffect = new TreeDragSourceEffect((Tree) control);
	} else if (control instanceof Table) {
		dragEffect = new TableDragSourceEffect((Table) control);
	}
}

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

/**
 * Adds the listener to the collection of listeners who will
 * be notified when a drag and drop operation is in progress, by sending
 * it one of the messages defined in the <code>DragSourceListener</code>
 * interface.
 *
 * <ul>
 * <li><code>dragStart</code> is called when the user has begun the actions required to drag the widget.
 * This event gives the application the chance to decide if a drag should be started.
 * <li><code>dragSetData</code> is called when the data is required from the drag source.
 * <li><code>dragFinished</code> is called when the drop has successfully completed (mouse up
 * over a valid target) or has been terminated (such as hitting the ESC key). Perform cleanup
 * such as removing data from the source side on a successful move operation.
 * </ul>
 *
 * @param listener the listener which should be notified
 *
 * @exception IllegalArgumentException <ul>
 *    <li>ERROR_NULL_ARGUMENT - if the listener is null</li>
 * </ul>
 * @exception SWTException <ul>
 *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
 * </ul>
 *
 * @see DragSourceListener
 * @see #getDragListeners
 * @see #removeDragListener
 * @see DragSourceEvent
 */
public void addDragListener(DragSourceListener listener) {
	if (listener == null) DND.error(SWT.ERROR_NULL_ARGUMENT);
	DNDListener typedListener = new DNDListener(listener);
	typedListener.dndWidget = this;
	addListener(DND.DragStart, typedListener);
	addListener(DND.DragSetData, typedListener);
	addListener(DND.DragEnd, typedListener);
}

private void createCOMInterfaces() {
	releaseCOMInterfaces();
	iDropSource = new COMIDropSource();
	iDataObject = new COMIDataObject(transferAgents);
}

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

private void releaseCOMInterfaces() {
	if (iDropSource != null)
		iDropSource.Release();
	iDropSource = null;

	if (iDataObject != null)
		iDataObject.Release();
	iDataObject = null;
}

private void drag(Event dragEvent) {
	DNDEvent event = new DNDEvent();
	event.widget = this;
	event.x = dragEvent.x;
	event.y = dragEvent.y;
	event.time = OS.GetMessageTime();
	event.doit = true;
	notifyListeners(DND.DragStart,event);
	if (!event.doit || transferAgents == null || transferAgents.length == 0 ) return;

