C# Optional fields in application settings

Question

Is there a way to create some optional fields in application settings. For example for one client we need some client based settings in the settings file, something like this:

<?xml version="1.0"?>
<configuration>
  <configSections>
    <userSettings>
      <setting name="Client_1_out_folder" serializeAs="String">
        <value>c:\</value>
      </setting>
      <setting name="Some_other_setting" serializeAs="String">
        <value>True</value>
      </setting>
      ...

And for the other client we dont need the Client_1_out_folder at all so to keep the config file clean would be nice to remove it from the config file all together. So for client 2 that part of config file would look like:

<?xml version="1.0"?>
<configuration>
  <configSections>
    <userSettings>
      <setting name="Some_other_setting" serializeAs="String">
        <value>True</value>
      </setting>
      ...

Answer 1

Create a custon configuration section for your settings. Then on the configurationsection class, mark the property as "IsRequired=false" to make that property optional.

[ConfigurationProperty("frontPagePostCount"
    , DefaultValue = 20
    , IsRequired = false)]

Answer 2

You can create a class which inherits from ConfigurationSection.

Then, you can do practically whatever you want. It's much more powerful than the user settings.

MSDN: How to: Create Custom Configuration Sections Using ConfigurationSection

You can extend ASP.NET configuration settings with XML configuration elements of your own. To do this, you create a custom configuration section handler. The handler must be a .NET Framework class that inherits from the System.Configuration.ConfigurationSection class. The section handler interprets and processes the settings that are defined in XML configuration elements in a specific section of a Web.config file. You can read and write these settings through the handler's properties.

The article says "ASP.NET", but it's not just for ASP.NET. It works equally well for WinForms.