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org.eclipse.swt.dnd
Class DropTarget
java.lang.Object
org.eclipse.swt.widgets.Widget
org.eclipse.swt.dnd.DropTarget
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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
}
});
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Styles
- DND.DROP_NONE, DND.DROP_COPY, DND.DROP_MOVE, DND.DROP_LINK
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Events
- DND.DragEnter, DND.DragLeave, DND.DragOver, DND.DragOperationChanged,
DND.DropAccept, DND.Drop
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See Also:
-
Drag and Drop snippets,
SWT Example: DNDExample,
Sample code and further information
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Restriction:
- This class is not intended to be subclassed by clients.
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Constructor Summary
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DropTarget
(
Control control,
int style)
Creates a new DropTarget to allow data to be dropped on the specified
Control. |
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Method Summary
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void
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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
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checkSubclass
()
Checks that this class can be subclassed. |
Control
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getControl
()
Returns the Control which is registered for this DropTarget. |
DropTargetListener[]
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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
the DropTargetListener interface. |
DropTargetEffect
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getDropTargetEffect
()
Returns the drop effect for this DropTarget. |
Transfer[]
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getTransfer
()
Returns a list of the data types that can be transferred to this DropTarget. |
void
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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
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setDropTargetEffect
(
DropTargetEffect effect)
Specifies the drop effect for this DropTarget. |
void
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setTransfer
(
Transfer[] transferAgents)
Specifies the data types that can be transferred to this DropTarget. |
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Methods inherited from class org.eclipse.swt.widgets.
Widget
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addDisposeListener,
addListener,
checkWidget,
dispose,
getData,
getData,
getDisplay,
getListeners,
getStyle,
isDisposed,
isListening,
notifyListeners,
removeDisposeListener,
removeListener,
removeListener,
setData,
setData,
toString
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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.
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Parameters:
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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
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Throws:
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SWTException
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- 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
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SWTError
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- 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.
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See Also:
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Widget.dispose(),
checkSubclass(),
DND.DROP_NONE,
DND.DROP_COPY,
DND.DROP_MOVE,
DND.DROP_LINK
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.
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dragEnter is called when the cursor has entered the drop target boundaries
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dragLeave is called when the cursor has left the drop target boundaries and just before
the drop occurs or is cancelled.
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dragOperationChanged is called when the operation being performed has changed
(usually due to the user changing the selected modifier key(s) while dragging)
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dragOver is called when the cursor is moving over the drop target
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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
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drop is called when the data is being dropped
-
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Parameters:
-
listener - the listener which should be notified
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Throws:
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IllegalArgumentException
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- ERROR_NULL_ARGUMENT - if the listener is null
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SWTException
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- ERROR_WIDGET_DISPOSED - if the receiver has been disposed
- ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver
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See Also:
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DropTargetListener,
getDropListeners(),
removeDropListener(org.eclipse.swt.dnd.DropTargetListener),
DropTargetEvent
checkSubclass
protected void checkSubclass()
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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.
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Overrides:
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checkSubclass
in class
Widget
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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
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
the
DropTargetListener interface.
-
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Returns:
- the listeners who will be notified when a drag and drop
operation is in progress
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Throws:
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SWTException
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- ERROR_WIDGET_DISPOSED - if the receiver has been disposed
- ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver
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Since:
- 3.4
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See Also:
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DropTargetListener,
addDropListener(org.eclipse.swt.dnd.DropTargetListener),
removeDropListener(org.eclipse.swt.dnd.DropTargetListener),
DropTargetEvent
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.
-
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Returns:
- the drop effect that is registered for this DropTarget
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Since:
- 3.3
getTransfer
public
Transfer[] getTransfer()
- Returns a list of the data types that can be transferred to this DropTarget.
-
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Returns:
- a list of the data types that can be transferred to this DropTarget
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.
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Parameters:
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listener - the listener which should no longer be notified
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Throws:
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IllegalArgumentException
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- ERROR_NULL_ARGUMENT - if the listener is null
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SWTException
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- ERROR_WIDGET_DISPOSED - if the receiver has been disposed
- ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver
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See Also:
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DropTargetListener,
addDropListener(org.eclipse.swt.dnd.DropTargetListener),
getDropListeners()
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.
-
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Parameters:
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effect - the drop effect that is registered for this DropTarget -
Since:
- 3.3
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.
-
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Parameters:
-
transferAgents - a list of Transfer objects which define the types of data that can be
dropped on this target
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Throws:
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IllegalArgumentException
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- ERROR_NULL_ARGUMENT - if transferAgents is null
Guidelines for using Eclipse APIs.
Copyright (c) Eclipse contributors and others 2000, 2008. All rights reserved.
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