我是新来的桌面应用程序的开发和目前正在建设使用分层架构（用户界面，DAL，BLL）的桌面应用程序。

I am new to desktop application development and currently building a desktop application using layered architecture (user interface, DAL, BLL).

在web开发我用来存放在web.config中的连接字符串和我的类库是从那里访​​问它。请指导我如何和放大器;其中，连接字符串应存放于DAL在桌面应用程序。我想在我的课库中添加的app.config 文件和访问这样的连接字符串：

In web development I used to store the connection string in web.config and my class library was accessing it from there. Please guide me how & where connection string should be stored for DAL in desktop application. I tried to add an app.config file in my class library and access the connection string like this:

ConfigurationManager.ConnectionStrings["connectionstring"].ConnectionString)

但throuws错误：。未将对象引用设置到对象的实例的

请指导我在此。感谢您的支持和分享。

Kindly guide me on this. Thanks for your support and sharing.

推荐答案

是的，在一个桌面应用程序，所有的配置应该在的app.config 该应用程序。使用该桌面应用程序将得到他们的配置从的app.config 默认的类库。

Yes, in a desktop application, all configuration should be in the app.config for that application. The class libraries used by this desktop application will get their config from that app.config by default.

如果该行抛出一个异常：

If this line throws an exception:

ConfigurationManager.ConnectionStrings["connectionstring"].ConnectionString

那么它极有可能是因为没有＆LT;的ConnectionStrings＆GT; 的名称输入ConnectionString的存在。检查空：

then it's most likely because no <connectionStrings> entry of name "connectionstring" exists. Check for NULL:

if(ConfigurationManager.ConnectionStrings["connectionstring"] != null)
{
    string connStr = ConfigurationManager.ConnectionStrings["connectionstring"].ConnectionString;
 }