public class DragSourceContext extends Object implements DragSourceListener, DragSourceMotionListener, Serializable
DragSourceContext
class is responsible for managing the
initiator side of the Drag and Drop protocol. In particular, it is responsible
for managing drag event notifications to the
DragSourceListeners
and DragSourceMotionListeners, and providing the
Transferable
representing the source data for the drag operation.
Note that the DragSourceContext
itself
implements the DragSourceListener
and
DragSourceMotionListener
interfaces.
This is to allow the platform peer
(the DragSourceContextPeer
instance)
created by the DragSource
to notify
the DragSourceContext
of
state changes in the ongoing operation. This allows the
DragSourceContext
object to interpose
itself between the platform and the
listeners provided by the initiator of the drag operation.
By default, DragSourceContext
sets the cursor as appropriate
for the current state of the drag and drop operation. For example, if
the user has chosen the move action,
and the pointer is over a target that accepts
the move action, the default move cursor is shown. When
the pointer is over an area that does not accept the transfer,
the default "no drop" cursor is shown.
This default handling mechanism is disabled when a custom cursor is set
by the setCursor(java.awt.Cursor)
method. When the default handling is disabled,
it becomes the responsibility
of the developer to keep the cursor up to date, by listening
to the DragSource
events and calling the setCursor()
method.
Alternatively, you can provide custom cursor behavior by providing
custom implementations of the DragSource
and the DragSourceContext
classes.
DragSourceListener
,
DragSourceMotionListener
,
DnDConstants
,
Serialized FormModifier and Type | Field and Description |
---|---|
protected static int |
CHANGED
An
int used by updateCurrentCursor()
indicating that the user operation has changed. |
protected static int |
DEFAULT
An
int used by updateCurrentCursor()
indicating that the Cursor should change
to the default (no drop) Cursor . |
protected static int |
ENTER
An
int used by updateCurrentCursor()
indicating that the Cursor
has entered a DropTarget . |
protected static int |
OVER
An
int used by updateCurrentCursor()
indicating that the Cursor is
over a DropTarget . |
Constructor and Description |
---|
DragSourceContext(java.awt.dnd.peer.DragSourceContextPeer dscp,
DragGestureEvent trigger,
Cursor dragCursor,
Image dragImage,
Point offset,
Transferable t,
DragSourceListener dsl)
Called from
DragSource , this constructor creates a new
DragSourceContext given the
DragSourceContextPeer for this Drag, the
DragGestureEvent that triggered the Drag, the initial
Cursor to use for the Drag, an (optional)
Image to display while the Drag is taking place, the offset
of the Image origin from the hotspot at the instant of the
triggering event, the Transferable subject data, and the
DragSourceListener to use during the Drag and Drop
operation. |
Modifier and Type | Method and Description |
---|---|
void |
addDragSourceListener(DragSourceListener dsl)
Add a
DragSourceListener to this
DragSourceContext if one has not already been added. |
void |
dragDropEnd(DragSourceDropEvent dsde)
Calls
dragDropEnd on the
DragSourceListener s registered with this
DragSourceContext and with the associated
DragSource , and passes them the specified
DragSourceDropEvent . |
void |
dragEnter(DragSourceDragEvent dsde)
Calls
dragEnter on the
DragSourceListener s registered with this
DragSourceContext and with the associated
DragSource , and passes them the specified
DragSourceDragEvent . |
void |
dragExit(DragSourceEvent dse)
