Module java.desktop
Package java.awt.dnd

Class DragSourceContext

  • All Implemented Interfaces:
    DragSourceListener, DragSourceMotionListener, Serializable, EventListener
    public class DragSourceContext
extends Object
implements DragSourceListener, DragSourceMotionListener, Serializable
    The DragSourceContext class is responsible for managing the initiator side of the Drag and Drop protocol. In particular, it is responsible for managing drag event notifications to the DragSourceListeners and DragSourceMotionListeners, and providing the Transferable representing the source data for the drag operation.

    Note that the DragSourceContext itself implements the DragSourceListener and DragSourceMotionListener interfaces. This is to allow the platform peer (the DragSourceContextPeer instance) created by the DragSource to notify the DragSourceContext of state changes in the ongoing operation. This allows the DragSourceContext object to interpose itself between the platform and the listeners provided by the initiator of the drag operation.

    By default, DragSourceContext sets the cursor as appropriate for the current state of the drag and drop operation. For example, if the user has chosen the move action, and the pointer is over a target that accepts the move action, the default move cursor is shown. When the pointer is over an area that does not accept the transfer, the default "no drop" cursor is shown.

    This default handling mechanism is disabled when a custom cursor is set by the setCursor(java.awt.Cursor) method. When the default handling is disabled, it becomes the responsibility of the developer to keep the cursor up to date, by listening to the DragSource events and calling the setCursor() method. Alternatively, you can provide custom cursor behavior by providing custom implementations of the DragSource and the DragSourceContext classes.

    Since:
    1.2
    See Also:
    DragSourceListener, DragSourceMotionListener, DnDConstants, Serialized Form

    • Field Summary

      Fields 
      Modifier and Type Field Description
      protected static int CHANGED
      An int used by updateCurrentCursor() indicating that the user operation has changed.
      protected static int DEFAULT
      An int used by updateCurrentCursor() indicating that the Cursor should change to the default (no drop) Cursor.
      protected static int ENTER
      An int used by updateCurrentCursor() indicating that the Cursor has entered a DropTarget.
      protected static int OVER
      An int used by updateCurrentCursor() indicating that the Cursor is over a DropTarget.

    • Constructor Summary

      Constructors 
      Constructor Description
      DragSourceContext​(DragGestureEvent trigger, Cursor dragCursor, Image dragImage, Point offset, Transferable t, DragSourceListener dsl)
      Called from DragSource, this constructor creates a new DragSourceContext given the DragSourceContextPeer for this Drag, the DragGestureEvent that triggered the Drag, the initial Cursor to use for the Drag, an (optional) Image to display while the Drag is taking place, the offset of the Image origin from the hotspot at the instant of the triggering event, the Transferable subject data, and the DragSourceListener to use during the Drag and Drop operation.

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void addDragSourceListener​(DragSourceListener dsl)
      Add a DragSourceListener to this DragSourceContext if one has not already been added.
      void dragDropEnd​(DragSourceDropEvent dsde)
      Calls dragDropEnd on the DragSourceListeners registered with this DragSourceContext and with the associated DragSource, and passes them the specified DragSourceDropEvent.
      void dragEnter​(DragSourceDragEvent dsde)
      Calls dragEnter on the DragSourceListeners registered with this DragSourceContext and with the associated DragSource, and passes them the specified DragSourceDragEvent.
      void dragExit​(DragSourceEvent dse)
      Calls dragExit on the DragSourceListeners registered with this DragSourceContext and with the associated DragSource, and passes them the specified DragSourceEvent.
      void dragMouseMoved​(DragSourceDragEvent dsde)
      Calls dragMouseMoved on the DragSourceMotionListeners registered with the DragSource associated with this DragSourceContext, and them passes the specified DragSourceDragEvent.
      void dragOver​(DragSourceDragEvent dsde)
      Calls dragOver on the DragSourceListeners registered with this DragSourceContext and with the associated DragSource, and passes them the specified DragSourceDragEvent.
      void dropActionChanged​(DragSourceDragEvent dsde)
      Calls dropActionChanged on the DragSourceListeners registered with this DragSourceContext and with the associated DragSource, and passes them the specified DragSourceDragEvent.
      Component getComponent()
      Returns the Component associated with this DragSourceContext.
      Cursor getCursor()
      Returns the current custom drag Cursor.
      DragSource getDragSource()
      Returns the DragSource that instantiated this DragSourceContext.
      int getSourceActions()
      Returns a bitwise mask of DnDConstants that represent the set of drop actions supported by the drag source for the drag operation associated with this DragSourceContext.
      Transferable getTransferable()
      Returns the Transferable associated with this DragSourceContext.
      DragGestureEvent getTrigger()
      Returns the DragGestureEvent that initially triggered the drag.
      void removeDragSourceListener​(DragSourceListener dsl)
      Removes the specified DragSourceListener from this DragSourceContext.
      void setCursor​(Cursor c)
      Sets the custom cursor for this drag operation to the specified Cursor.
      void transferablesFlavorsChanged()
      Notifies the peer that the Transferable's DataFlavors have changed.
      protected void updateCurrentCursor​(int sourceAct, int targetAct, int status)
      If the default drag cursor behavior is active, this method sets the default drag cursor for the specified actions supported by the drag source, the drop target action, and status, otherwise this method does nothing.

