Question

I have an app.config file that looks like this:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <appSettings>
    <add key="TestKey" value="TestValue" />
  </appSettings>
  <newSection>
  </newSection>
</configuration>

And I’m trying to use it in this way:

System.Configuration.ConfigurationFileMap fileMap = new ConfigurationFileMap(@"C:\app.config");  
System.Configuration.Configuration configuration = System.Configuration.ConfigurationManager.OpenMappedMachineConfiguration(fileMap); 

However, it doesn’t seem to be working. When I break and debug right after the file is read in, and I try to look at configuration.AppSettings I get an 'configuration.AppSettings' threw an exception of type 'System.InvalidCastException'.

I’m sure I’m reading the file, because when I look at configuration.Sections[“newSection”] I am returned an empty {System.Configuration.DefaultSection} (rather than null).

I’m guessing I’ve got something very basic wrong…what’s going on with AppSettings?

Answer 1

You are using a wrong function to read the app.config. OpenMappedMachineConfiguration is intended to open your machine.config file, but you are opening a typical application.exe.config file.
The following code will read your app.config and return what you’d expect.

    System.Configuration.ExeConfigurationFileMap fileMap = new ExeConfigurationFileMap();
    fileMap.ExeConfigFilename = @"C:\app.config";
    System.Configuration.Configuration configuration = System.Configuration.ConfigurationManager.OpenMappedExeConfiguration(fileMap, ConfigurationUserLevel.None);
    MessageBox.Show(configuration.AppSettings.Settings["TestKey"].Value);