Usage "Application configuration file" is very good in creating simple applications. It's very good to store in it values like path, string for database connection or something like this. I use it for a long time. But not so long ago I have noticed that Studio highlights string where configuration file used:

[Deprecated] System.Collections.Spicialized.NameValueCollection ConfigurationSettings.AppSettings

The example of highlight is in the figure 1.

 

To fix it you should make next steps:

1. Add reference to System.Configuraion in your project (Figure 2).

2. Change "ConfigurationSettings" to "ConfigurationSettings"

 

string sourceDir = ConfigurationSettings.AppSettings["fsdir"];

to:

string sourceDir = ConfigurationManager.AppSettings["fsdir"];

 

Now no obsolete warnings about using configuration settings.