读取自定义配置部分时出错：没有为此对象定义无参数构造函数

Question

从 web.config 中读取自定义配置部分非常痛苦： 我正在使用配置部分设计器 (http://csd.codeplex.com/)。

更新：

这是我得到的错误：

System.Configuration.ConfigurationErrorsException：为 SendToTestConfig/sendToTestIndexConfig 创建配置节处理程序时出错：没有为此对象定义无参数构造函数。 （C:\TFS\Mainline\Business.Utility.SendToTest\Business.Utility.SendToTest\web.config 第 20 行）---> System.MissingMethodException：没有为此对象定义无参数构造函数。 在 System.RuntimeTypeHandle.CreateInstance（RuntimeType 类型，Boolean publicOnly，Boolean noCheck，Boolean& canBeCached，RuntimeMethodHandle& ctor，Boolean& bNeedSecurityCheck） 在 System.RuntimeType.CreateInstanceSlow（布尔 publicOnly，布尔填充缓存） 在 System.RuntimeType.CreateInstanceImpl(Boolean publicOnly, Boolean skipVisibilityChecks, Boolean fillCache)

这是我自动生成的配置部分：

//------------------------------------------------------------------------------
// <auto-generated>
//     This code was generated by a tool.
//     Runtime Version:4.0.30319.225
//
//     Changes to this file may cause incorrect behavior and will be lost if
//     the code is regenerated.
// </auto-generated>
//------------------------------------------------------------------------------

namespace Business.Utility.SendToTest.Configuration
{


    /// <summary>
    /// The SendToTestIndexConfig Configuration Section.
    /// </summary>
    public partial class SendToTestIndexConfig : global::System.Configuration.ConfigurationSection
    {


        #region Singleton Instance
        /// <summary>
        /// The XML name of the SendToTestIndexConfig Configuration Section.
        /// </summary>
        [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ConfigurationSectionDesigner.CsdFileGenerator", "2.0.0.0")]
        internal const string SendToTestIndexConfigSectionName = "sendToTestIndexConfig";

        /// <summary>
        /// Gets the SendToTestIndexConfig instance.
        /// </summary>
        [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ConfigurationSectionDesigner.CsdFileGenerator", "2.0.0.0")]
        public static global::Business.Utility.SendToTest.Configuration.SendToTestIndexConfig Instance
        {
            get
            {
                return ((global::Business.Utility.SendToTest.Configuration.SendToTestIndexConfig)(global::System.Configuration.ConfigurationManager.GetSection(global::Business.Utility.SendToTest.Configuration.SendToTestIndexConfig.SendToTestIndexConfigSectionName)));
            }
        }
        #endregion

        #region Xmlns Property
        /// <summary>
        /// The XML name of the <see cref="Xmlns"/> property.
        /// </summary>
        [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ConfigurationSectionDesigner.CsdFileGenerator", "2.0.0.0")]
        internal const string XmlnsPropertyName = "xmlns";

        /// <summary>
        /// Gets the XML namespace of this Configuration Section.
        /// </summary>
        /// <remarks>
        /// This property makes sure that if the configuration file contains the XML namespace,
        /// the parser doesn't throw an exception because it encounters the unknown "xmlns" attribute.
        /// </remarks>
        [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ConfigurationSectionDesigner.CsdFileGenerator", "2.0.0.0")]
        [global::System.Configuration.ConfigurationPropertyAttribute(global::Business.Utility.SendToTest.Configuration.SendToTestIndexConfig.XmlnsPropertyName, IsRequired=false, IsKey=false, IsDefaultCollection=false)]
        public string Xmlns
        {
            get
            {
                return ((string)(base[global::Business.Utility.SendToTest.Configuration.SendToTestIndexConfig.XmlnsPropertyName]));
            }
        }
        #endregion

        #region IsReadOnly override
        /// <summary>
        /// Gets a value indicating whether the element is read-only.
        /// </summary>
        [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ConfigurationSectionDesigner.CsdFileGenerator", "2.0.0.0")]
        public override bool IsReadOnly()
        {
            return false;
        }
        #endregion

        #region appGroups Property
        /// <summary>
        /// The XML name of the <see cref="appGroups"/> property.
        /// </summary>
        [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ConfigurationSectionDesigner.CsdFileGenerator", "2.0.0.0")]
        internal const string appGroupsPropertyName = "appGroups";