	int[] pdwEffect = new int[1];
	int operations = opToOs(getStyle());
	Display display = control.getDisplay();
	String key = "org.eclipse.swt.internal.win32.runMessagesInIdle"; //$NON-NLS-1$
	Object oldValue = display.getData(key);
	display.setData(key, Boolean.TRUE);
	ImageList imagelist = null;
	Image image = event.image;
	hwndDrag = 0;
	topControl = null;
	if (image != null) {
		imagelist = new ImageList(SWT.NONE);
		imagelist.add(image);
		topControl = control.getShell();
		/*
		 * Bug in Windows. The image is inverted if the shell is RIGHT_TO_LEFT.
		 * The fix is to create a transparent window that covers the shell client
		 * area and use it during the drag to prevent the image from being inverted.
		 * On XP if the shell is RTL, the image is not displayed.
		 */
		int offsetX = event.offsetX;
		hwndDrag = topControl.handle;
		if ((topControl.getStyle() & SWT.RIGHT_TO_LEFT) != 0) {
			offsetX = image.getBoundsInPixels().width - offsetX;
			RECT rect = new RECT ();
			OS.GetClientRect (topControl.handle, rect);
			hwndDrag = OS.CreateWindowEx (
				OS.WS_EX_TRANSPARENT | OS.WS_EX_NOINHERITLAYOUT,
				WindowClass,
				null,
				OS.WS_CHILD | OS.WS_CLIPSIBLINGS,
				0, 0,
				rect.right - rect.left, rect.bottom - rect.top,
				topControl.handle,
				0,
				OS.GetModuleHandle (null),
				null);
			OS.ShowWindow (hwndDrag, OS.SW_SHOW);
		}
		OS.ImageList_BeginDrag(imagelist.getHandle(), 0, offsetX, event.offsetY);
		/*
		* Feature in Windows. When ImageList_DragEnter() is called,
		* it takes a snapshot of the screen  If a drag is started
		* when another window is in front, then the snapshot will
		* contain part of the other window, causing pixel corruption.
		* The fix is to force all paints to be delivered before
		* calling ImageList_DragEnter().
		*/
		int flags = OS.RDW_UPDATENOW | OS.RDW_ALLCHILDREN;
		OS.RedrawWindow (topControl.handle, null, 0, flags);
		POINT pt = new POINT ();
		pt.x = DPIUtil.autoScaleUp(dragEvent.x);// To Pixels
		pt.y = DPIUtil.autoScaleUp(dragEvent.y);// To Pixels
		OS.MapWindowPoints (control.handle, 0, pt, 1);
		RECT rect = new RECT ();
		OS.GetWindowRect (hwndDrag, rect);
		OS.ImageList_DragEnter(hwndDrag, pt.x - rect.left, pt.y - rect.top);
	}
	String externalLoopKey = "org.eclipse.swt.internal.win32.externalEventLoop";
	int result = COM.DRAGDROP_S_CANCEL;
	try {
		createCOMInterfaces();
		display.setData(externalLoopKey, Boolean.TRUE);
		result = COM.DoDragDrop(iDataObject.getAddress(), iDropSource.getAddress(), operations, pdwEffect);
	} finally {
		display.setData(externalLoopKey, Boolean.FALSE);
		// ensure that we don't leave transparent window around
		if (hwndDrag != 0) {
			OS.ImageList_DragLeave(hwndDrag);
			OS.ImageList_EndDrag();
			imagelist.dispose();
			if (hwndDrag != topControl.handle) OS.DestroyWindow(hwndDrag);
			hwndDrag = 0;
			topControl = null;
		}
		display.setData(key, oldValue);
		releaseCOMInterfaces();
	}
	int operation = osToOp(pdwEffect[0]);
	if (dataEffect == DND.DROP_MOVE) {
		operation = (operation == DND.DROP_NONE || operation == DND.DROP_COPY) ? DND.DROP_TARGET_MOVE : DND.DROP_MOVE;
	} else {
		if (dataEffect != DND.DROP_NONE) {
			operation = dataEffect;
		}
	}

	event = new DNDEvent();
	event.widget = this;
	event.time = OS.GetMessageTime();
	event.doit = (result == COM.DRAGDROP_S_DROP);
	event.detail = operation;
	notifyListeners(DND.DragEnd,event);
	dataEffect = DND.DROP_NONE;
}
/*
 * EnumFormatEtc([in] dwDirection, [out] ppenumFormatetc)
 * Ownership of ppenumFormatetc transfers from callee to caller so reference count on ppenumFormatetc
 * must be incremented before returning.  Caller is responsible for releasing ppenumFormatetc.
 */
private static int EnumFormatEtc(Transfer[] transferAgents, int dwDirection, long ppenumFormatetc) {
	// only allow getting of data - SetData is not currently supported
	if (dwDirection == COM.DATADIR_SET) return COM.E_NOTIMPL;

	// what types have been registered?
	TransferData[] allowedDataTypes = new TransferData[0];
	for (Transfer transferAgent : transferAgents) {
		if (transferAgent != null) {
			TransferData[] formats = transferAgent.getSupportedTypes();
			TransferData[] newAllowedDataTypes = new TransferData[allowedDataTypes.length + formats.length];
			System.arraycopy(allowedDataTypes, 0, newAllowedDataTypes, 0, allowedDataTypes.length);
			System.arraycopy(formats, 0, newAllowedDataTypes, allowedDataTypes.length, formats.length);
			allowedDataTypes = newAllowedDataTypes;
		}
	}

	OleEnumFORMATETC enumFORMATETC = new OleEnumFORMATETC();
	enumFORMATETC.AddRef();

	FORMATETC[] formats = new FORMATETC[allowedDataTypes.length];
	for (int i = 0; i < formats.length; i++){
		formats[i] = allowedDataTypes[i].formatetc;
	}
	enumFORMATETC.setFormats(formats);

