DragGestureRecognizer is an
* abstract base class for the specification
* of a platform-dependent listener that can be associated with a particular
* Component in order to
* identify platform-dependent drag initiating gestures.
*
* The appropriate DragGestureRecognizer
* subclass instance is obtained from the
* {@link DragSource} asssociated with
* a particular Component, or from the Toolkit object via its
* {@link java.awt.Toolkit#createDragGestureRecognizer createDragGestureRecognizer()}
* method.
*
* Once the DragGestureRecognizer
* is associated with a particular Component
* it will register the appropriate listener interfaces on that
* Component
* in order to track the input events delivered to the Component.
*
* Once the DragGestureRecognizer identifies a sequence of events
* on the Component as a drag initiating gesture, it will notify
* its unicast DragGestureListener by
* invoking its
* {@link java.awt.dnd.DragGestureListener#dragGestureRecognized gestureRecognized()}
* method.
*
* When a concrete DragGestureRecognizer
* instance detects a drag initiating
* gesture on the Component it is associated with,
* it fires a {@link DragGestureEvent} to
* the DragGestureListener registered on
* its unicast event source for DragGestureListener
* events. This DragGestureListener is responsible
* for causing the associated
* DragSource to start the Drag and Drop operation (if
* appropriate).
*
* @author Laurence P. G. Cable
* @see java.awt.dnd.DragGestureListener
* @see java.awt.dnd.DragGestureEvent
* @see java.awt.dnd.DragSource
*/
public abstract class DragGestureRecognizer implements Serializable {
private static final long serialVersionUID = 8996673345831063337L;
/**
* Construct a new DragGestureRecognizer
* given the DragSource to be used
* in this Drag and Drop operation, the Component
* this DragGestureRecognizer should "observe"
* for drag initiating gestures, the action(s) supported
* for this Drag and Drop operation, and the
* DragGestureListener to notify
* once a drag initiating gesture has been detected.
*
* @param ds the DragSource this
* DragGestureRecognizer
* will use to process the Drag and Drop operation
*
* @param c the Component
* this DragGestureRecognizer
* should "observe" the event stream to,
* in order to detect a drag initiating gesture.
* If this value is null, the
* DragGestureRecognizer
* is not associated with any Component.
*
* @param sa the set (logical OR) of the
* DnDConstants
* that this Drag and Drop operation will support
*
* @param dgl the DragGestureRecognizer
* to notify when a drag gesture is detected
*
* @throws IllegalArgumentException
* if ds is null.
*/
protected DragGestureRecognizer(DragSource ds, Component c, int sa, DragGestureListener dgl) {
super();
if (ds == null) throw new IllegalArgumentException("null DragSource");
dragSource = ds;
component = c;
sourceActions = sa & (DnDConstants.ACTION_COPY_OR_MOVE | DnDConstants.ACTION_LINK);
try {
if (dgl != null) addDragGestureListener(dgl);
} catch (TooManyListenersException tmle) {
// cant happen ...
}
}
/**
* Construct a new DragGestureRecognizer
* given the DragSource to be used in this
* Drag and Drop
* operation, the Component this
* DragGestureRecognizer should "observe"
* for drag initiating gestures, and the action(s)
* supported for this Drag and Drop operation.
*
* @param ds the DragSource this
* DragGestureRecognizer will use to
* process the Drag and Drop operation
*
* @param c the Component this
* DragGestureRecognizer should "observe" the event
* stream to, in order to detect a drag initiating gesture.
* If this value is null, the
* DragGestureRecognizer
* is not associated with any Component.
*
* @param sa the set (logical OR) of the DnDConstants
* that this Drag and Drop operation will support
*
* @throws IllegalArgumentException
* if ds is null.
*/
protected DragGestureRecognizer(DragSource ds, Component c, int sa) {
this(ds, c, sa, null);
}
/**
* Construct a new DragGestureRecognizer
* given the DragSource to be used
* in this Drag and Drop operation, and
* the Component this
* DragGestureRecognizer
* should "observe" for drag initiating gestures.
*
* @param ds the DragSource this
* DragGestureRecognizer
* will use to process the Drag and Drop operation
*
* @param c the Component
* this DragGestureRecognizer
* should "observe" the event stream to,
* in order to detect a drag initiating gesture.
* If this value is null,
* the DragGestureRecognizer
* is not associated with any Component.
*
* @throws IllegalArgumentException
* if ds is null.
*/
protected DragGestureRecognizer(DragSource ds, Component c) {
this(ds, c, DnDConstants.ACTION_NONE);
}
/**
* Construct a new DragGestureRecognizer
* given the DragSource to be used in this
* Drag and Drop operation.
*
* @param ds the DragSource this
* DragGestureRecognizer will
* use to process the Drag and Drop operation
*
* @throws IllegalArgumentException
* if ds is null.
*/
protected DragGestureRecognizer(DragSource ds) {
this(ds, null);
}
/**
* register this DragGestureRecognizer's Listeners with the Component
*
* subclasses must override this method
*/
protected abstract void registerListeners();
/**
* unregister this DragGestureRecognizer's Listeners with the Component
*
* subclasses must override this method
*/
protected abstract void unregisterListeners();
/**
* This method returns the DragSource
* this DragGestureRecognizer
* will use in order to process the Drag and Drop
* operation.
