C#更新对象值//删除时异常 Object reference not set to an instance of an object.

更新实体时，查询结果后用qcmbatch.BatchId的形式更改要更新的属性值（而不是new新实体【qcmbatch = new QcmBatch() 】x）

if (InTag.final_decision=="部分合格"){qcmbatch = ctx.Qcmbatch.Where(t => pareTo(sBatchId) == 0 && t.Factory == sFactory).FirstOrDefault();qcmbatch.BatchId = sBatchId;qcmbatch.BatchStatus = "已判定";qcmbatch.FinalDecision = sFinalDecision;qcmbatch.TotQty2 = sQtyPass;qcmbatch.TotQty3 = sQtyFail;qcmbatch.UpdateTime = DBGV._dbc.DB_GetSysTime();qcmbatch.UpdateUserId = InTag._cmn_in._user_id;ctx.Qcmbatch.Update(qcmbatch);}

另：

1、当主键也能更改时，需先将查出的实体数据删除，再Insert；

2、获取下拉列表的选中的值（是Text而不是SelectIndex）；

================================================

Object reference not set to an instance of an object.

执行过程中遇到空对象，逐步调试，找出null对象再对症下药。