DragHandler (JNA API)

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## 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.

NOTE: Fundamentally, the active action is determined by the drop handler in `DropTargetDragEvent.acceptDrag(int)`, but often client code simply relies on `DropTargetDragEvent.getDropAction()`.

Field Summary
`protected static int` | `COPY` Convenience to reference `DnDConstants.ACTION_COPY`.
`(package private) static int` | `COPY_MASK` Modifier mask for a user-requested copy.
`static float` | `DEFAULT_GHOST_ALPHA` Default transparency for ghosting.
`(package private) static int` | `KEY_MASK` Modifier mask for any user-requested action.
`protected static int` | `LINK` Convenience to reference `DnDConstants.ACTION_LINK`.
`(package private) static int` | `LINK_MASK` Modifier mask for a user-requested link.
`static Dimension` | `MAX_GHOST_SIZE` Default maximum size for ghosted images.
`protected static int` | `MOVE` Convenience to reference `DnDConstants.ACTION_MOVE`.
`(package private) static int` | `MOVE_MASK` Modifier mask for a user-requested move.
`protected static int` | `NONE` Convenience to reference `DnDConstants.ACTION_NONE`.
`(package private) static boolean` | `OSX`
`static int` | `UNKNOWN_MODIFIERS` `getModifiers()` returns this value when the current modifiers state is unknown.
`static Transferable` | `UNKNOWN_TRANSFERABLE` `getTransferable(java.awt.dnd.DropTargetEvent)` returns this value when the current `Transferable` is unknown.

Constructor Summary
`protected` | `DragHandler(Component dragSource, int actions)` Enable drags from the given component, supporting the actions in the given action mask.

Method Summary
`(package private) static String` | `actionString(int action)`
`protected int` | `adjustDropAction(DragSourceEvent ev)` Pick a different drop action if the target doesn't support the current one and there are no modifiers.
`protected boolean` | `canDrag(DragGestureEvent e)` Override to control whether a drag is started.
`protected Image` | `createDragImage(GraphicsConfiguration gc, Icon icon)` Create an image from the given icon.
`void` | `dragDropEnd(DragSourceDropEvent e)`
`void` | `dragEnter(DragSourceDragEvent e)`
`void` | `dragExit(DragSourceEvent e)`
`void` | `dragGestureRecognized(DragGestureEvent e)` Called when a user drag gesture is recognized.
`void` | `dragMouseMoved(DragSourceDragEvent e)`
`void` | `dragOver(DragSourceDragEvent e)`
`protected void` | `dragStarted(DragGestureEvent e)` Override to perform any decoration of the target at the start of a drag, if desired.
`void` | `dropActionChanged(DragSourceDragEvent e)`
`protected int` | `getAcceptableDropAction(int targetActions)` Returns the first available action supported by source and target.
`protected Cursor` | `getCursorForAction(int actualAction)`
`protected Icon` | `getDragIcon(DragGestureEvent e, Point srcOffset)` Override this to provide a custom image.
`protected int` | `getDropAction(DragSourceEvent ev)` Get the currently requested drop action.
`(package private) static int` | `getModifiers()` Used to communicate modifier state to `DropHandler`.
`protected abstract Transferable` | `getTransferable(DragGestureEvent e)` Override to provide an appropriate `Transferable` representing the data being dragged.
`static Transferable` | `getTransferable(DropTargetEvent e)` Used to communicate the current `Transferable` during a drag, if available.
`protected Icon` | `scaleDragIcon(Icon icon, Point imageOffset)` Reduce the size of the given drag icon, if appropriate.
`protected void` | `setModifiers(int mods)` Update the modifiers hint.
`protected void` | `updateCursor(DragSourceEvent ev)`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Field Detail

### 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.

  See Also:
    Constant Field Values

### UNKNOWN_MODIFIERS

    public static final int UNKNOWN_MODIFIERS

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

  See Also:
    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`.

  See Also:
    Constant Field Values

### COPY

    protected static final int COPY

  Convenience to reference `DnDConstants.ACTION_COPY`.

  See Also:
    Constant Field Values

### LINK

    protected static final int LINK

  Convenience to reference `DnDConstants.ACTION_LINK`.

  See Also:
    Constant Field Values

### NONE

    protected static final int NONE

  Convenience to reference `DnDConstants.ACTION_NONE`.

  See Also:
    Constant Field Values

### MOVE_MASK

    static final int MOVE_MASK

  Modifier mask for a user-requested move.

  See Also:
    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.

  See Also:
    Constant Field Values

Constructor Detail

### DragHandler

    protected DragHandler(Component dragSource,
                          int actions)

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

Method Detail

### 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`

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Copyright © 2007-2010 Timothy Wall. All Rights Reserved.