org.eclipse.swt.dnd
Class DropTarget

java.lang.Object
  |
  +--org.eclipse.swt.widgets.Widget
        |
        +--org.eclipse.swt.dnd.DropTarget

public class DropTarget

extends Widget

Untamed: Class DropTarget defines the target object for a drag and drop transfer. IMPORTANT: This class is not intended to be subclassed.

This class identifies the Control 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 Control and a DropTarget. The DropTarget can receive data from within the same application or from other applications (such as text dragged from a text editor like Word).

	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);
 

The application is notified of data being dragged over this control and of when a drop occurs by implementing the interface DropTargetListener which uses the class DropTargetEvent. The application can modify the type of drag being performed on this Control at any stage of the drag by modifying the event.detail field or the event.currentDataType field. When the data is dropped, it is the responsibility of the application to copy this data for its own purposes.

	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
		}
 	});
 

Styles

DND.DROP_NONE, DND.DROP_COPY, DND.DROP_MOVE, DND.DROP_LINK

Events

DND.DragEnter, DND.DragLeave, DND.DragOver, DND.DragOperationChanged, DND.DropAccept, DND.Drop

Field Summary

private Control	control
private Listener	controlListener
private TransferData[]	dataTypes
private static String	DROPTARGETID
private DragUnderEffect	effect
private int	iDataObject
private org.eclipse.swt.internal.ole.win32.COMObject	iDropTarget
private int	keyState
private int	lastOperation
private int	refCount
private TransferData	selectedDataType
private Transfer[]	transferAgents

Fields inherited from class org.eclipse.swt.widgets.Widget

Constructor Summary

DropTarget(Control control, int style)
Enabled: Creates a new DropTarget to allow data to be dropped on the specified Control.

Method Summary

void	addDropListener(DropTargetListener listener) Enabled: 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 DropTargetListener interface.
private int	AddRef()
(package private) static int	checkStyle(int style)
protected void	checkSubclass() Checks that this class can be subclassed.
private void	createCOMInterfaces()
private void	disposeCOMInterfaces()
private int	DragEnter(int pDataObject, int grfKeyState, int pt_x, int pt_y, int pdwEffect)
private int	DragLeave()
private int	DragOver(int grfKeyState, int pt_x, int pt_y, int pdwEffect)
private int	Drop(int pDataObject, int grfKeyState, int pt_x, int pt_y, int pdwEffect)
Control	getControl() Enabled: Returns the Control which is registered for this DropTarget.
Display	getDisplay() Enabled:
private int	getOperationFromKeyState(int grfKeyState)
Transfer[]	getTransfer() Enabled: Returns a list of the data types that can be transferred to this DropTarget.
void	notifyListeners(int eventType, Event event) Enabled:
private void	onDispose()
private int	opToOs(int operation)
private int	osToOp(int osOperation)
private int	QueryInterface(int riid, int ppvObject)
private int	Release()
void	removeDropListener(DropTargetListener listener) Enabled: Removes the listener from the collection of listeners who will be notified when a drag and drop operation is in progress.
void	setTransfer(Transfer[] transferAgents) Enabled: Specifies the data types that can be transferred to this DropTarget.

Methods inherited from class org.eclipse.swt.widgets.Widget

addDisposeListener, addListener, checkWidget, dispose, getData, getData, getStyle, isDisposed, isListening, removeDisposeListener, removeListener, removeListener, setData, setData, toString

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

control

private Control control

controlListener

private Listener controlListener

transferAgents

private Transfer[] transferAgents

effect

private DragUnderEffect effect

DROPTARGETID

private static final String DROPTARGETID

iDropTarget

private org.eclipse.swt.internal.ole.win32.COMObject iDropTarget

refCount

private int refCount

selectedDataType

private TransferData selectedDataType

dataTypes

private TransferData[] dataTypes

lastOperation

private int lastOperation

keyState

private int keyState

iDataObject

private int iDataObject

Constructor Detail

DropTarget

public DropTarget(Control control,
                  int style)

Enabled: Creates a new DropTarget to allow data to be dropped on the specified Control. Creating an instance of a DropTarget may cause system resources to be allocated depending on the platform. It is therefore mandatory that the DropTarget instance be disposed when no longer required.

