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Eclipse Platform
Release 3.0

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org.eclipse.swt.dnd
Class DropTarget

java.lang.Object
  org.eclipse.swt.widgets.Widget
      org.eclipse.swt.dnd.DropTarget

public class DropTarget

extends Widget

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

Constructor Summary

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

Method Summary

void	addDropListener(DropTargetListener listener) 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.
protected void	checkSubclass() Checks that this class can be subclassed.
Control	getControl() Returns the Control which is registered for this DropTarget.
Transfer[]	getTransfer() Returns a list of the data types that can be transferred to this DropTarget.
void	notifyListeners(int eventType, Event event) Notifies all of the receiver's listeners for events of the given type that one such event has occurred by invoking their handleEvent() method.
void	removeDropListener(DropTargetListener listener) 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) 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, getDisplay, 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

Constructor Detail

DropTarget

public DropTarget(Control control,
                  int style)

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

Throws:

SWTException -

• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the parent
• ERROR_INVALID_SUBCLASS - if this class is not an allowed subclass
  SWTError -

  • ERROR_CANNOT_INIT_DROP - unable to initiate drop target; this will occur if more than one drop target is created for a control or if the operating system will not allow the creation of the drop target

  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)

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

Throws:

IllegalArgumentException -

• ERROR_NULL_ARGUMENT - if the listener is null

SWTException -

• ERROR_WIDGET_DISPOSED - if the receiver has been disposed
• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver

See Also:

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

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

getControl

public Control getControl()

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

getTransfer

public Transfer[] getTransfer()

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)

Description copied from class: Widget

Notifies all of the receiver's listeners for events of the given type that one such event has occurred by invoking their handleEvent() method.

Overrides:

notifyListeners in class Widget

Parameters:

eventType - the type of event which has occurred

event - the event data

removeDropListener

public void removeDropListener(DropTargetListener listener)

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

Throws:

IllegalArgumentException -

• ERROR_NULL_ARGUMENT - if the listener is null

SWTException -

• ERROR_WIDGET_DISPOSED - if the receiver has been disposed
• ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver

See Also:

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

setTransfer

public void setTransfer(Transfer[] transferAgents)

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

Throws:

IllegalArgumentException -

• ERROR_NULL_ARGUMENT - if transferAgents is null