Package com.sun.jna.platform.dnd

Class DropHandler

java.lang.Object

com.sun.jna.platform.dnd.DropHandler

All Implemented Interfaces:

DropTargetListener, EventListener

public abstract class DropHandler
extends Object
implements DropTargetListener

Provides simplified drop handling for a component. Usage:

 int actions = DnDConstants.MOVE_OR_COPY;
 Component component = ...;
 DropHandler handler = new DropHandler(component, actions);
 

• Accept drops where the action is the default (i.e. no modifiers) but the intersection of source and target actions is not the default. Doing so allows the source to adjust the cursor appropriately.
• Refuse drops where the user modifiers request an action that is not supported (this works for all cases except when the drag source is not a DragHandler and the user explicitly requests a MOVE operation; this is indistinguishable from a drag with no modifiers unless we have access to the key modifiers, which DragHandler provides).
• Drops may be refused based on data flavor, location, intended drop action, or any combination of those, by overriding canDrop(java.awt.dnd.DropTargetEvent, int, java.awt.Point).
• Custom decoration of the drop area may be performed in paintDropTarget(DropTargetEvent, int, Point) or by providing a DropTargetPainter.

The method getDropAction(DropTargetEvent) follows these steps to determine the appropriate action (if any).

• isSupported(DataFlavor[]) determines if there are any supported flavors
• getDropActionsForFlavors(DataFlavor[]) reduces the supported actions based on available flavors. For instance, a text field for file paths might support DnDConstants.ACTION_COPY_OR_MOVE on a plain string, but DnDConstants.ACTION_LINK might be the only action supported on a file.
• getDropAction(DropTargetEvent, int, int, int) relax the action if it's the default, or restrict it for user requested actions.
• canDrop(DropTargetEvent, int, Point) change the action based on the location in the drop target component, or any other criteria.

Override drop(DropTargetDropEvent, int) to handle the drop. You should invoke DropTargetDropEvent.dropComplete(boolean) as soon as the Transferable data is obtained, to avoid making the DnD operation look suspended.

Author:

twall

See Also:

DragHandler

Constructor Summary

Constructors

Constructor	Description
DropHandler(Component c, int acceptedActions)	Create a handler that allows the given set of actions.
DropHandler(Component c, int acceptedActions, DataFlavor[] acceptedFlavors)	Enable handling of drops, indicating what actions and flavors are acceptable.
DropHandler(Component c, int acceptedActions, DataFlavor[] acceptedFlavors, DropTargetPainter painter)	Enable handling of drops, indicating what actions and flavors are acceptable, and providing a painter for drop target feedback.

Method Summary

Modifier and Type	Method	Description
protected int	acceptOrReject(DropTargetDragEvent e)	Accept or reject the drag represented by the given event.
protected boolean	canDrop(DropTargetEvent e, int action, Point location)	Indicate whether the given drop action is acceptable at the given location.
void	dragEnter(DropTargetDragEvent e)
void	dragExit(DropTargetEvent e)
void	dragOver(DropTargetDragEvent e)
void	drop(DropTargetDropEvent e)	Indicates the user has initiated a drop.
protected abstract void	drop(DropTargetDropEvent e, int action)	Handle an incoming drop with the given action.
void	dropActionChanged(DropTargetDragEvent e)
protected int	getDropAction(DropTargetEvent e)	Calculate the effective action.
protected int	getDropAction(DropTargetEvent e, int currentAction, int sourceActions, int acceptedActions)
protected int	getDropActionsForFlavors(DataFlavor[] dataFlavors)	Indicate the actions available for the given list of data flavors.
protected DropTarget	getDropTarget()
boolean	isActive()
protected boolean	isSupported(DataFlavor[] flavors)	Return whether any of the flavors in the given list are accepted.
protected boolean	modifiersActive(int dropAction)	Returns whether there are key modifiers active , or false if they can't be determined.
protected void	paintDropTarget(DropTargetEvent e, int action, Point location)	Update the appearance of the target component.
void	setActive(boolean active)	Set whether this handler (and thus its drop target) will accept any drops.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

DropHandler

public DropHandler(Component c,
                   int acceptedActions)

Create a handler that allows the given set of actions. If using this constructor, you will need to override isSupported(java.awt.datatransfer.DataFlavor[]) to indicate which data flavors are allowed.

Parameters:

c - target component

acceptedActions - accepted actions

DropHandler

public DropHandler(Component c,
                   int acceptedActions,
                   DataFlavor[] acceptedFlavors)

Enable handling of drops, indicating what actions and flavors are acceptable.

Parameters:

c - The component to receive drops

acceptedActions - Allowed actions for drops

acceptedFlavors - Allowed data flavors for drops

See Also:

isSupported(java.awt.datatransfer.DataFlavor[])

DropHandler

public DropHandler(Component c,
                   int acceptedActions,
                   DataFlavor[] acceptedFlavors,
                   DropTargetPainter painter)

Enable handling of drops, indicating what actions and flavors are acceptable, and providing a painter for drop target feedback.