    • Field Detail

      • DEFAULT

        protected static final int DEFAULT
        An int used by updateCurrentCursor() indicating that the Cursor should change to the default (no drop) Cursor.
        See Also:
        Constant Field Values

      • ENTER

        protected static final int ENTER
        An int used by updateCurrentCursor() indicating that the Cursor has entered a DropTarget.
        See Also:
        Constant Field Values

      • OVER

        protected static final int OVER
        An int used by updateCurrentCursor() indicating that the Cursor is over a DropTarget.
        See Also:
        Constant Field Values

      • CHANGED

        protected static final int CHANGED
        An int used by updateCurrentCursor() indicating that the user operation has changed.
        See Also:
        Constant Field Values

    • Constructor Detail

      • DragSourceContext

        public DragSourceContext​(DragGestureEvent trigger,
                         Cursor dragCursor,
                         Image dragImage,
                         Point offset,
                         Transferable t,
                         DragSourceListener dsl)
        Called from DragSource, this constructor creates a new DragSourceContext given the DragSourceContextPeer for this Drag, the DragGestureEvent that triggered the Drag, the initial Cursor to use for the Drag, an (optional) Image to display while the Drag is taking place, the offset of the Image origin from the hotspot at the instant of the triggering event, the Transferable subject data, and the DragSourceListener to use during the Drag and Drop operation.
        If DragSourceContextPeer is null NullPointerException is thrown.
        If DragGestureEvent is null NullPointerException is thrown.
        If Cursor is null no exception is thrown and the default drag cursor behavior is activated for this drag operation.
        If Image is null no exception is thrown.
        If Image is not null and the offset is null NullPointerException is thrown.
        If Transferable is null NullPointerException is thrown.
        If DragSourceListener is null no exception is thrown.
        Parameters:
        trigger - the triggering event
        dragCursor - the initial Cursor for this drag operation or null for the default cursor handling; see class level documentation for more details on the cursor handling mechanism during drag and drop
        dragImage - the Image to drag (or null)
        offset - the offset of the image origin from the hotspot at the instant of the triggering event
        t - the Transferable
        dsl - the DragSourceListener
        Throws:
        IllegalArgumentException - if the Component associated with the trigger event is null.
        IllegalArgumentException - if the DragSource for the trigger event is null.
        IllegalArgumentException - if the drag action for the trigger event is DnDConstants.ACTION_NONE.
        IllegalArgumentException - if the source actions for the DragGestureRecognizer associated with the trigger event are equal to DnDConstants.ACTION_NONE.
        NullPointerException - if dscp, trigger, or t are null, or if dragImage is non-null and offset is null

    • Method Detail

      • getDragSource

        public DragSource getDragSource()
        Returns the DragSource that instantiated this DragSourceContext.
        Returns:
        the DragSource that instantiated this DragSourceContext

      • getComponent

        public Component getComponent()
        Returns the Component associated with this DragSourceContext.
        Returns:
        the Component that started the drag

      • getTrigger

        public DragGestureEvent getTrigger()
        Returns the DragGestureEvent that initially triggered the drag.
        Returns:
        the Event that triggered the drag

      • getSourceActions

        public int getSourceActions()
        Returns a bitwise mask of DnDConstants that represent the set of drop actions supported by the drag source for the drag operation associated with this DragSourceContext.
        Returns:
        the drop actions supported by the drag source

