Module java.desktop
Package java.awt.dnd

Class DragSource

  • All Implemented Interfaces:
    Serializable

    public class DragSource
extends Object
implements Serializable
    The DragSource is the entity responsible for the initiation of the Drag and Drop operation, and may be used in a number of scenarios:
    • 1 default instance per JVM for the lifetime of that JVM.
    • 1 instance per class of potential Drag Initiator object (e.g TextField). [implementation dependent]
    • 1 per instance of a particular Component, or application specific object associated with a Component instance in the GUI. [implementation dependent]
    • Some other arbitrary association. [implementation dependent]
    Once the DragSource is obtained, a DragGestureRecognizer should also be obtained to associate the DragSource with a particular Component.

    The initial interpretation of the user's gesture, and the subsequent starting of the drag operation are the responsibility of the implementing Component, which is usually implemented by a DragGestureRecognizer.

    When a drag gesture occurs, the DragSource's startDrag() method shall be invoked in order to cause processing of the user's navigational gestures and delivery of Drag and Drop protocol notifications. A DragSource shall only permit a single Drag and Drop operation to be current at any one time, and shall reject any further startDrag() requests by throwing an IllegalDnDOperationException until such time as the extant operation is complete.

    The startDrag() method invokes the createDragSourceContext() method to instantiate an appropriate DragSourceContext and associate the DragSourceContextPeer with that.

    If the Drag and Drop System is unable to initiate a drag operation for some reason, the startDrag() method throws a java.awt.dnd.InvalidDnDOperationException to signal such a condition. Typically this exception is thrown when the underlying platform system is either not in a state to initiate a drag, or the parameters specified are invalid.

    Note that during the drag, the set of operations exposed by the source at the start of the drag operation may not change until the operation is complete. The operation(s) are constant for the duration of the operation with respect to the DragSource.

    Since:
    1.2
    See Also:
    Serialized Form

    • Field Detail

      • DefaultCopyDrop

        public static final Cursor DefaultCopyDrop
        The default Cursor to use with a copy operation indicating that a drop is currently allowed. null if GraphicsEnvironment.isHeadless() returns true.
        See Also:
        GraphicsEnvironment.isHeadless()

      • DefaultMoveDrop

        public static final Cursor DefaultMoveDrop
        The default Cursor to use with a move operation indicating that a drop is currently allowed. null if GraphicsEnvironment.isHeadless() returns true.
        See Also:
        GraphicsEnvironment.isHeadless()

      • DefaultLinkDrop

        public static final Cursor DefaultLinkDrop
        The default Cursor to use with a link operation indicating that a drop is currently allowed. null if GraphicsEnvironment.isHeadless() returns true.
        See Also:
        GraphicsEnvironment.isHeadless()

      • DefaultCopyNoDrop

        public static final Cursor DefaultCopyNoDrop
        The default Cursor to use with a copy operation indicating that a drop is currently not allowed. null if GraphicsEnvironment.isHeadless() returns true.
        See Also:
        GraphicsEnvironment.isHeadless()

      • DefaultMoveNoDrop

        public static final Cursor DefaultMoveNoDrop
        The default Cursor to use with a move operation indicating that a drop is currently not allowed. null if GraphicsEnvironment.isHeadless() returns true.
        See Also:
        GraphicsEnvironment.isHeadless()

      • DefaultLinkNoDrop

        public static final Cursor DefaultLinkNoDrop
        The default Cursor to use with a link operation indicating that a drop is currently not allowed. null if GraphicsEnvironment.isHeadless() returns true.
        See Also:
        GraphicsEnvironment.isHeadless()

    • Method Detail

      • getDefaultDragSource

        public static DragSource getDefaultDragSource​()
        Gets the DragSource object associated with the underlying platform.
        Returns:
        the platform DragSource
        Throws:
        HeadlessException - if GraphicsEnvironment.isHeadless() returns true
        See Also:
        GraphicsEnvironment.isHeadless()

      • isDragImageSupported

        public static boolean isDragImageSupported​()
        Reports whether or not drag Image support is available on the underlying platform.
        Returns:
        if the Drag Image support is available on this platform

