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
* {@linkplain DragSourceListener DragSourceListeners}
* and {@linkplain DragSourceMotionListener DragSourceMotionListeners}, and providing the
* {@link 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 {@link DragSourceContextPeer} instance)
* created by the {@link 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, {@code DragSourceContext} sets the cursor as appropriate * for the current state of the drag and drop operation. For example, if * the user has chosen {@linkplain DnDConstants#ACTION_MOVE 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 {@link #setCursor} 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 {@code DragSource} events and calling the {@code setCursor()} method.
* Alternatively, you can provide custom cursor behavior by providing
* custom implementations of the {@code DragSource}
* and the {@code DragSourceContext} classes.
*
* @see DragSourceListener
* @see DragSourceMotionListener
* @see DnDConstants
* @since 1.2
*/
public class DragSourceContext
implements DragSourceListener, DragSourceMotionListener, Serializable {
private static final long serialVersionUID = -115407898692194719L;
// used by updateCurrentCursor
/**
* An int used by updateCurrentCursor()
* indicating that the Cursor should change
* to the default (no drop) Cursor.
*/
protected static final int DEFAULT = 0;
/**
* An int used by updateCurrentCursor()
* indicating that the Cursor
* has entered a DropTarget.
*/
protected static final int ENTER = 1;
/**
* An int used by updateCurrentCursor()
* indicating that the Cursor is
* over a DropTarget.
*/
protected static final int OVER = 2;
/**
* An int used by updateCurrentCursor()
* indicating that the user operation has changed.
*/
protected static final int CHANGED = 3;
/**
* 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.
*
* If DragSourceContextPeer is null
* NullPointerException is thrown.
*
* If DragGestureEvent is null
* NullPointerException is thrown.
*
* If Cursor is null no exception is thrown and
* the default drag cursor behavior is activated for this drag operation.
*
* If Image is null no exception is thrown.
*
* If Image is not null and the offset is
* null NullPointerException is thrown.
*
* If Transferable is null
* NullPointerException is thrown.
*
* If DragSourceListener is null no exception
* is thrown.
*
* @param dscp the DragSourceContextPeer for this drag
* @param trigger the triggering event
* @param dragCursor the initial {@code Cursor} for this drag operation
* or {@code null} for the default cursor handling;
* see class level documentation
* for more details on the cursor handling mechanism during drag and drop
* @param dragImage the Image to drag (or null)
* @param offset the offset of the image origin from the hotspot at the
* instant of the triggering event
* @param t the Transferable
* @param dsl the DragSourceListener
*
* @throws IllegalArgumentException if the Component associated
* with the trigger event is null.
* @throws IllegalArgumentException if the DragSource for the
* trigger event is null.
* @throws IllegalArgumentException if the drag action for the
* trigger event is DnDConstants.ACTION_NONE.
* @throws IllegalArgumentException if the source actions for the
* DragGestureRecognizer associated with the trigger
* event are equal to DnDConstants.ACTION_NONE.
* @throws NullPointerException if dscp, trigger, or t are null, or
* if dragImage is non-null and offset is null
*/
public DragSourceContext(DragSourceContextPeer dscp,
DragGestureEvent trigger, Cursor dragCursor,
Image dragImage, Point offset, Transferable t,
DragSourceListener dsl) {
if (dscp == null) {
throw new NullPointerException("DragSourceContextPeer");
}
if (trigger == null) {
throw new NullPointerException("Trigger");
}
if (trigger.getDragSource() == null) {
throw new IllegalArgumentException("DragSource");
}
if (trigger.getComponent() == null) {
throw new IllegalArgumentException("Component");
}
if (trigger.getSourceAsDragGestureRecognizer().getSourceActions() ==
DnDConstants.ACTION_NONE) {
throw new IllegalArgumentException("source actions");
}
if (trigger.getDragAction() == DnDConstants.ACTION_NONE) {
throw new IllegalArgumentException("no drag action");
}
if (t == null) {
throw new NullPointerException("Transferable");
}
if (dragImage != null && offset == null) {
throw new NullPointerException("offset");
}
peer = dscp;
this.trigger = trigger;
cursor = dragCursor;
transferable = t;
listener = dsl;
sourceActions =
trigger.getSourceAsDragGestureRecognizer().getSourceActions();
useCustomCursor = (dragCursor != null);
updateCurrentCursor(trigger.getDragAction(), getSourceActions(), DEFAULT);
}
/**
* Returns the DragSource
* that instantiated this DragSourceContext.
*
* @return the DragSource that
* instantiated this DragSourceContext
*/
public DragSource getDragSource() { return trigger.getDragSource(); }
/**
* Returns the Component associated with this
* DragSourceContext.
*
* @return the Component that started the drag
*/
public Component getComponent() { return trigger.getComponent(); }
/**
* Returns the DragGestureEvent
* that initially triggered the drag.