*
* @return the DragSource
*/
public DragSource getDragSource() { return dragSource; }
/**
* This method returns the Component
* that is to be "observed" by the
* DragGestureRecognizer
* for drag initiating gestures.
*
* @return The Component this DragGestureRecognizer * is associated with */ public synchronized Component getComponent() { return component; } /** * set the Component that the DragGestureRecognizer is associated with * * registerListeners() and unregisterListeners() are called as a side * effect as appropriate. *
* @param c The Component or null
*/
public synchronized void setComponent(Component c) {
if (component != null && dragGestureListener != null)
unregisterListeners();
component = c;
if (component != null && dragGestureListener != null)
registerListeners();
}
/**
* This method returns an int representing the
* type of action(s) this Drag and Drop
* operation will support.
*
* @return the currently permitted source action(s) */ public synchronized int getSourceActions() { return sourceActions; } /** * This method sets the permitted source drag action(s) * for this Drag and Drop operation. *
* @param actions the permitted source drag action(s) */ public synchronized void setSourceActions(int actions) { sourceActions = actions & (DnDConstants.ACTION_COPY_OR_MOVE | DnDConstants.ACTION_LINK); } /** * This method returns the first event in the * series of events that initiated * the Drag and Drop operation. *
* @return the initial event that triggered the drag gesture
*/
public InputEvent getTriggerEvent() { return events.isEmpty() ? null : (InputEvent)events.get(0); }
/**
* Reset the Recognizer, if its currently recognizing a gesture, ignore
* it.
*/
public void resetRecognizer() { events.clear(); }
/**
* Register a new DragGestureListener.
*
* @param dgl the DragGestureListener to register
* with this DragGestureRecognizer.
*
* @throws java.util.TooManyListenersException if a
* DragGestureListener has already been added.
*/
public synchronized void addDragGestureListener(DragGestureListener dgl) throws TooManyListenersException {
if (dragGestureListener != null)
throw new TooManyListenersException();
else {
dragGestureListener = dgl;
if (component != null) registerListeners();
}
}
/**
* unregister the current DragGestureListener
*
* @param dgl the DragGestureListener to unregister
* from this DragGestureRecognizer
*
* @throws IllegalArgumentException if
* dgl is not (equal to) the currently registered DragGestureListener.
*/
public synchronized void removeDragGestureListener(DragGestureListener dgl) {
if (dragGestureListener == null || !dragGestureListener.equals(dgl))
throw new IllegalArgumentException();
else {
dragGestureListener = null;
if (component != null) unregisterListeners();
}
}
/**
* Notify the DragGestureListener that a Drag and Drop initiating
* gesture has occurred. Then reset the state of the Recognizer.
*
* @param dragAction The action initially selected by the users gesture * @param p The point (in Component coords) where the gesture originated */ protected synchronized void fireDragGestureRecognized(int dragAction, Point p) { try { if (dragGestureListener != null) { dragGestureListener.dragGestureRecognized(new DragGestureEvent(this, dragAction, p, events)); } } finally { events.clear(); } } /** * Listeners registered on the Component by this Recognizer shall record * all Events that are recognized as part of the series of Events that go * to comprise a Drag and Drop initiating gesture via this API. *
* This method is used by a DragGestureRecognizer
* implementation to add an InputEvent
* subclass (that it believes is one in a series
* of events that comprise a Drag and Drop operation)
* to the array of events that this
* DragGestureRecognizer maintains internally.
*
* @param awtie the InputEvent
* to add to this DragGestureRecognizer's
* internal array of events. Note that null
* is not a valid value, and will be ignored.
*/
protected synchronized void appendEvent(InputEvent awtie) {
events.add(awtie);
}
/**
* Serializes this DragGestureRecognizer. This method first
* performs default serialization. Then, this object's
* DragGestureListener 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 DragGestureListener, or
* null.
* @since 1.4
*/
private void writeObject(ObjectOutputStream s) throws IOException {
s.defaultWriteObject();
s.writeObject(SerializationTester.test(dragGestureListener)
? dragGestureListener : null);
}
/**
* Deserializes this DragGestureRecognizer. This method first
* performs default deserialization for all non-transient
* fields. This object's DragGestureListener is then
* deserialized as well by using the next object in the stream.
*
* @since 1.4
*/
private void readObject(ObjectInputStream s)
throws ClassNotFoundException, IOException
{
s.defaultReadObject();
dragGestureListener = (DragGestureListener)s.readObject();
}
/*
* fields
*/
/**
* The DragSource
* associated with this
* DragGestureRecognizer.
*
* @serial
*/
protected DragSource dragSource;
/**
* The Component
* associated with this DragGestureRecognizer.
*
* @serial
*/
protected Component component;
/**
* The DragGestureListener
* associated with this DragGestureRecognizer.
*/
protected transient DragGestureListener dragGestureListener;
/**
* An int representing
* the type(s) of action(s) used
* in this Drag and Drop operation.
*
* @serial
*/
protected int sourceActions;
/**
* The list of events (in order) that
* the DragGestureRecognizer
* "recognized" as a "gesture" that triggers a drag.
*
* @serial
*/
protected ArrayList