app.config为
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<connectionStrings>
<add
name="mainDB"
connectionString="Provider=Microsoft.Jet.OLEDB.4.0; Data Source=F:\Develop\COMMON\db.mdb"
providerName="NBear.Data.MsAccess.AccessDbProvider"
/>
</connectionStrings>
</configuration>
用System.Configuration.ConfigurationSettings.AppSettings["ConnectionString"]无法取得，原因是ConfigurationSettings过时了。
用System.Configuration.ConfigurationManager.ConnectionStrings["mainDB"].ConnectionString就ok了