using System.Configuration.Provider; namespace System.Configuration { public class SettingsProviderCollection : ProviderCollection { public new SettingsProvider this[string name] { get { return (SettingsProvider)base[name]; } } public override void Add(ProviderBase provider) { if (provider == null) throw new ArgumentNullException("provider"); if (!(provider is SettingsProvider)) throw new ArgumentException(string.Format(System.SR.Config_provider_must_implement_type, typeof(SettingsProvider).ToString()), "provider"); base.Add(provider); } } }