	OS.MoveMemory(ppenumFormatetc, new long[] {enumFORMATETC.getAddress()}, C.PTR_SIZEOF);
	return COM.S_OK;
}
/**
 * Returns the Control which is registered for this DragSource.  This is the control that the
 * user clicks in to initiate dragging.
 *
 * @return the Control which is registered for this DragSource
 */
public Control getControl() {
	return control;
}

/**
 * Returns an array of listeners who will be notified when a drag and drop
 * operation is in progress, by sending it one of the messages defined in
 * the <code>DragSourceListener</code> interface.
 *
 * @return the listeners who will be notified when a drag and drop
 * operation is in progress
 *
 * @exception SWTException <ul>
 *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
 * </ul>
 *
 * @see DragSourceListener
 * @see #addDragListener
 * @see #removeDragListener
 * @see DragSourceEvent
 *
 * @since 3.4
 */
public DragSourceListener[] getDragListeners() {
	Listener[] listeners = getListeners(DND.DragStart);
	int length = listeners.length;
	DragSourceListener[] dragListeners = new DragSourceListener[length];
	int count = 0;
	for (int i = 0; i < length; i++) {
		Listener listener = listeners[i];
		if (listener instanceof DNDListener) {
			dragListeners[count] = (DragSourceListener) ((DNDListener) listener).getEventListener();
			count++;
		}
	}
	if (count == length) return dragListeners;
	DragSourceListener[] result = new DragSourceListener[count];
	System.arraycopy(dragListeners, 0, result, 0, count);
	return result;
}

/**
 * Returns the drag effect that is registered for this DragSource.  This drag
 * effect will be used during a drag and drop operation.
 *
 * @return the drag effect that is registered for this DragSource
 *
 * @since 3.3
 */
public DragSourceEffect getDragSourceEffect() {
	return dragEffect;
}

/**
 * Returns the list of data types that can be transferred by this DragSource.
 *
 * @return the list of data types that can be transferred by this DragSource
 */
public Transfer[] getTransfer(){
	return transferAgents;
}

private int GiveFeedback(int dwEffect) {
	return COM.DRAGDROP_S_USEDEFAULTCURSORS;
}

private int QueryContinueDrag(int fEscapePressed, int grfKeyState) {
	if (topControl != null && topControl.isDisposed()) return COM.DRAGDROP_S_CANCEL;
	if (fEscapePressed != 0){
		if (hwndDrag != 0) OS.ImageList_DragLeave(hwndDrag);
		return COM.DRAGDROP_S_CANCEL;
	}
	/*
	* Bug in Windows.  On some machines that do not have XBUTTONs,
	* the MK_XBUTTON1 and OS.MK_XBUTTON2 bits are sometimes set,
	* causing mouse capture to become stuck.  The fix is to test
	* for the extra buttons only when they exist.
	*/
	int mask = OS.MK_LBUTTON | OS.MK_MBUTTON | OS.MK_RBUTTON;
//	if (display.xMouse) mask |= OS.MK_XBUTTON1 | OS.MK_XBUTTON2;
	if ((grfKeyState & mask) == 0) {
		if (hwndDrag != 0) OS.ImageList_DragLeave(hwndDrag);
		return COM.DRAGDROP_S_DROP;
	}

	if (hwndDrag != 0) {
		POINT pt = new POINT ();
		OS.GetCursorPos (pt);
		RECT rect = new RECT ();
		OS.GetWindowRect (hwndDrag, rect);
		OS.ImageList_DragMove (pt.x - rect.left, pt.y - rect.top);
	}
	return COM.S_OK;
}

private void onDispose() {
	if (control == null) return;
	releaseCOMInterfaces();
	if (controlListener != null){
		control.removeListener(SWT.Dispose, controlListener);
		control.removeListener(SWT.DragDetect, controlListener);
	}
	controlListener = null;
	control.setData(DND.DRAG_SOURCE_KEY, null);
	control = null;
	transferAgents = null;
}

