Eclipse Rich Ajax Platform

org.eclipse.swt.dnd
Class DropTarget

java.lang.Object
  extended by org.eclipse.swt.widgets.Widget
      extended by org.eclipse.swt.dnd.DropTarget
All Implemented Interfaces:
Adaptable

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

Since:
1.3

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.
 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.
 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, getAdapter, getData, getData, getDisplay, getListeners, getStyle, isDisposed, isListening, notifyListeners, removeDisposeListener, removeListener, reskin, 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

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
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.

Parameters:
listener - the listener which should be notified
Throws:
java.lang.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

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

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.

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
See Also:
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.

Returns:
the drop effect that 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

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:
java.lang.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()

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

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:
java.lang.IllegalArgumentException -
  • ERROR_NULL_ARGUMENT - if transferAgents is null

Eclipse Rich Ajax Platform

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