Flex DataGridColumn number sort function

private function numberSortCompareFunction(field:String):Function
			{	
				return function (obj1:Object, obj2:Object):int {
					var value1:Number = (obj1[field] == "" || obj1[field] == null) ? null : new Number(obj1[field]);
					var value2:Number = (obj2[field] == "" || obj2[field]== null) ? null : new Number(obj2[field]);
					if (value1 < value2)
					{
						return -1;
					}
					else if (value1 > value2)
					{
						return 1;
					}
					else
					{
						return 0;
					}
				}
			} 

    按数字排序，这个方法可以通用与多个DataGridColumn， 不必因为dataField的不同而重新写function