Parameters:

control - the Control over which the user positions the cursor to drop the data

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 Also:

Widget.dispose(), checkSubclass(), DND.DROP_NONE, DND.DROP_COPY, DND.DROP_MOVE, DND.DROP_LINK

Method Detail

addDropListener

public void addDropListener(DropTargetListener listener)

Enabled: 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 DropTargetListener interface.

• dragEnter is called when the cursor has entered the drop target boundaries
• dragLeave is called when the cursor has left the drop target boundaries and just before the drop occurs or is cancelled.
• dragOperationChanged is called when the operation being performed has changed (usually due to the user changing the selected modifier key(s) while dragging)
• dragOver is called when the cursor is moving over the drop target
• dropAccept is called just before the drop is performed. The drop target is given the chance to change the nature of the drop or veto the drop by setting the event.detail field
• drop is called when the data is being dropped

Parameters:

listener - the listener which should be notified

See Also:

DropTargetListener, removeDropListener(org.eclipse.swt.dnd.DropTargetListener), DropTargetEvent

AddRef

private int AddRef()

checkStyle

static int checkStyle(int style)

checkSubclass

protected void checkSubclass()

Description copied from class: Widget

Checks that this class can be subclassed.

The SWT class library is intended to be subclassed only at specific, controlled points (most notably, Composite and Canvas when implementing new widgets). This method enforces this rule unless it is overridden.

IMPORTANT: By providing an implementation of this method that allows a subclass of a class which does not normally allow subclassing to be created, the implementer agrees to be fully responsible for the fact that any such subclass will likely fail between SWT releases and will be strongly platform specific. No support is provided for user-written classes which are implemented in this fashion.

The ability to subclass outside of the allowed SWT classes is intended purely to enable those not on the SWT development team to implement patches in order to get around specific limitations in advance of when those limitations can be addressed by the team. Subclassing should not be attempted without an intimate and detailed understanding of the hierarchy.

Overrides:

checkSubclass in class Widget

createCOMInterfaces

private void createCOMInterfaces()

disposeCOMInterfaces

private void disposeCOMInterfaces()

DragEnter

private int DragEnter(int pDataObject,
                      int grfKeyState,
                      int pt_x,
                      int pt_y,
                      int pdwEffect)

DragLeave

private int DragLeave()

DragOver

private int DragOver(int grfKeyState,
                     int pt_x,
                     int pt_y,
                     int pdwEffect)

Drop

private int Drop(int pDataObject,
                 int grfKeyState,
                 int pt_x,
                 int pt_y,
                 int pdwEffect)

getControl

public Control getControl()

Enabled: Returns the Control which is registered for this DropTarget. This is the control over which the user positions the cursor to drop the data.

Returns:

the Control which is registered for this DropTarget

getDisplay

public Display getDisplay()

Enabled:

Specified by:

getDisplay in class Widget

Returns:

the receiver's display

getOperationFromKeyState

private int getOperationFromKeyState(int grfKeyState)

getTransfer

public Transfer[] getTransfer()

Enabled: Returns a list of the data types that can be transferred to this DropTarget.

Returns:

a list of the data types that can be transferred to this DropTarget

notifyListeners

public void notifyListeners(int eventType,
                            Event event)

Enabled:

Overrides:

notifyListeners in class Widget

Parameters:

eventType - the type of event which has occurred

event - the event data

onDispose

private void onDispose()

opToOs

private int opToOs(int operation)

osToOp

private int osToOp(int osOperation)

QueryInterface

private int QueryInterface(int riid,
                           int ppvObject)

Release

private int Release()

removeDropListener

public void removeDropListener(DropTargetListener listener)

Enabled: Removes the listener from the collection of listeners who will be notified when a drag and drop operation is in progress.

Parameters:

listener - the listener which should be notified

See Also:

DropTargetListener, addDropListener(org.eclipse.swt.dnd.DropTargetListener)

setTransfer

public void setTransfer(Transfer[] transferAgents)

Enabled: Specifies the data types that can be transferred to this DropTarget. If data is being dragged that does not match one of these types, the drop target will be notified of the drag and drop operation but the currentDataType will be null and the operation will be DND.NONE.

Parameters:

transferAgents - a list of Transfer objects which define the types of data that can be dropped on this target