private int opToOs(int operation) {
	int osOperation = 0;
	if ((operation & DND.DROP_COPY) != 0){
		osOperation |= COM.DROPEFFECT_COPY;
	}
	if ((operation & DND.DROP_LINK) != 0) {
		osOperation |= COM.DROPEFFECT_LINK;
	}
	if ((operation & DND.DROP_MOVE) != 0) {
		osOperation |= COM.DROPEFFECT_MOVE;
	}
	return osOperation;
}

private int osToOp(int osOperation){
	int operation = 0;
	if ((osOperation & COM.DROPEFFECT_COPY) != 0){
		operation |= DND.DROP_COPY;
	}
	if ((osOperation & COM.DROPEFFECT_LINK) != 0) {
		operation |= DND.DROP_LINK;
	}
	if ((osOperation & COM.DROPEFFECT_MOVE) != 0) {
		operation |= DND.DROP_MOVE;
	}
	return operation;
}

private static int QueryGetData(Transfer[] transferAgents, long pFormatetc) {
	if (transferAgents == null) return COM.E_FAIL;
	TransferData transferData = new TransferData();
	transferData.formatetc = new FORMATETC();
	COM.MoveMemory(transferData.formatetc, pFormatetc, FORMATETC.sizeof);
	transferData.type = transferData.formatetc.cfFormat;

	// is this type supported by the transfer agent?
	for (Transfer transferAgent : transferAgents) {
		if (transferAgent != null && transferAgent.isSupportedType(transferData))
			return COM.S_OK;
	}

	return COM.DV_E_FORMATETC;
}

/* QueryInterface([in] riid, [out] ppvObject)
 * Ownership of ppvObject transfers from callee to caller so reference count on ppvObject
 * must be incremented before returning.  Caller is responsible for releasing ppvObject.
 */
private static int QueryInterface(COMObject comObject, long riid, long ppvObject) {
	if (riid == 0 || ppvObject == 0)
		return COM.E_INVALIDARG;
	GUID guid = new GUID();
	COM.MoveMemory(guid, riid, GUID.sizeof);

	if (comObject != null && COM.IsEqualGUID(guid, COM.IIDIUnknown)
			|| (COM.IsEqualGUID(guid, COM.IIDIDropSource) && (comObject instanceof COMIDropSource))
			|| (COM.IsEqualGUID(guid, COM.IIDIDataObject) && (comObject instanceof COMIDataObject))) {
		OS.MoveMemory(ppvObject, new long[] {comObject.getAddress()}, C.PTR_SIZEOF);
		comObject.method1(null); // AddRef
		return COM.S_OK;
	}

	OS.MoveMemory(ppvObject, new long[] {0}, C.PTR_SIZEOF);
	return COM.E_NOINTERFACE;
}

/**
 * Removes the listener from the collection of listeners who will
 * be notified when a drag and drop operation is in progress.
 *
 * @param listener the listener which should no longer be notified
 *
 * @exception IllegalArgumentException <ul>
 *    <li>ERROR_NULL_ARGUMENT - if the listener is null</li>
 * </ul>
 * @exception SWTException <ul>
 *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
 * </ul>
 *
 * @see DragSourceListener
 * @see #addDragListener
 * @see #getDragListeners
 */
public void removeDragListener(DragSourceListener listener) {
	if (listener == null) DND.error(SWT.ERROR_NULL_ARGUMENT);
	removeListener(DND.DragStart, listener);
	removeListener(DND.DragSetData, listener);
	removeListener(DND.DragEnd, listener);
}

/**
 * Specifies the drag effect for this DragSource.  This drag effect will be
 * used during a drag and drop operation.
 *
 * @param effect the drag effect that is registered for this DragSource
 *
 * @since 3.3
 */
public void setDragSourceEffect(DragSourceEffect effect) {
	dragEffect = effect;
}

/**
 * Specifies the list of data types that can be transferred by this DragSource.
 * The application must be able to provide data to match each of these types when
 * a successful drop has occurred.
 *
 * @param transferAgents a list of Transfer objects which define the types of data that can be
 * dragged from this source
 */
public void setTransfer(Transfer... transferAgents){
	this.transferAgents = transferAgents;
}

}