*
* @return the Event that triggered the drag
*/
public DragGestureEvent getTrigger() { return trigger; }
/**
* 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.
*
* @return the drop actions supported by the drag source
*/
public int getSourceActions() {
return sourceActions;
}
/**
* Sets the cursor for this drag operation to the specified
* Cursor. If the specified Cursor
* is null, the default drag cursor behavior is
* activated for this drag operation, otherwise it is deactivated.
*
* @param c the initial {@code Cursor} for this drag operation,
* or {@code null} for the default cursor handling;
* see {@linkplain Cursor class
* level documentation} for more details
* on the cursor handling during drag and drop
*
*/
public synchronized void setCursor(Cursor c) {
useCustomCursor = (c != null);
setCursorImpl(c);
}
/**
* Returns the current drag Cursor.
*
* @return the current drag Cursor
*/
public Cursor getCursor() { return cursor; }
/**
* Add a DragSourceListener to this
* DragSourceContext if one has not already been added.
* If a DragSourceListener already exists,
* this method throws a TooManyListenersException.
*
* @param dsl the DragSourceListener to add.
* Note that while null is not prohibited,
* it is not acceptable as a parameter.
*
* @throws TooManyListenersException if
* a DragSourceListener has already been added
*/
public synchronized void addDragSourceListener(DragSourceListener dsl) throws TooManyListenersException {
if (dsl == null) return;
if (equals(dsl)) throw new IllegalArgumentException("DragSourceContext may not be its own listener");
if (listener != null)
throw new TooManyListenersException();
else
listener = dsl;
}
/**
* Removes the specified DragSourceListener
* from this DragSourceContext.
*
* @param dsl the DragSourceListener to remove;
* note that while null is not prohibited,
* it is not acceptable as a parameter
*/
public synchronized void removeDragSourceListener(DragSourceListener dsl) {
if (listener != null && listener.equals(dsl)) {
listener = null;
} else
throw new IllegalArgumentException();
}
/**
* Notifies the peer that the Transferable's
* DataFlavors have changed.
*/
public void transferablesFlavorsChanged() {
if (peer != null) peer.transferablesFlavorsChanged();
}
/**
* Calls dragEnter on the
* DragSourceListeners registered with this
* DragSourceContext and with the associated
* DragSource, and passes them the specified
* DragSourceDragEvent.
*
* @param dsde the DragSourceDragEvent
*/
public void dragEnter(DragSourceDragEvent dsde) {
DragSourceListener dsl = listener;
if (dsl != null) {
dsl.dragEnter(dsde);
}
getDragSource().processDragEnter(dsde);
updateCurrentCursor(getSourceActions(), dsde.getTargetActions(), ENTER);
}
/**
* Calls dragOver on the
* DragSourceListeners registered with this
* DragSourceContext and with the associated
* DragSource, and passes them the specified
* DragSourceDragEvent.
*
* @param dsde the DragSourceDragEvent
*/
public void dragOver(DragSourceDragEvent dsde) {
DragSourceListener dsl = listener;
if (dsl != null) {
dsl.dragOver(dsde);
}
getDragSource().processDragOver(dsde);
updateCurrentCursor(getSourceActions(), dsde.getTargetActions(), OVER);
}
/**
* Calls dragExit on the
* DragSourceListeners registered with this
* DragSourceContext and with the associated
* DragSource, and passes them the specified
* DragSourceEvent.
*
* @param dse the DragSourceEvent
*/
public void dragExit(DragSourceEvent dse) {
DragSourceListener dsl = listener;
if (dsl != null) {
dsl.dragExit(dse);
}
getDragSource().processDragExit(dse);
updateCurrentCursor(DnDConstants.ACTION_NONE, DnDConstants.ACTION_NONE, DEFAULT);
}
/**
* Calls dropActionChanged on the
* DragSourceListeners registered with this
* DragSourceContext and with the associated
* DragSource, and passes them the specified
* DragSourceDragEvent.
*
* @param dsde the DragSourceDragEvent
*/
public void dropActionChanged(DragSourceDragEvent dsde) {
DragSourceListener dsl = listener;
if (dsl != null) {
dsl.dropActionChanged(dsde);
}
getDragSource().processDropActionChanged(dsde);
updateCurrentCursor(getSourceActions(), dsde.getTargetActions(), CHANGED);
}
/**
* Calls dragDropEnd on the
* DragSourceListeners registered with this
* DragSourceContext and with the associated
* DragSource, and passes them the specified
* DragSourceDropEvent.
*
* @param dsde the DragSourceDropEvent
*/
public void dragDropEnd(DragSourceDropEvent dsde) {
DragSourceListener dsl = listener;
if (dsl != null) {
dsl.dragDropEnd(dsde);
}
getDragSource().processDragDropEnd(dsde);
}
/**
* Calls dragMouseMoved on the
* DragSourceMotionListeners registered with the
* DragSource associated with this
* DragSourceContext, and them passes the specified
* DragSourceDragEvent.
