:itemchanged事件里面(dwo.Name)为什么报错

求助:itemchanged事件里面(dwo.Name)为什么报错?
求助:itemchanged事件里面的代码:目的是某些特定的字段改变的时候作一些事情,但是报错:代码如下

//修改招标价格后保存
string ls_col_name
ls_col_name = (dwo.Name)

If ls_col_name = 'zbsj_zbje' Or ls_col_name = 'zbsj_wxxz' Then

错误信息:NULL object reference at line 3 in itemchanged of dw_3

------解决方案--------------------
原因很简单，就是你有时候单击点中的对象或许是一条线或者是其他的对象的话 dwo.name是无效的.
itemchanged事件添加代码：
if dwo.name<>'zbsj_zbje' and dwo.name<>'zbsj_wxxz' then return
................
------解决方案--------------------
//修改招标价格后保存
if not isvalid(dwo) then return
string ls_col_name
ls_col_name = (dwo.Name)

If ls_col_name = 'zbsj_zbje' Or ls_col_name = 'zbsj_wxxz' Then
------解决方案--------------------

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//修改招标价格后保存
if not isvalid(dwo) then return
string ls_col_name
ls_col_name = (dwo.Name)

If ls_col_name = 'zbsj_zbje' Or ls_col_name = 'zbsj_wxxz' Then