Calls
dragExit on the
DragSourceListener s registered with this
DragSourceContext and with the associated
DragSource , and passes them the specified
DragSourceEvent . |
void |
dragMouseMoved(DragSourceDragEvent dsde)
Calls
dragMouseMoved on the
DragSourceMotionListener s registered with the
DragSource associated with this
DragSourceContext , and them passes the specified
DragSourceDragEvent . |
void |
dragOver(DragSourceDragEvent dsde)
Calls
dragOver on the
DragSourceListener s registered with this
DragSourceContext and with the associated
DragSource , and passes them the specified
DragSourceDragEvent . |
void |
dropActionChanged(DragSourceDragEvent dsde)
Calls
dropActionChanged on the
DragSourceListener s registered with this
DragSourceContext and with the associated
DragSource , and passes them the specified
DragSourceDragEvent . |
Component |
getComponent()
Returns the
Component associated with this
DragSourceContext . |
Cursor |
getCursor()
Returns the current drag
Cursor . |
DragSource |
getDragSource()
Returns the
DragSource
that instantiated this DragSourceContext . |
int |
getSourceActions()
Returns a bitwise mask of
DnDConstants that
represent the set of drop actions supported by the drag source for the
drag operation associated with this DragSourceContext . |
Transferable |
getTransferable()
Returns the
Transferable associated with
this DragSourceContext . |
DragGestureEvent |
getTrigger()
Returns the
DragGestureEvent
that initially triggered the drag. |
void |
removeDragSourceListener(DragSourceListener dsl)
Removes the specified
DragSourceListener
from this DragSourceContext . |
void |
setCursor(Cursor c)
Sets the cursor for this drag operation to the specified
Cursor . |
void |
transferablesFlavorsChanged()
Notifies the peer that the
Transferable 's
DataFlavor s have changed. |
protected void |
updateCurrentCursor(int sourceAct,
int targetAct,
int status)
If the default drag cursor behavior is active, this method
sets the default drag cursor for the specified actions
supported by the drag source, the drop target action,
and status, otherwise this method does nothing.
|
protected static final int DEFAULT
int
used by updateCurrentCursor()
indicating that the Cursor
should change
to the default (no drop) Cursor
.protected static final int ENTER
int
used by updateCurrentCursor()
indicating that the Cursor
has entered a DropTarget
.protected static final int OVER
int
used by updateCurrentCursor()
indicating that the Cursor
is
over a DropTarget
.protected static final int CHANGED
int
used by updateCurrentCursor()
indicating that the user operation has changed.public DragSourceContext(java.awt.dnd.peer.DragSourceContextPeer dscp, DragGestureEvent trigger, Cursor dragCursor, Image dragImage, Point offset, Transferable t, DragSourceListener dsl)
DragSource
, this constructor creates a new
DragSourceContext
given the
DragSourceContextPeer
for this Drag, the
DragGestureEvent
that triggered the Drag, the initial
Cursor
to use for the Drag, an (optional)
Image
to display while the Drag is taking place, the offset
of the Image
origin from the hotspot at the instant of the
triggering event, the Transferable
subject data, and the
DragSourceListener
to use during the Drag and Drop
operation.
DragSourceContextPeer
is null
NullPointerException
is thrown.
DragGestureEvent
is null
NullPointerException
is thrown.
Cursor
is null
no exception is thrown and
the default drag cursor behavior is activated for this drag operation.
Image
is null
no exception is thrown.
Image
is not null
and the offset is
null
NullPointerException
is thrown.
Transferable
is null
NullPointerException
is thrown.
