Class DropTarget
- java.lang.Object
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- org.eclipse.swt.widgets.Widget
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- org.eclipse.swt.dnd.DropTarget
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public class DropTarget extends Widget
ClassDropTarget
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 aControl
and aDropTarget
. 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 classDropTargetEvent
. The application can modify the type of drag being performed on this Control at any stage of the drag by modifying theevent.detail
field or theevent.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
- See Also:
- Drag and Drop snippets, SWT Example: DNDExample, Sample code and further information
- Restriction:
- This class is not intended to be subclassed by clients.
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Constructor Summary
Constructors Constructor Description DropTarget(Control control, int style)
Creates a newDropTarget
to allow data to be dropped on the specifiedControl
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description 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 theDropTargetListener
interface.protected void
checkSubclass()
Checks that this class can be subclassed.Control
getControl()
Returns the Control which is registered for this DropTarget.DropTargetListener[]
getDropListeners()
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 theDropTargetListener
interface.DropTargetEffect
getDropTargetEffect()
Returns the drop effect for this DropTarget.Transfer[]
getTransfer()
Returns a list of the data types that can be transferred to this DropTarget.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
setDropTargetEffect(DropTargetEffect effect)
Specifies the drop effect for this DropTarget.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, getListeners, getStyle, isAutoDirection, isDisposed, isListening, notifyListeners, removeDisposeListener, removeListener, removeListener, reskin, setData, setData, toString
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Constructor Detail
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DropTarget
public DropTarget(Control control, int style)
Creates a newDropTarget
to allow data to be dropped on the specifiedControl
. 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
- theControl
over which the user positions the cursor to drop the datastyle
- 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
NOTE: ERROR_CANNOT_INIT_DROP should be an SWTException, since it is a recoverable error, but can not be changed due to backward compatibility.
- See Also:
Widget.dispose()
,checkSubclass()
,DND.DROP_NONE
,DND.DROP_COPY
,DND.DROP_MOVE
,DND.DROP_LINK
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Method Detail
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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 theDropTargetListener
interface.dragEnter
is called when the cursor has entered the drop target boundariesdragLeave
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 targetdropAccept
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 theevent.detail
fielddrop
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
,getDropListeners()
,removeDropListener(org.eclipse.swt.dnd.DropTargetListener)
,DropTargetEvent
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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
andCanvas
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 classWidget
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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
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getDropListeners
public DropTargetListener[] getDropListeners()
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 theDropTargetListener
interface.- Returns:
- the listeners who will be notified when a drag and drop operation is in progress
- Throws:
SWTException
-- ERROR_WIDGET_DISPOSED - if the receiver has been disposed
- ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver
- Since:
- 3.4
- See Also:
DropTargetListener
,addDropListener(org.eclipse.swt.dnd.DropTargetListener)
,removeDropListener(org.eclipse.swt.dnd.DropTargetListener)
,DropTargetEvent
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getDropTargetEffect
public DropTargetEffect getDropTargetEffect()
Returns the drop effect for this DropTarget. This drop effect will be used during a drag and drop to display the drag under effect on the target widget.- Returns:
- the drop effect that is registered for this DropTarget
- Since:
- 3.3
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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
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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 no longer 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)
,getDropListeners()
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setDropTargetEffect
public void setDropTargetEffect(DropTargetEffect effect)
Specifies the drop effect for this DropTarget. This drop effect will be used during a drag and drop to display the drag under effect on the target widget.- Parameters:
effect
- the drop effect that is registered for this DropTarget- Since:
- 3.3
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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
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