Eval check for DBNull doesnt work

问题

<%# Eval("Description") == DBNull.Value ? "empty" : "notempty"%>

is showing always 'notempty' even there is null in that field in DB (type of varchar(), null) ... Tried also checking for empty string:

<%# Eval("Description") == "" ? "empty" : "notempty"%>

and it always displays notempty... what's wrong here??

回答1:

There is a difference between DBNull.Value and null. It is possible the field is returning null.

Try

<%# Eval("Description") == null ? "empty" : "notempty"%>

Also if the field value type is supposed to be string you could do something along the lines of..

<%# (Eval("Description") as string) ?? "empty" %>

回答2:

Have you tried using this method:

<%# Convert.IsDBNull(Eval("Description") ? "empty" : "notempty"%>

回答3:

It is not actually storing DBNull at this level. You need to look for null or an empty string which string.IsNullOrEmpty should be enough and will capture both states of null and empty.

<%# string.IsNullOrEmpty(Eval("Description").ToString()) ? "empty" : "notempty"%>  

来源：https://stackoverflow.com/questions/5224264/eval-check-for-dbnull-doesnt-work