com.sun.jna.platform.dnd
Class DragHandler

java.lang.Object
  com.sun.jna.platform.dnd.DragHandler

All Implemented Interfaces:

DragGestureListener, DragSourceListener, DragSourceMotionListener, EventListener

public abstract class DragHandler
extends Object
implements DragSourceListener, DragSourceMotionListener, DragGestureListener

Provides simplified drag handling for a component. Usage:

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

• Supports painting an arbitrary Icon with transparency to represent the item being dragged (restricted to the Window of the drag source if the platform doesn't support drag images).
• Disallow starting a drag if the user requests an unsupported action.
• Adjusts the cursor on drags with no modifier for which the default action is disallowed but where one or more non-default actions are allowed, e.g. a drag (with no modifiers) to a target which supports "link" should change the cursor to "link" (prior to 1.6, the JRE behavior is to display a "not allowed" cursor, even though the action actually depends on how the drop target responds). The bug is fixed in java 1.6.
• Disallow drops to targets if the non-default (user-requested) action is not supported by the target, e.g. the user requests a "copy" when the target only supports "move". This is generally the responsibility of the drop handler, which decides whether or not to accept a drag. The DragHandler provides static modifier state information since the drop handler doesn't have access to it.

MAX_GHOST_SIZE

public static final Dimension MAX_GHOST_SIZE

Default maximum size for ghosted images.

DEFAULT_GHOST_ALPHA

public static final float DEFAULT_GHOST_ALPHA

Default transparency for ghosting.

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Constant Field Values

UNKNOWN_MODIFIERS

public static final int UNKNOWN_MODIFIERS

getModifiers() returns this value when the current modifiers state is unknown.

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Constant Field Values

UNKNOWN_TRANSFERABLE

public static final Transferable UNKNOWN_TRANSFERABLE

getTransferable(java.awt.dnd.DropTargetEvent) returns this value when the current Transferable is unknown.

MOVE

protected static final int MOVE

Convenience to reference DnDConstants.ACTION_MOVE.

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Constant Field Values

COPY

protected static final int COPY

Convenience to reference DnDConstants.ACTION_COPY.

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Constant Field Values

LINK

protected static final int LINK

Convenience to reference DnDConstants.ACTION_LINK.

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Constant Field Values

NONE

protected static final int NONE

Convenience to reference DnDConstants.ACTION_NONE.

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Constant Field Values

MOVE_MASK

static final int MOVE_MASK

Modifier mask for a user-requested move.

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Constant Field Values

OSX

static final boolean OSX

COPY_MASK

static final int COPY_MASK

Modifier mask for a user-requested copy.

LINK_MASK

static final int LINK_MASK

Modifier mask for a user-requested link.

KEY_MASK

static final int KEY_MASK

Modifier mask for any user-requested action.

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Constant Field Values

DragHandler

protected DragHandler(Component dragSource,
                      int actions)

Enable drags from the given component, supporting the actions in the given action mask.

getModifiers

static int getModifiers()

Used to communicate modifier state to DropHandler. Note that this field will only be accurate when a DragHandler in the same VM started the drag. Otherwise, UNKNOWN_MODIFIERS will be returned.

getTransferable

public static Transferable getTransferable(DropTargetEvent e)

Used to communicate the current Transferable during a drag, if available. Work around absence of access to the data when dragging pre-1.5.

canDrag

protected boolean canDrag(DragGestureEvent e)

Override to control whether a drag is started. The default implementation disallows the drag if the user is applying modifiers and the user-requested action is not supported.

setModifiers

protected void setModifiers(int mods)

Update the modifiers hint.

getTransferable

protected abstract Transferable getTransferable(DragGestureEvent e)

Override to provide an appropriate Transferable representing the data being dragged.

getDragIcon

protected Icon getDragIcon(DragGestureEvent e,
                           Point srcOffset)

Override this to provide a custom image. The Icon returned by this method by default is null, which results in no drag image.

Parameters:

srcOffset - set this to be the offset from the drag source component's upper left corner to the image's upper left corner. For example, when dragging a row from a list, the offset would be the row's bounding rectangle's (x,y) coordinate.

The default value is (0,0), so if unchanged, the image is will use the same origin as the drag source component.

dragStarted

protected void dragStarted(DragGestureEvent e)

Override to perform any decoration of the target at the start of a drag, if desired.

dragGestureRecognized

public void dragGestureRecognized(DragGestureEvent e)

Called when a user drag gesture is recognized. This method is responsible for initiating the drag operation.

Specified by:

dragGestureRecognized in interface DragGestureListener

scaleDragIcon

protected Icon scaleDragIcon(Icon icon,
                             Point imageOffset)

Reduce the size of the given drag icon, if appropriate. When using a smaller drag icon, we also need to adjust the cursor offset within the icon.

createDragImage

protected Image createDragImage(GraphicsConfiguration gc,
                                Icon icon)

Create an image from the given icon. The image is provided to the native handler if drag images are supported natively.

getCursorForAction

protected Cursor getCursorForAction(int actualAction)

getAcceptableDropAction

protected int getAcceptableDropAction(int targetActions)

Returns the first available action supported by source and target.

getDropAction

protected int getDropAction(DragSourceEvent ev)

Get the currently requested drop action.

adjustDropAction

protected int adjustDropAction(DragSourceEvent ev)

Pick a different drop action if the target doesn't support the current one and there are no modifiers.

updateCursor

protected void updateCursor(DragSourceEvent ev)

actionString

static String actionString(int action)

dragDropEnd

public void dragDropEnd(DragSourceDropEvent e)

Specified by:

dragDropEnd in interface DragSourceListener

dragEnter

public void dragEnter(DragSourceDragEvent e)

Specified by:

dragEnter in interface DragSourceListener

dragMouseMoved

public void dragMouseMoved(DragSourceDragEvent e)

Specified by:

dragMouseMoved in interface DragSourceMotionListener

dragOver

public void dragOver(DragSourceDragEvent e)

Specified by:

dragOver in interface DragSourceListener

dragExit

public void dragExit(DragSourceEvent e)

Specified by:

dragExit in interface DragSourceListener

dropActionChanged

public void dropActionChanged(DragSourceDragEvent e)

Specified by:

dropActionChanged in interface DragSourceListener