*
* @param dsde the DragSourceDragEvent
* @since 1.4
*/
public void dragMouseMoved(DragSourceDragEvent dsde) {
getDragSource().processDragMouseMoved(dsde);
}
/**
* Returns the Transferable associated with
* this DragSourceContext.
*
* @return the Transferable
*/
public Transferable getTransferable() { return transferable; }
/**
* 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.
*
* @param sourceAct the actions supported by the drag source
* @param targetAct the drop target action
* @param status one of the fields DEFAULT,
* ENTER, OVER,
* CHANGED
*/
protected synchronized void updateCurrentCursor(int sourceAct, int targetAct, int status) {
// if the cursor has been previously set then dont do any defaults
// processing.
if (useCustomCursor) {
return;
}
// do defaults processing
Cursor c = null;
switch (status) {
default:
targetAct = DnDConstants.ACTION_NONE;
case ENTER:
case OVER:
case CHANGED:
int ra = sourceAct & targetAct;
if (ra == DnDConstants.ACTION_NONE) { // no drop possible
if ((sourceAct & DnDConstants.ACTION_LINK) == DnDConstants.ACTION_LINK)
c = DragSource.DefaultLinkNoDrop;
else if ((sourceAct & DnDConstants.ACTION_MOVE) == DnDConstants.ACTION_MOVE)
c = DragSource.DefaultMoveNoDrop;
else
c = DragSource.DefaultCopyNoDrop;
} else { // drop possible
if ((ra & DnDConstants.ACTION_LINK) == DnDConstants.ACTION_LINK)
c = DragSource.DefaultLinkDrop;
else if ((ra & DnDConstants.ACTION_MOVE) == DnDConstants.ACTION_MOVE)
c = DragSource.DefaultMoveDrop;
else
c = DragSource.DefaultCopyDrop;
}
}
setCursorImpl(c);
}
private void setCursorImpl(Cursor c) {
if (cursor == null || !cursor.equals(c)) {
cursor = c;
if (peer != null) peer.setCursor(cursor);
}
}
/**
* Serializes this DragSourceContext. This method first
* performs default serialization. Next, this object's
* Transferable is written out if and only if it can be
* serialized. If not, null is written instead. In this case,
* a DragSourceContext created from the resulting deserialized
* stream will contain a dummy Transferable which supports no
* DataFlavors. Finally, this object's
* DragSourceListener is written out if and only if it can be
* serialized. If not, null is written instead.
*
* @serialData The default serializable fields, in alphabetical order,
* followed by either a Transferable instance, or
* null, followed by either a
* DragSourceListener instance, or
* null.
* @since 1.4
*/
private void writeObject(ObjectOutputStream s) throws IOException {
s.defaultWriteObject();
s.writeObject(SerializationTester.test(transferable)
? transferable : null);
s.writeObject(SerializationTester.test(listener)
? listener : null);
}
/**
* Deserializes this DragSourceContext. This method first
* performs default deserialization for all non-transient
* fields. This object's Transferable and
* DragSourceListener are then deserialized as well by using
* the next two objects in the stream. If the resulting
* Transferable is null, this object's
* Transferable is set to a dummy Transferable
* which supports no DataFlavors.
*
* @since 1.4
*/
private void readObject(ObjectInputStream s)
throws ClassNotFoundException, IOException
{
s.defaultReadObject();
transferable = (Transferable)s.readObject();
listener = (DragSourceListener)s.readObject();
// Implementation assumes 'transferable' is never null.
if (transferable == null) {
if (emptyTransferable == null) {
emptyTransferable = new Transferable() {
public DataFlavor[] getTransferDataFlavors() {
return new DataFlavor[0];
}
public boolean isDataFlavorSupported(DataFlavor flavor)
{
return false;
}
public Object getTransferData(DataFlavor flavor)
throws UnsupportedFlavorException
{
throw new UnsupportedFlavorException(flavor);
}
};
}
transferable = emptyTransferable;
}
}
private static Transferable emptyTransferable;
/*
* fields
*/
private transient DragSourceContextPeer peer;
/**
* The event which triggered the start of the drag.
*
* @serial
*/
private DragGestureEvent trigger;
/**
* The current drag cursor.
*
* @serial
*/
private Cursor cursor;
private transient Transferable transferable;
private transient DragSourceListener listener;
/**
* true if the custom drag cursor is used instead of the
* default one.
*
* @serial
*/
private boolean useCustomCursor;
/**
* A bitwise mask of DnDConstants that represents the set of
* drop actions supported by the drag source for the drag operation associated
* with this DragSourceContext.
*
* @serial
*/
private final int sourceActions;
}