控件下的Lookup方法

如果想重写系统的某个数据源下的字段的Lookup，则可以在此控件下重写Lookup方法，不调用其父级数据源下字段的looku即可。

以下是一个关于重写Lookup方法的例子，可参考：

 [FormControlEventHandler(formControlStr(SalesTable, SalesLine_ItemId), FormControlEventType::Lookup)]
    public static void SalesLine_ItemId_OnLookup(FormControl sender, FormControlEventArgs e)
    {
        query                   query ;
        QueryBuildDataSource    qbds;
        container               con;
        SalesTable              salesTable;
        SalesLine               salesline,origSalesLine;
        FormStringControl       stringControlItemId;
        FormRun                 element         = sender.formRun();
        FormObjectSet           dateSource      = element.dataSource();
        sysTableLookup          sysTableLookup  = SysTableLookup::newParameters(tableNum(InventTable), sender);

        salesline   = dateSource.cursor();
        salesTable  = salesline.salesTable();
        
        query       = new query();
        qbds        = query.addDataSource(tableNum(InventTable));

        //如果有原订单存在，则新建物料时过滤下拉
        if(salesTable.OrigSalesId && SalesTable::checkExist(salesTable.OrigSalesId))
        {

            while select ItemId from origSalesLine
                where origSalesLine.SalesId == salesTable.OrigSalesId
            {
                con += origSalesLine.ItemId;
            }

            qbds.addRange(fieldnum(InventTable,ItemId)).value(con2Str(con));
        }
        
        sysTableLookup.parmQuery(query);
   
        sysTableLookup.addLookupfield(fieldNum(InventTable,ItemId));//下拉显示的字段
        sysTableLookup.performFormLookup();

        FormControlCancelableSuperEventArgs ce = e as FormControlCancelableSuperEventArgs;
        ce.CancelSuperCall();//不调用其父类的Lookup，数据源中的Lookup。
    }