      • startDrag

        public void startDrag​(DragGestureEvent trigger,
                      Cursor dragCursor,
                      Image dragImage,
                      Point imageOffset,
                      Transferable transferable,
                      DragSourceListener dsl,
                      FlavorMap flavorMap)
               throws InvalidDnDOperationException
        Start a drag, given the DragGestureEvent that initiated the drag, the initial Cursor to use, the Image to drag, the offset of the Image origin from the hotspot of the Cursor at the instant of the trigger, the Transferable subject data of the drag, the DragSourceListener, and the FlavorMap.
        Parameters:
        trigger - the DragGestureEvent that initiated the drag
        dragCursor - the initial Cursor for this drag operation or null for the default cursor handling; see DragSourceContext for more details on the cursor handling mechanism during drag and drop
        dragImage - the image to drag or null
        imageOffset - the offset of the Image origin from the hotspot of the Cursor at the instant of the trigger
        transferable - the subject data of the drag
        dsl - the DragSourceListener
        flavorMap - the FlavorMap to use, or null
        Throws:
        InvalidDnDOperationException - if the Drag and Drop system is unable to initiate a drag operation, or if the user attempts to start a drag while an existing drag operation is still executing

      • startDrag

        public void startDrag​(DragGestureEvent trigger,
                      Cursor dragCursor,
                      Transferable transferable,
                      DragSourceListener dsl,
                      FlavorMap flavorMap)
               throws InvalidDnDOperationException
        Start a drag, given the DragGestureEvent that initiated the drag, the initial Cursor to use, the Transferable subject data of the drag, the DragSourceListener, and the FlavorMap.
        Parameters:
        trigger - the DragGestureEvent that initiated the drag
        dragCursor - the initial Cursor for this drag operation or null for the default cursor handling; see DragSourceContext for more details on the cursor handling mechanism during drag and drop
        transferable - the subject data of the drag
        dsl - the DragSourceListener
        flavorMap - the FlavorMap to use or null
        Throws:
        InvalidDnDOperationException - if the Drag and Drop system is unable to initiate a drag operation, or if the user attempts to start a drag while an existing drag operation is still executing

      • startDrag

        public void startDrag​(DragGestureEvent trigger,
                      Cursor dragCursor,
                      Image dragImage,
                      Point dragOffset,
                      Transferable transferable,
                      DragSourceListener dsl)
               throws InvalidDnDOperationException
        Start a drag, given the DragGestureEvent that initiated the drag, the initial Cursor to use, the Image to drag, the offset of the Image origin from the hotspot of the Cursor at the instant of the trigger, the subject data of the drag, and the DragSourceListener.
        Parameters:
        trigger - the DragGestureEvent that initiated the drag
        dragCursor - the initial Cursor for this drag operation or null for the default cursor handling; see DragSourceContext for more details on the cursor handling mechanism during drag and drop
        dragImage - the Image to drag or null
        dragOffset - the offset of the Image origin from the hotspot of the Cursor at the instant of the trigger
        transferable - the subject data of the drag
        dsl - the DragSourceListener
        Throws:
        InvalidDnDOperationException - if the Drag and Drop system is unable to initiate a drag operation, or if the user attempts to start a drag while an existing drag operation is still executing

      • startDrag

        public void startDrag​(DragGestureEvent trigger,
                      Cursor dragCursor,
                      Transferable transferable,
                      DragSourceListener dsl)
               throws InvalidDnDOperationException
        Start a drag, given the DragGestureEvent that initiated the drag, the initial Cursor to use, the Transferable subject data of the drag, and the DragSourceListener.
        Parameters:
        trigger - the DragGestureEvent that initiated the drag
        dragCursor - the initial Cursor for this drag operation or null for the default cursor handling; see DragSourceContext class for more details on the cursor handling mechanism during drag and drop
        transferable - the subject data of the drag
        dsl - the DragSourceListener
        Throws:
        InvalidDnDOperationException - if the Drag and Drop system is unable to initiate a drag operation, or if the user attempts to start a drag while an existing drag operation is still executing

      • createDragSourceContext

        protected DragSourceContext createDragSourceContext​(DragGestureEvent dgl,
                                                    Cursor dragCursor,
                                                    Image dragImage,
                                                    Point imageOffset,
                                                    Transferable t,
                                                    DragSourceListener dsl)
        Creates the DragSourceContext to handle the current drag operation.

        To incorporate a new DragSourceContext subclass, subclass DragSource and override this method.

        If dragImage is null, no image is used to represent the drag over feedback for this drag operation, but NullPointerException is not thrown.