Parameters:

c - The component to receive drops

acceptedActions - Allowed actions for drops

acceptedFlavors - Allowed data flavors for drops

painter - Painter to handle drop target feedback

See Also:

paintDropTarget(java.awt.dnd.DropTargetEvent, int, java.awt.Point)

Method Detail

getDropTarget

protected DropTarget getDropTarget()

isActive

public boolean isActive()

Returns:

Whether this drop target is active.

setActive

public void setActive(boolean active)

Set whether this handler (and thus its drop target) will accept any drops.

Parameters:

active - whether this handler should accept drops.

getDropActionsForFlavors

protected int getDropActionsForFlavors(DataFlavor[] dataFlavors)

Indicate the actions available for the given list of data flavors. Override this method if the acceptable drop actions depend on the currently available DataFlavor. The default returns the accepted actions passed into the constructor.

Parameters:

dataFlavors - currently available flavors

Returns:

currently acceptable actions.

See Also:

getDropAction(DropTargetEvent, int, int, int), canDrop(DropTargetEvent, int, Point)

getDropAction

protected int getDropAction(DropTargetEvent e)

Calculate the effective action. The default implementation checks whether any DataFlavors are supported, and if so, will change the current action from DnDConstants.ACTION_NONE to something in common between the source and destination. Refuse user-requested actions if they are not supported (rather than silently accepting a non-user-requested action, which is the Java's DnD default behavior). The drop action is forced to DnDConstants.ACTION_NONE if there is no supported data flavor.

Parameters:

e - DropTargetEvent

Returns:

effective drop action

See Also:

isSupported(DataFlavor[]), getDropActionsForFlavors(java.awt.datatransfer.DataFlavor[]), getDropAction(DropTargetEvent, int, int, int), canDrop(DropTargetEvent, int, Point)

getDropAction

protected int getDropAction(DropTargetEvent e,
                            int currentAction,
                            int sourceActions,
                            int acceptedActions)

modifiersActive

protected boolean modifiersActive(int dropAction)

Returns whether there are key modifiers active , or false if they can't be determined. We use the DragHandler hint, if available, or fall back to whether the drop action is other than the default (move).

Parameters:

dropAction - requested action.

Returns:

whether any modifiers are active.

acceptOrReject

protected int acceptOrReject(DropTargetDragEvent e)

Accept or reject the drag represented by the given event. Returns the action determined by getDropAction(DropTargetEvent).

Parameters:

e - event

Returns:

resulting action

dragEnter

public void dragEnter(DropTargetDragEvent e)

Specified by:

dragEnter in interface DropTargetListener

dragOver

public void dragOver(DropTargetDragEvent e)

Specified by:

dragOver in interface DropTargetListener

dragExit

public void dragExit(DropTargetEvent e)

Specified by:

dragExit in interface DropTargetListener

dropActionChanged

public void dropActionChanged(DropTargetDragEvent e)

Specified by:

dropActionChanged in interface DropTargetListener

drop

public void drop(DropTargetDropEvent e)

Indicates the user has initiated a drop. The default performs all standard drop validity checking and handling, then invokes drop(DropTargetDropEvent,int) if the drop looks acceptable.

Specified by:

drop in interface DropTargetListener

isSupported

protected boolean isSupported(DataFlavor[] flavors)

Return whether any of the flavors in the given list are accepted. The list is compared against the accepted list provided in the constructor.

Parameters:

flavors - list of transfer flavors to check

Returns:

whether any of the given flavors are supported

paintDropTarget

protected void paintDropTarget(DropTargetEvent e,
                               int action,
                               Point location)

Update the appearance of the target component. Normally the decoration should be painted only if the event is an instance of DropTargetDragEvent with an action that is not DragHandler.NONE. Otherwise the decoration should be removed or hidden.

For an easy way to highlight the drop target, consider using a single instance of AbstractComponentDecorator and moving it according to the intended drop location.

Parameters:

e - The drop target event

action - The action for the drop

location - The intended drop location, or null if there is none

canDrop

protected boolean canDrop(DropTargetEvent e,
                          int action,
                          Point location)

Indicate whether the given drop action is acceptable at the given location. This method is the last check performed by getDropAction(DropTargetEvent). You may override this method to refuse drops on certain areas within the drop target component. The default always returns true.

Parameters:

e - event

action - requested action

location - requested drop location

Returns:

whether the drop is supported

drop

protected abstract void drop(DropTargetDropEvent e,
                             int action)
                      throws UnsupportedFlavorException,
                             IOException

Handle an incoming drop with the given action. The action passed in might be different from DropTargetDropEvent.getDropAction(), for instance, if there are no modifiers and the default action is not supported. Calling DropTargetDropEvent.dropComplete(boolean) is recommended as soon as the Transferable data is obtained; this allows the drag source to reset the cursor and any drag images which may be in effect.

Parameters:

e - event

action - requested drop type

Throws:

UnsupportedFlavorException - dropped item has no supported flavors

IOException - data access failure