Package com.sun.jna.platform.dnd

Class 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().

    • Constructor Detail

      • DragHandler

        protected DragHandler​(Component dragSource,
                      int actions)
        Enable drags from the given component, supporting the actions in the given action mask.
        Parameters:
        dragSource - source of the drag.
        actions - actions which should be supported.

    • 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.
        Returns:
        Current drag modifiers.

      • 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.
        Parameters:
        e - event
        Returns:
        Transferable representation of the item being dragged.

      • 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.
        Parameters:
        e - event
        Returns:
        Whether to allow a drag

      • setModifiers

        protected void setModifiers​(int mods)
        Update the modifiers hint.
        Parameters:
        mods - Current modifiers

      • 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:
        e - event
        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.

        Returns:
        drag icon (defaults to none)

      • dragStarted

        protected void dragStarted​(DragGestureEvent e)
        Override to perform any decoration of the target at the start of a drag, if desired.
        Parameters:
        e - event

      • 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
        Parameters:
        e - event

      • scaleDragIcon

        protected Icon scaleDragIcon​(Icon icon,
                             Point imageOffset)
        Change the size of the given drag icon, if appropriate. When using a differently-sized drag icon, we also need to adjust the cursor offset within the icon.
        Parameters:
        icon - Icon to be scaled.
        imageOffset - Modified to account for the new icon's size.
        Returns:
        Scaled Icon, or the original if there was no change.

      • 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.
        Parameters:
        gc - current graphics configuration.
        icon - Icon on which to base the drag image.
        Returns:
        image based on the given icon.

      • getCursorForAction

        protected Cursor getCursorForAction​(int actualAction)

      • getAcceptableDropAction

        protected int getAcceptableDropAction​(int targetActions)
        Returns the first available action supported by source and target.
        Parameters:
        targetActions - current actions requested
        Returns:
        subset of actions supported based on the input

      • getDropAction

        protected int getDropAction​(DragSourceEvent ev)
        Get the currently requested drop action.
        Parameters:
        ev - event
        Returns:
        effective 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.
        Parameters:
        ev - event
        Returns:
        effective drop action

      • updateCursor

        protected void updateCursor​(DragSourceEvent ev)
        Hook to update the cursor on various DragSourceEvent updates.
        Parameters:
        ev - event

      • actionString

        static String actionString​(int action)