直接SQL报表中，如何取到报表中的值？

this.Model.GetValue(e.ColKey,e.Rowi).tostring();取到的值是null

using Kingdee.BOS.Contracts;
using Kingdee.BOS.Orm.DataEntity;
using Kingdee.BOS.App;
using Kingdee.BOS;
using Kingdee.BOS.ServiceHelper;
using Kingdee.BOS.Core.DynamicForm.PlugIn.Args;
using Kingdee.BOS.Core.Bill;
using Kingdee.BOS.Core.Bill.PlugIn;
using Kingdee.BOS.Core.Metadata.EntityElement;
using Kingdee.BOS.Core.DynamicForm.PlugIn;

namespace ZC.LT.ltcb
{
[Description("lt_test_bb")]
public class lt_test_bb : AbstractDynamicFormPlugIn
{

public override void EntityRowDoubleClick(EntityRowClickEventArgs e)
{
base.EntityRowDoubleClick(e);
string tt=this.Model.GetValue("", 0).ToString();
}