Super simple WinForms config manager. TextBox saving support.

Config.cs

using System.Configuration;

public static class Config
{
    private static Configuration configManager;
    private static KeyValueConfigurationCollection configuration;

    // Support lazy loading initialization.
    private static bool hasInitialized;


    // Support manual initialization.
    public static void Initialize()
    {
        CheckInitialization();
    }

    private static void CheckInitialization()
    {
        if (!hasInitialized)
            InitializeConfig();
    }


    private static void InitializeConfig()
    {
        configManager = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
        configuration = configManager.AppSettings.Settings;
        hasInitialized = true;
    }


    public static void SaveTextBox(TextBox textBox)
    {
        CheckInitialization();
        SaveValue(textBox.Name, textBox.Text);
    }


    public static void LoadTextBox(TextBox textBox, string defaultValue)
    {
        CheckInitialization();
        string configValue = LoadValue(textBox.Name, defaultValue);
        textBox.Text = configValue;
    }


    /// <summary>
    /// Saves the given <see cref="value"/> to the config with the given <see cref="key"/>.
    /// </summary>
    public static void SaveValue(string key, string value)
    {
        CheckInitialization();

        if (TryGetConfigEntry(key, out string _))
            configuration[key].Value = value;
        else
            configuration.Add(key, value);

        configManager.Save(ConfigurationSaveMode.Modified);
        ConfigurationManager.RefreshSection(configManager.AppSettings.SectionInformation.Name);
    }


    /// <summary>
    /// Returns a value from the config with the given <see cref="key"/>.
    /// Defaults to <see cref="defaultValue"/>.
    /// </summary>
    public static string LoadValue(string key, string defaultValue = "")
    {
        CheckInitialization();

        if (TryGetConfigEntry(key, out string value)) return value;
        return defaultValue;
    }

    private static bool TryGetConfigEntry(string key, out string value)
    {
        KeyValueConfigurationElement raw = configuration[key];

        value = "";
        if (raw != null)
            value = raw.Value;

        return raw != null && raw.Value != null;
    }
}