You say
The error is on
string constr=ConfigurationManager.ConnectionStrings["ConString"].ConnectionString;
Have you checked that your
ConfigurationManager.ConnectionStrings
has a value for
Constring
?
Incidentally, in your reply to @OriginalGriff you have
string constr = ConfigurationManager.ConnectionStrings["Constring"]!=null?ConfigurationManager.ConnectionStrings["Constring"].ConnectionString:null;
which can be simplified to
string constr = ConfigurationManager.ConnectionStrings["Constring"]?.ConnectionString;
but string is not nullable so you should have
string constr = ConfigurationManager.ConnectionStrings["Constring"] == null ? "" : ConfigurationManager.ConnectionStrings["Constring"].ConnectionString;