DragSourceListener
is null
no exception
is thrown.dscp
- the DragSourceContextPeer
for this dragtrigger
- the triggering eventdragCursor
- the initial Cursor
for this drag operation
or null
for the default cursor handling;
see class level documentation
for more details on the cursor handling mechanism during drag and dropdragImage
- the Image
to drag (or null
)offset
- the offset of the image origin from the hotspot at the
instant of the triggering eventt
- the Transferable
dsl
- the DragSourceListener
IllegalArgumentException
- if the Component
associated
with the trigger event is null
.IllegalArgumentException
- if the DragSource
for the
trigger event is null
.IllegalArgumentException
- if the drag action for the
trigger event is DnDConstants.ACTION_NONE
.IllegalArgumentException
- if the source actions for the
DragGestureRecognizer
associated with the trigger
event are equal to DnDConstants.ACTION_NONE
.NullPointerException
- if dscp, trigger, or t are null, or
if dragImage is non-null and offset is nullpublic DragSource getDragSource()
DragSource
that instantiated this DragSourceContext
.DragSource
that
instantiated this DragSourceContext
public Component getComponent()
Component
associated with this
DragSourceContext
.Component
that started the dragpublic DragGestureEvent getTrigger()
DragGestureEvent
that initially triggered the drag.public int getSourceActions()
DnDConstants
that
represent the set of drop actions supported by the drag source for the
drag operation associated with this DragSourceContext
.public void setCursor(Cursor c)
Cursor
. If the specified Cursor
is null
, the default drag cursor behavior is
activated for this drag operation, otherwise it is deactivated.c
- the initial Cursor
for this drag operation,
or null
for the default cursor handling;
see class
level documentation for more details
on the cursor handling during drag and droppublic Cursor getCursor()
Cursor
.
Cursor
public void addDragSourceListener(DragSourceListener dsl) throws TooManyListenersException
DragSourceListener
to this
DragSourceContext
if one has not already been added.
If a DragSourceListener
already exists,
this method throws a TooManyListenersException
.
dsl
- the DragSourceListener
to add.
Note that while null
is not prohibited,
it is not acceptable as a parameter.
TooManyListenersException
- if
a DragSourceListener
has already been addedpublic void removeDragSourceListener(DragSourceListener dsl)
DragSourceListener
from this DragSourceContext
.dsl
- the DragSourceListener
to remove;
note that while null
is not prohibited,
it is not acceptable as a parameterpublic void transferablesFlavorsChanged()
Transferable
's
DataFlavor
s have changed.public void dragEnter(DragSourceDragEvent dsde)
dragEnter
on the
DragSourceListener
s registered with this
DragSourceContext
and with the associated
DragSource
, and passes them the specified
DragSourceDragEvent
.dragEnter
in interface DragSourceListener
dsde
- the DragSourceDragEvent
public void dragOver(DragSourceDragEvent dsde)
dragOver
on the
DragSourceListener
s registered with this
DragSourceContext
and with the associated
DragSource
, and passes them the specified
DragSourceDragEvent
.dragOver
in interface DragSourceListener
dsde
- the DragSourceDragEvent
public void dragExit(DragSourceEvent dse)
dragExit
on the
DragSourceListener
s registered with this
DragSourceContext
and with the associated
DragSource
, and passes them the specified
DragSourceEvent
.dragExit
in interface DragSourceListener
dse
- the DragSourceEvent
public void dropActionChanged(DragSourceDragEvent dsde)
dropActionChanged
on the
DragSourceListener
s registered with this
DragSourceContext
and with the associated
DragSource
, and passes them the specified
DragSourceDragEvent
.dropActionChanged
in interface DragSourceListener
dsde
- the DragSourceDragEvent
public void dragDropEnd(DragSourceDropEvent dsde)
dragDropEnd
on the
DragSourceListener
s registered with this
DragSourceContext
and with the associated
DragSource
, and passes them the specified
DragSourceDropEvent
.dragDropEnd
in interface DragSourceListener
dsde
- the DragSourceDropEvent
public void dragMouseMoved(DragSourceDragEvent dsde)
dragMouseMoved
on the
DragSourceMotionListener
s registered with the
DragSource
associated with this
DragSourceContext
, and them passes the specified
DragSourceDragEvent
.dragMouseMoved
in interface DragSourceMotionListener
dsde
- the DragSourceDragEvent
public Transferable getTransferable()
Transferable
associated with
this DragSourceContext
.Transferable
protected void updateCurrentCursor(int sourceAct, int targetAct, int status)
sourceAct
- the actions supported by the drag sourcetargetAct
- the drop target actionstatus
- one of the fields DEFAULT
,
ENTER
, OVER
,
CHANGED
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