      • setCursor

        public void setCursor​(Cursor c)
        Sets the custom cursor for this drag operation to the specified Cursor. If the specified Cursor is null, the default drag cursor behavior is activated for this drag operation, otherwise it is deactivated.
        Parameters:
        c - the initial Cursor for this drag operation, or null for the default cursor handling; see class level documentation for more details on the cursor handling during drag and drop

      • getCursor

        public Cursor getCursor()
        Returns the current custom drag Cursor.
        Returns:
        the current custom drag Cursor, if it was set otherwise returns null.
        See Also:
        setCursor(java.awt.Cursor)

      • addDragSourceListener

        public void addDragSourceListener​(DragSourceListener dsl)
                           throws TooManyListenersException
        Add a DragSourceListener to this DragSourceContext if one has not already been added. If a DragSourceListener already exists, this method throws a TooManyListenersException.
        Parameters:
        dsl - the DragSourceListener to add. Note that while null is not prohibited, it is not acceptable as a parameter.
        Throws:
        TooManyListenersException - if a DragSourceListener has already been added

      • removeDragSourceListener

        public void removeDragSourceListener​(DragSourceListener dsl)
        Removes the specified DragSourceListener from this DragSourceContext.
        Parameters:
        dsl - the DragSourceListener to remove; note that while null is not prohibited, it is not acceptable as a parameter

      • transferablesFlavorsChanged

        public void transferablesFlavorsChanged()
        Notifies the peer that the Transferable's DataFlavors have changed.

      • dragEnter

        public void dragEnter​(DragSourceDragEvent dsde)
        Calls dragEnter on the DragSourceListeners registered with this DragSourceContext and with the associated DragSource, and passes them the specified DragSourceDragEvent.
        Specified by:
        dragEnter in interface DragSourceListener
        Parameters:
        dsde - the DragSourceDragEvent

      • dragOver

        public void dragOver​(DragSourceDragEvent dsde)
        Calls dragOver on the DragSourceListeners registered with this DragSourceContext and with the associated DragSource, and passes them the specified DragSourceDragEvent.
        Specified by:
        dragOver in interface DragSourceListener
        Parameters:
        dsde - the DragSourceDragEvent

      • dragExit

        public void dragExit​(DragSourceEvent dse)
        Calls dragExit on the DragSourceListeners registered with this DragSourceContext and with the associated DragSource, and passes them the specified DragSourceEvent.
        Specified by:
        dragExit in interface DragSourceListener
        Parameters:
        dse - the DragSourceEvent

      • dropActionChanged

        public void dropActionChanged​(DragSourceDragEvent dsde)
        Calls dropActionChanged on the DragSourceListeners registered with this DragSourceContext and with the associated DragSource, and passes them the specified DragSourceDragEvent.
        Specified by:
        dropActionChanged in interface DragSourceListener
        Parameters:
        dsde - the DragSourceDragEvent

      • dragDropEnd

        public void dragDropEnd​(DragSourceDropEvent dsde)
        Calls dragDropEnd on the DragSourceListeners registered with this DragSourceContext and with the associated DragSource, and passes them the specified DragSourceDropEvent.
        Specified by:
        dragDropEnd in interface DragSourceListener
        Parameters:
        dsde - the DragSourceDropEvent

      • dragMouseMoved

        public void dragMouseMoved​(DragSourceDragEvent dsde)
        Calls dragMouseMoved on the DragSourceMotionListeners registered with the DragSource associated with this DragSourceContext, and them passes the specified DragSourceDragEvent.
        Specified by:
        dragMouseMoved in interface DragSourceMotionListener
        Parameters:
        dsde - the DragSourceDragEvent
        Since:
        1.4

      • getTransferable

        public Transferable getTransferable()
        Returns the Transferable associated with this DragSourceContext.
        Returns:
        the Transferable

      • updateCurrentCursor

        protected void updateCurrentCursor​(int sourceAct,
                                   int targetAct,
                                   int status)
        If the default drag cursor behavior is active, this method sets the default drag cursor for the specified actions supported by the drag source, the drop target action, and status, otherwise this method does nothing.
        Parameters:
        sourceAct - the actions supported by the drag source
        targetAct - the drop target action
        status - one of the fields DEFAULT, ENTER, OVER, CHANGED