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

/*******************************************************************************
 * Copyright (c) 2000, 2006 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.swt.dnd;

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

/**
 *
 * <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>
 * 
 * <code><pre>
 *	// 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("");
 *		}
 *	});
 * </pre></code>
 *
 *
 * <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>
 */
public class DragSource extends Widget {

	// info for registering as a drag source
	Control control;
	Listener controlListener;
	Transfer[] transferAgents = new Transfer[0];
	DragAndDropEffect effect;
	Composite topControl;
	
	// ole interfaces
	COMObject iDropSource;
	COMObject iDataObject;
	int refCount;
	
	//workaround - track the operation performed by the drop target for DragEnd event
	int dataEffect = DND.DROP_NONE;	
	
	static final String DRAGSOURCEID = "DragSource"; //$NON-NLS-1$
	static final int CFSTR_PERFORMEDDROPEFFECT  = Transfer.registerType("Performed DropEffect");	 //$NON-NLS-1$

/**
 * 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 compatability.</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(DRAGSOURCEID) != null) {
		DND.error(DND.ERROR_CANNOT_INIT_DRAG);
	}
	control.setData(DRAGSOURCEID, this);
	createCOMInterfaces();
	this.AddRef();

	controlListener = new Listener() {
		public void handleEvent(Event 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, new Listener() {
		public void handleEvent(Event e) {
			DragSource.this.onDispose();
		}
	});
	if (control instanceof Tree) {
		effect = new TreeDragAndDropEffect((Tree)control);
	} else if (control instanceof Table) {
		effect = new TableDragAndDropEffect((Table)control);
	} else {
		effect = new NoDragAndDropEffect(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.
 * 
 * <p><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></p>
 *
 * @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 #removeDragListener
 * @see DragSourceEvent
 */
public void addDragListener(DragSourceListener listener) {
	if (listener == null) DND.error(SWT.ERROR_NULL_ARGUMENT);
	DNDListener typedListener = new DNDListener(listener);
	addListener(DND.DragStart, typedListener);
	addListener(DND.DragSetData, typedListener);
	addListener(DND.DragEnd, typedListener);
}

private int AddRef() {
	refCount++;
	return refCount;
}

private void createCOMInterfaces() {
	// register each of the interfaces that this object implements
	iDropSource = new COMObject(new int[]{2, 0, 0, 2, 1}){
		public int method0(int[] args) {return QueryInterface(args[0], args[1]);}
		public int method1(int[] args) {return AddRef();}
		public int method2(int[] args) {return Release();}
		public int method3(int[] args) {return QueryContinueDrag(args[0], args[1]);}
		public int method4(int[] args) {return GiveFeedback(args[0]);}
	};
	
	iDataObject = new COMObject(new int[]{2, 0, 0, 2, 2, 1, 2, 3, 2, 4, 1, 1}){
		public int method0(int[] args) {return QueryInterface(args[0], args[1]);}
		public int method1(int[] args) {return AddRef();}
		public int method2(int[] args) {return Release();}
		public int method3(int[] args) {return GetData(args[0], args[1]);}
		// method4 GetDataHere - not implemented
		public int method5(int[] args) {return QueryGetData(args[0]);}
		// method6 GetCanonicalFormatEtc - not implemented
		public int method7(int[] args) {return SetData(args[0], args[1], args[2]);}
		public int method8(int[] args) {return EnumFormatEtc(args[0], args[1]);}
		// method9 DAdvise - not implemented
		// method10 DUnadvise - not implemented
		// method11 EnumDAdvise - not implemented
	};
}

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

private void disposeCOMInterfaces() {
	if (iDropSource != null)
		iDropSource.dispose();
	iDropSource = null;

	if (iDataObject != null)
		iDataObject.dispose();
	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, new Boolean(true));
	ImageData imageData = effect.getDragSourceImage(dragEvent.x, dragEvent.y);
	Image image = null;
	int imagelist = 0;
	if (imageData != null) {
		image = new Image(display, imageData);
		imagelist = createImageList(image);
		if (imagelist != 0) {
			topControl = control.getShell();
			OS.ImageList_BeginDrag(imagelist, 0, 0, 0);
			Point location = topControl.getLocation();
			OS.ImageList_DragEnter(topControl.handle, dragEvent.x - location.x, dragEvent.y - location.y);
		}
	}
	int result = COM.DoDragDrop(iDataObject.getAddress(), iDropSource.getAddress(), operations, pdwEffect);
	if (imagelist != 0) {
		OS.ImageList_DragLeave(topControl.handle);
		OS.ImageList_EndDrag();
		OS.ImageList_Destroy(imagelist);
		imagelist = 0;
		topControl = null;
	}
	if (image != null) {
		image.dispose();
	}
	display.setData(key, oldValue);
	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;
}
int createImageList(Image image) {
	int flags = OS.ILC_MASK;
	if (OS.COMCTL32_MAJOR >= 6 && OS.IsAppThemed ()) {
		flags |= OS.ILC_COLOR32;
	} else {
		int hDC = OS.GetDC (0);
		int bits = OS.GetDeviceCaps (hDC, OS.BITSPIXEL);
		int planes = OS.GetDeviceCaps (hDC, OS.PLANES);
		OS.ReleaseDC (0, hDC);
		int depth = bits * planes;
		switch (depth) {
			case 4: flags |= OS.ILC_COLOR4; break;
			case 8: flags |= OS.ILC_COLOR8; break;
			case 16: flags |= OS.ILC_COLOR16; break;
			case 24: flags |= OS.ILC_COLOR24; break;
			case 32: flags |= OS.ILC_COLOR32; break;
			default: flags |= OS.ILC_COLOR; break;
		}
	}
	if ((control.getStyle() & SWT.RIGHT_TO_LEFT) != 0) flags |= OS.ILC_MIRROR;
	Rectangle bounds = image.getBounds();
	int cx = bounds.width, cy = bounds.height;
	int imageList = OS.ImageList_Create(cx, cy, flags, 0, 1);
	int hImage = image.handle;
	switch (image.type) {
		case SWT.BITMAP: {
			int background = control.getBackground().handle;
			OS.ImageList_AddMasked(imageList, hImage, background);
			break;
		}
		case SWT.ICON: {
			int hDC = OS.GetDC(0);
			int bitmap = OS.CreateCompatibleBitmap(hDC, cx, cy);
			int hDC1 = OS.CreateCompatibleDC(hDC);
			int hOldBitmap = OS.SelectObject(hDC1, bitmap);
			int hIcon = OS.CopyImage(image.handle, OS.IMAGE_ICON, cx, cy, 0);
			OS.DrawIconEx(hDC1, 0, 0, hIcon, 0, 0, 0, 0, OS.DI_NORMAL);
			OS.DestroyIcon(hIcon);
			OS.SelectObject(hDC1, hOldBitmap);
			ImageData imageData = image.getImageData();
			int background = imageData.transparentPixel;
			OS.ImageList_AddMasked(imageList, bitmap, background);
			OS.DeleteObject(bitmap);
			OS.DeleteDC (hDC1);
			OS.ReleaseDC (0, hDC);
			break;
		}
		default: {
			OS.ImageList_Destroy(imageList);
			imageList = 0;
		}
	}
	return imageList;
}
/* 
 * 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 int EnumFormatEtc(int dwDirection, int 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 (int i = 0; i < transferAgents.length; i++){
		TransferData[] formats = transferAgents[i].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 int[] {enumFORMATETC.getAddress()}, 4);
	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;
}