        If dsl is null, no drag source listener is registered with the created DragSourceContext, but NullPointerException is not thrown.

        Parameters:
        dgl - The DragGestureEvent that triggered the drag
        dragCursor - The initial Cursor for this drag operation or null for the default cursor handling; see DragSourceContext class for more details on the cursor handling mechanism during drag and drop
        dragImage - The Image to drag or null
        imageOffset - The offset of the Image origin from the hotspot of the cursor at the instant of the trigger
        t - The subject data of the drag
        dsl - The DragSourceListener
        Returns:
        the DragSourceContext
        Throws:
        NullPointerException - if dscp is null
        NullPointerException - if dgl is null
        NullPointerException - if dragImage is not null and imageOffset is null
        NullPointerException - if t is null
        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.

      • getFlavorMap

        public FlavorMap getFlavorMap​()
        This method returns the FlavorMap for this DragSource.
        Returns:
        the FlavorMap for this DragSource

      • createDragGestureRecognizer

        public <T extends DragGestureRecognizer> T createDragGestureRecognizer​(Class<T> recognizerAbstractClass,
                                                                       Component c,
                                                                       int actions,
                                                                       DragGestureListener dgl)
        Creates a new DragGestureRecognizer that implements the specified abstract subclass of DragGestureRecognizer, and sets the specified Component and DragGestureListener on the newly created object.
        Type Parameters:
        T - the type of DragGestureRecognizer to create
        Parameters:
        recognizerAbstractClass - the requested abstract type
        actions - the permitted source drag actions
        c - the Component target
        dgl - the DragGestureListener to notify
        Returns:
        the new DragGestureRecognizer or null if the Toolkit.createDragGestureRecognizer method has no implementation available for the requested DragGestureRecognizer subclass and returns null

      • createDefaultDragGestureRecognizer

        public DragGestureRecognizer createDefaultDragGestureRecognizer​(Component c,
                                                                int actions,
                                                                DragGestureListener dgl)
        Creates a new DragGestureRecognizer that implements the default abstract subclass of DragGestureRecognizer for this DragSource, and sets the specified Component and DragGestureListener on the newly created object. For this DragSource the default is MouseDragGestureRecognizer.
        Parameters:
        c - the Component target for the recognizer
        actions - the permitted source actions
        dgl - the DragGestureListener to notify
        Returns:
        the new DragGestureRecognizer or null if the Toolkit.createDragGestureRecognizer method has no implementation available for the requested DragGestureRecognizer subclass and returns null

      • removeDragSourceListener

        public void removeDragSourceListener​(DragSourceListener dsl)
        Removes the specified DragSourceListener from this DragSource. If a null listener is specified, no action is taken and no exception is thrown. If the listener specified by the argument was not previously added to this DragSource, no action is taken and no exception is thrown.
        Parameters:
        dsl - the DragSourceListener to remove
        Since:
        1.4
        See Also:
        addDragSourceListener(java.awt.dnd.DragSourceListener), getDragSourceListeners()

      • getListeners

        public <T extends EventListener> T[] getListeners​(Class<T> listenerType)
        Gets all the objects currently registered as FooListeners upon this DragSource. FooListeners are registered using the addFooListener method.
        Type Parameters:
        T - the type of listener objects
        Parameters:
        listenerType - the type of listeners requested; this parameter should specify an interface that descends from java.util.EventListener
        Returns:
        an array of all objects registered as FooListeners on this DragSource, or an empty array if no such listeners have been added
        Throws:
        ClassCastException - if listenerType doesn't specify a class or interface that implements java.util.EventListener
        Since:
        1.4
        See Also:
        getDragSourceListeners(), getDragSourceMotionListeners()

      • getDragThreshold

        public static int getDragThreshold​()
        Returns the drag gesture motion threshold. The drag gesture motion threshold defines the recommended behavior for MouseDragGestureRecognizers.

        If the system property awt.dnd.drag.threshold is set to a positive integer, this method returns the value of the system property; otherwise if a pertinent desktop property is available and supported by the implementation of the Java platform, this method returns the value of that property; otherwise this method returns some default value. The pertinent desktop property can be queried using java.awt.Toolkit.getDesktopProperty("DnD.gestureMotionThreshold").

        Returns:
        the drag gesture motion threshold
        Since:
        1.5
        See Also:
        MouseDragGestureRecognizer