请问怎样实现多个grid之间的数据互相拖拽？

ext官方给的例子，只支持两个grid之间的数据互相拖拽，我想实现多个grid间的数据互相拖拽，请问高手怎么实现？

[code="java"]

/*!

• Ext JS Library 3.3.0
• Copyright(c) 2006-2010 Ext JS, Inc.
• licensing@extjs.com

• http://www.extjs.com/license
  */
  Ext.onReady(function(){

  var myData = {
  records : [
  { name : "Rec 0", column1 : "0", column2 : "0" },
  { name : "Rec 1", column1 : "1", column2 : "1" },
  { name : "Rec 2", column1 : "2", column2 : "2" },
  { name : "Rec 3", column1 : "3", column2 : "3" },
  { name : "Rec 4", column1 : "4", column2 : "4" },
  { name : "Rec 5", column1 : "5", column2 : "5" },
  { name : "Rec 6", column1 : "6", column2 : "6" },
  { name : "Rec 7", column1 : "7", column2 : "7" },
  { name : "Rec 8", column1 : "8", column2 : "8" },
  { name : "Rec 9", column1 : "9", column2 : "9" }
  ]
  };

  // Generic fields array to use in both store defs.
  var fields = [
  {name: 'name', mapping : 'name'},
  {name: 'column1', mapping : 'column1'},
  {name: 'column2', mapping : 'column2'}
  ];

  // create the data store
  var firstGridStore = new Ext.data.JsonStore({
  fields : fields,
  data : myData,
  root : 'records'
  });

  // Column Model shortcut array
  var cols = [
  { id : 'name', header: "Record Name", width: 160, sortable: true, dataIndex: 'name'},
  {header: "column1", width: 50, sortable: true, dataIndex: 'column1'},
  {header: "column2", width: 50, sortable: true, dataIndex: 'column2'}
  ];

  // declare the source Grid
  var firstGrid = new Ext.grid.GridPanel({
  ddGroup : 'gridDDGroup',
  store : firstGridStore,
  columns : cols,
  enableDragDrop : true,
  stripeRows : true,
  autoExpandColumn : 'name',
  title : 'First Grid'
  });

  var secondGridStore = new Ext.data.JsonStore({
  fields : fields,
  root : 'records'
  });

  // create the destination Grid
  var secondGrid = new Ext.grid.GridPanel({
  ddGroup : 'gridDDGroup',
  store : secondGridStore,
  columns : cols,
  enableDragDrop : true,
  stripeRows : true,
  autoExpandColumn : 'name',
  title : 'Second Grid'
  });

  var store3 = new Ext.data.JsonStore({
  fields : fields,
  root : 'records'
  });

  // create the destination Grid
  var grid3 = new Ext.grid.GridPanel({
  ddGroup : 'gridDDGroup',
  store : store3,
  columns : cols,
  enableDragDrop : true,
  stripeRows : true,
  autoExpandColumn : 'name',
  title : 'Second Grid'
  });

  //Simple 'border layout' panel to house both grids
  var displayPanel = new Ext.Panel({
  width : 650,
  height : 300,
  layout : 'hbox',
  renderTo : 'panel',
  defaults : { flex : 1 }, //auto stretch
  layoutConfig : { align : 'stretch' },
  items : [
  firstGrid,
  secondGrid,
  grid3
  ],
  bbar : [
  '->', // Fill
  {
  text : 'Reset both grids',
  handler : function() {
  //refresh source grid
  firstGridStore.loadData(myData);

              //purge destination grid
              secondGridStore.removeAll();
          }
      }
  ]
  

  });

  // used to add records to the destination stores
  var blankRecord = Ext.data.Record.create(fields);

  /****
  * Setup Drop Targets
  ***/
  // This will make sure we only drop to the  view scroller element
  var firstGridDropTargetEl =  firstGrid.getView().scroller.dom;
  var firstGridDropTarget = new Ext.dd.DropTarget(firstGridDropTargetEl, {
          ddGroup    : 'gridDDGroup',
          notifyDrop : function(ddSource, e, data){
                  var records =  ddSource.dragData.selections;
                  Ext.each(records, ddSource.grid.store.remove, ddSource.grid.store);
                  firstGrid.store.add(records);
                  firstGrid.store.sort('name', 'ASC');
                  return true
          }
  });
  
  // This will make sure we only drop to the view scroller element
  var secondGridDropTargetEl = secondGrid.getView().scroller.dom;
  var secondGridDropTarget = new Ext.dd.DropTarget(secondGridDropTargetEl, {
          ddGroup    : 'gridDDGroup',
          notifyDrop : function(ddSource, e, data){
                  var records =  ddSource.dragData.selections;
                  Ext.each(records, ddSource.grid.store.remove, ddSource.grid.store);
                  secondGrid.store.add(records);
                  secondGrid.store.sort('name', 'ASC');
                  return true
          }
  });
  
  var gridDropTargetEl3 = grid3.getView().scroller.dom;
  var gridDropTarget3 = new Ext.dd.DropTarget(gridDropTargetEl3, {
          ddGroup    : 'gridDDGroup',
          notifyDrop : function(ddSource, e, data){
                  var records =  ddSource.dragData.selections;
                  Ext.each(records, ddSource.grid.store.remove, ddSource.grid.store);
                  grid3.store.add(records);
                  grid3.store.sort('name', 'ASC');
                  return true
          }
  });
  

  });

[/code]