Class DragSource
DragSource
defines the source object for a drag and drop transfer.
IMPORTANT: This class is not intended to be subclassed.
A drag source is the object which originates a drag and drop operation. For the specified widget,
it defines the type of data that is available for dragging and the set of operations that can
be performed on that data. The operations can be any bit-wise combination of DND.MOVE, DND.COPY or
DND.LINK. The type of data that can be transferred is specified by subclasses of Transfer such as
TextTransfer or FileTransfer. The type of data transferred can be a predefined system type or it
can be a type defined by the application. For instructions on how to define your own transfer type,
refer to ByteArrayTransfer
.
You may have several DragSources in an application but you can only have one DragSource per Control. Data dragged from this DragSource can be dropped on a site within this application or it can be dropped on another application such as an external Text editor.
The application supplies the content of the data being transferred by implementing the
DragSourceListener
and associating it with the DragSource via DragSource#addDragListener.
When a successful move operation occurs, the application is required to take the appropriate action to remove the data from its display and remove any associated operating system resources or internal references. Typically in a move operation, the drop target makes a copy of the data and the drag source deletes the original. However, sometimes copying the data can take a long time (such as copying a large file). Therefore, on some platforms, the drop target may actually move the data in the operating system rather than make a copy. This is usually only done in file transfers. In this case, the drag source is informed in the DragEnd event that a DROP_TARGET_MOVE was performed. It is the responsibility of the drag source at this point to clean up its displayed information. No action needs to be taken on the operating system resources.
The following example shows a Label widget that allows text to be dragged from it.
// Enable a label as a Drag Source
Label label = new Label(shell, SWT.NONE);
// This example will allow text to be dragged
Transfer[] types = new Transfer[] {TextTransfer.getInstance()};
// This example will allow the text to be copied or moved to the drop target
int operations = DND.DROP_MOVE | DND.DROP_COPY;
DragSource source = new DragSource(label, operations);
source.setTransfer(types);
source.addDragListener(new DragSourceListener() {
public void dragStart(DragSourceEvent e) {
// Only start the drag if there is actually text in the
// label - this text will be what is dropped on the target.
if (label.getText().length() == 0) {
event.doit = false;
}
};
public void dragSetData(DragSourceEvent event) {
// A drop has been performed, so provide the data of the
// requested type.
// (Checking the type of the requested data is only
// necessary if the drag source supports more than
// one data type but is shown here as an example).
if (TextTransfer.getInstance().isSupportedType(event.dataType)){
event.data = label.getText();
}
}
public void dragFinished(DragSourceEvent event) {
// A Move operation has been performed so remove the data
// from the source
if (event.detail == DND.DROP_MOVE)
label.setText("");
}
});
- Styles
- DND.DROP_NONE, DND.DROP_COPY, DND.DROP_MOVE, DND.DROP_LINK
- Events
- DND.DragStart, DND.DragSetData, DND.DragEnd
- See Also:
- Restriction:
- This class is not intended to be subclassed by clients.
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Field Summary
Fields inherited from class org.eclipse.swt.widgets.Widget
nativeZoom
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Constructor Summary
ConstructorDescriptionDragSource
(Control control, int style) Creates a newDragSource
to handle dragging from the specifiedControl
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Method Summary
Modifier and TypeMethodDescriptionvoid
addDragListener
(DragSourceListener 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 theDragSourceListener
interface.protected void
Checks that this class can be subclassed.Returns the Control which is registered for this DragSource.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 theDragSourceListener
interface.Returns the drag effect that is registered for this DragSource.Transfer[]
Returns the list of data types that can be transferred by this DragSource.void
removeDragListener
(DragSourceListener listener) Removes the listener from the collection of listeners who will be notified when a drag and drop operation is in progress.void
setDragSourceEffect
(DragSourceEffect effect) Specifies the drag effect for this DragSource.void
setTransfer
(Transfer... transferAgents) Specifies the list of data types that can be transferred by this DragSource.Methods inherited from class org.eclipse.swt.widgets.Widget
addDisposeListener, addListener, addTypedListener, checkWidget, dispose, getData, getData, getDisplay, getListeners, getStyle, getTypedListeners, isAutoDirection, isDisposed, isListening, notifyListeners, removeDisposeListener, removeListener, removeListener, removeTypedListener, reskin, setData, setData, toString
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Constructor Details
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DragSource
Creates a newDragSource
to handle dragging from the specifiedControl
. Creating an instance of a DragSource may cause system resources to be allocated depending on the platform. It is therefore mandatory that the DragSource instance be disposed when no longer required.- Parameters:
control
- theControl
that the user clicks on to initiate the dragstyle
- 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_DRAG - unable to initiate drag source; this will occur if more than one drag source is created for a control or if the operating system will not allow the creation of the drag source
NOTE: ERROR_CANNOT_INIT_DRAG should be an SWTException, since it is a recoverable error, but can not be changed due to backward compatibility.
- See Also:
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Method Details
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addDragListener
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 theDragSourceListener
interface.dragStart
is called when the user has begun the actions required to drag the widget. This event gives the application the chance to decide if a drag should be started.dragSetData
is called when the data is required from the drag source.dragFinished
is called when the drop has successfully completed (mouse up over a valid target) or has been terminated (such as hitting the ESC key). Perform cleanup such as removing data from the source side on a successful move operation.
- 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:
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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
Returns the Control which is registered for this DragSource. This is the control that the user clicks in to initiate dragging.- Returns:
- the Control which is registered for this DragSource
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getDragListeners
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 theDragSourceListener
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:
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getDragSourceEffect
Returns the drag effect that is registered for this DragSource. This drag effect will be used during a drag and drop operation.- Returns:
- the drag effect that is registered for this DragSource
- Since:
- 3.3
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getTransfer
Returns the list of data types that can be transferred by this DragSource.- Returns:
- the list of data types that can be transferred by this DragSource
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removeDragListener
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:
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setDragSourceEffect
Specifies the drag effect for this DragSource. This drag effect will be used during a drag and drop operation.- Parameters:
effect
- the drag effect that is registered for this DragSource- Since:
- 3.3
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setTransfer
Specifies the list of data types that can be transferred by this DragSource. The application must be able to provide data to match each of these types when a successful drop has occurred.- Parameters:
transferAgents
- a list of Transfer objects which define the types of data that can be dragged from this source
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