一个关于drag and drop出错的问题

拖的时候出现了以下的错误？怎么回事？

Exception in thread "AWT-EventQueue-0" java.awt.dnd.InvalidDnDOperationException: Drag and drop in progress

at sun.awt.dnd.SunDragSourceContextPeer.setDragDropInProgress(SunDragSourceContextPeer.java:298)

at java.awt.dnd.DragSource.startDrag(DragSource.java:286)

at java.awt.dnd.DragSource.startDrag(DragSource.java:403)

at java.awt.dnd.DragGestureEvent.startDrag(DragGestureEvent.java:223)

at client.essp.treetotree.TreeDragSource$1.dragGestureRecognized(TreeDragSource.java:65)

at java.awt.dnd.DragGestureRecognizer.fireDragGestureRecognized(DragGestureRecognizer.java:339)

at sun.awt.windows.WMouseDragGestureRecognizer.mouseDragged(WMouseDragGestureRecognizer.java:202)

at java.awt.AWTEventMulticaster.mouseDragged(AWTEventMulticaster.java:262)

at java.awt.AWTEventMulticaster.mouseDragged(AWTEventMulticaster.java:261)

at java.awt.Component.processMouseMotionEvent(Component.java:5536)

at javax.swing.JComponent.processMouseMotionEvent(JComponent.java:3144)

at java.awt.Component.processEvent(Component.java:5257)

at java.awt.Container.processEvent(Container.java:1966)

at java.awt.Component.dispatchEventImpl(Component.java:3955)

at java.awt.Container.dispatchEventImpl(Container.java:2024)

at java.awt.Component.dispatchEvent(Component.java:3803)

at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4212)

at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3909)

at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3822)

at java.awt.Container.dispatchEventImpl(Container.java:2010)

at java.awt.Window.dispatchEventImpl(Window.java:1774)

at java.awt.Component.dispatchEvent(Component.java:3803)

at java.awt.EventQueue.dispatchEvent(EventQueue.java:463)

at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:242)

at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:163)

at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:157)

at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:149)

at java.awt.EventDispatchThread.run(EventDispatchThread.java:110)

程序段：

public DragSource create() {
DragSource dragSource = DragSource.getDefaultDragSource();
final String draggedValue=null;

dragSource.createDefaultDragGestureRecognizer(
treeTable.getTreeTable(),
DnDConstants.ACTION_COPY_OR_MOVE,
new DragGestureListener() {
public void dragGestureRecognized(DragGestureEvent event) {
DtoTreeNode dto = (DtoTreeNode) treeTable.getTreeTable().getSelectedNode();
if( dto == null ){
return;
}

String draggedValue=((DtoTree) dto.getDataBean()).getName();
Transferable transferable = new TreeTransferable(dto);
event.startDrag(null, transferable, new TreeDragSourceListener(draggedValue));//提示的出错点
}
});

return dragSource;
}

自己已经解决了，嘿嘿！！