private int GetData(int pFormatetc, int 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(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;
	
	DNDEvent event = new DNDEvent();
	event.widget = this;
	event.time = OS.GetMessageTime();
	event.dataType = transferData;
	notifyListeners(DND.DragSetData,event);
	
	// get matching transfer agent to perform conversion
	Transfer transfer = null;
	for (int i = 0; i < transferAgents.length; i++){
		if (transferAgents[i].isSupportedType(transferData)){
			transfer = transferAgents[i];
			break;
		}
	}
	
	if (transfer == null) return COM.DV_E_FORMATETC;
	transfer.javaToNative(event.data, transferData);
	if (transferData.result != COM.S_OK) return transferData.result;
	COM.MoveMemory(pmedium, transferData.stgmedium, STGMEDIUM.sizeof);
	return transferData.result;
}

/**
 * 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 (fEscapePressed != 0){
		if (topControl != null) OS.ImageList_DragLeave(topControl.handle);
		return COM.DRAGDROP_S_CANCEL;
	}
	int mask = OS.MK_LBUTTON | OS.MK_MBUTTON | OS.MK_RBUTTON | OS.MK_XBUTTON1 | OS.MK_XBUTTON2;
	if ((grfKeyState & mask) == 0) {
		if (topControl != null) OS.ImageList_DragLeave(topControl.handle);
		return COM.DRAGDROP_S_DROP;
	}
	
	if (topControl != null) {
		Display display = getDisplay();
		Point pt = display.getCursorLocation();
		Point location = topControl.getLocation();
		OS.ImageList_DragMove(pt.x - location.x, pt.y - location.y);
	}
	return COM.S_OK;
}

private void onDispose() {
	if (control == null) return;
	this.Release();
	if (controlListener != null){
		control.removeListener(SWT.Dispose, controlListener);
		control.removeListener(SWT.DragDetect, controlListener);
	}
	controlListener = null;
	control.setData(DRAGSOURCEID, 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 int QueryGetData(int 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 (int i = 0; i < transferAgents.length; i++){
		if (transferAgents[i].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 int QueryInterface(int riid, int ppvObject) {
	if (riid == 0 || ppvObject == 0)
		return COM.E_INVALIDARG;
	GUID guid = new GUID();
	COM.MoveMemory(guid, riid, GUID.sizeof);
	
	if (COM.IsEqualGUID(guid, COM.IIDIUnknown) || COM.IsEqualGUID(guid, COM.IIDIDropSource)) {
		OS.MoveMemory(ppvObject, new int[] {iDropSource.getAddress()}, 4);
		AddRef();
		return COM.S_OK;
	}

	if (COM.IsEqualGUID(guid, COM.IIDIDataObject) ) {
		OS.MoveMemory(ppvObject, new int[] {iDataObject.getAddress()}, 4);
		AddRef();
		return COM.S_OK;
	}
	
	OS.MoveMemory(ppvObject, new int[] {0}, 4);
	return COM.E_NOINTERFACE;
}

private int Release() {
	refCount--;
	if (refCount == 0) {
		disposeCOMInterfaces();
		COM.CoFreeUnusedLibraries();
	}
	return refCount;
}

/**
 * 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 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
 */
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);
}

private int SetData(int pFormatetc, int 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);
		int[] ptrEffect = new int[1];
		OS.MoveMemory(ptrEffect, stgmedium.unionField,4);
		int[] effect = new int[1];
		OS.MoveMemory(effect, ptrEffect[0],4);
		dataEffect = osToOp(effect[0]);
	}
	if (fRelease == 1) {
		COM.ReleaseStgMedium(pmedium);
	}
	return COM.S_OK;
}

/**
 * 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;
}

}