public static string GetAppSettingsValue(string key)
{
    ConfigurationManager.RefreshSection("appSettings");
    return ConfigurationManager.AppSettings[key] ?? string.Empty;
}
public static bool UpdateAppSettings(string key, string value)
{
    var _config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
    if (!_config.HasFile)
    {
 throw new ArgumentException("程序配置文件缺失！");
    }
    KeyValueConfigurationElement _key = _config.AppSettings.Settings[key];
    if (_key == null)
 _config.AppSettings.Settings.Add(key, value);
    else
 _config.AppSettings.Settings[key].Value = value;
    _config.Save(ConfigurationSaveMode.Modified);
    return true;
}