        /// <summary>
        /// Gets or sets the appGroups.
        /// </summary>
        [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ConfigurationSectionDesigner.CsdFileGenerator", "2.0.0.0")]
        [global::System.ComponentModel.DescriptionAttribute("The appGroups.")]
        [global::System.Configuration.ConfigurationPropertyAttribute(global::Business.Utility.SendToTest.Configuration.SendToTestIndexConfig.appGroupsPropertyName, IsRequired=true, IsKey=false, IsDefaultCollection=false)]
        public global::Business.Utility.SendToTest.Configuration.AppGroupSettingsCollection appGroups
        {
            get
            {
                return ((global::Business.Utility.SendToTest.Configuration.AppGroupSettingsCollection)(base[global::Business.Utility.SendToTest.Configuration.SendToTestIndexConfig.appGroupsPropertyName]));
            }
            set
            {
                base[global::Business.Utility.SendToTest.Configuration.SendToTestIndexConfig.appGroupsPropertyName] = value;
            }
        }
        #endregion
    }
}
namespace Business.Utility.SendToTest.Configuration
{
   ... 

这是我的配置文件：

<?xml version="1.0"?>
<configuration>
  <configSections>
    <sectionGroup name="SendToTestConfig" type="System.Configuration.ConfigurationSectionGroup, System.Configuration, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a">
      <section name="sendToTestIndexConfig" type="Business.Utility.SendToTest.Configuration.SendToTestIndexConfig, Business.Utility.SendToTest.Configuration"/>
    </sectionGroup>
etc.

  </configSections>
    <SendToTestConfig xmlns="Business.Utility.SendToTest.Configuration">
      <sendToTestIndexConfig>
        <appGroups>
          <!-- TODO Change indexFileNamePrefix to desired value-->
          <appGroupSettings name="ItemBased" indexFileNamePrefix="S" indexFolderLocation="C:\TFS\Mainline\Business.Utility.SendToTest\Business.Utility.SendToTest" imageFolderLocation="C:\TFS\Mainline\Business.Utility.SendToTest\Business.Utility.SendToTest">
            <topicEntries>
              <topicEntry topicIDSuffix="DATE" addDuplicateVSAMEntry="true">
                <itemSubFields>
                  <subField index="0" typeName="Date"/>
                </itemSubFields>
              </topicEntry>
              <topicEntry topicIDSuffix="Item" addDuplicateVSAMEntry="true">
                <itemSubFields>
                  <subField index="0" typeName="ItemNumber"/>
                </itemSubFields>
              </topicEntry>
              <topicEntry topicIDSuffix="DESCR">
                <itemSubFields>
                  <subField index="0" typeName="LongDescription"/>
                </itemSubFields>
              </topicEntry>
            </topicEntries>
          </appGroupSettings>
      </appGroups>
    </sendToTestIndexConfig>
  </SendToTestConfig>
...
</configuration>

我已经尝试了以下所有方法，但前几个 config（我认为这是有道理的）我一直得到 null，其余的都得到上述异常。

//These return null:
SendToTestIndexConfig config = SendToTestIndexConfig.Instance;
//SendToTestIndexConfig config = (SendToTestIndexConfig) ConfigurationManager.GetSection("sendToTestIndexConfig");
//SendToTestIndexConfig configb = (SendToTestIndexConfig)WebConfigurationManager.GetSection("sendToTestIndexConfig");
//SendToTestIndexConfig configc = (SendToTestIndexConfig)WebConfigurationManager.OpenWebConfiguration(null).GetSection("sendToTestIndexConfig");
//SendToTestIndexConfig configd = (SendToTestIndexConfig)WebConfigurationManager.GetWebApplicationSection("sendToTestIndexConfig");
//SendToTestIndexConfig configf = (SendToTestIndexConfig)WebConfigurationManager.GetSection("sendToTestIndexConfig");


////These throw a "parameterless constructor error" on object "SendToTestConfig/sendToTestIndexConfig"
//SendToTestIndexConfig configg = (SendToTestIndexConfig)WebConfigurationManager.GetSection("SendToTestConfig/sendToTestIndexConfig");
//SendToTestIndexConfig configh = (SendToTestIndexConfig)WebConfigurationManager.OpenWebConfiguration(null).GetSection("SendToTestConfig/sendToTestIndexConfig");
//SendToTestIndexConfig configi = (SendToTestIndexConfig)WebConfigurationManager.GetWebApplicationSection("SendToTestConfig/sendToTestIndexConfig");
//SendToTestIndexConfig configj = (SendToTestIndexConfig)WebConfigurationManager.GetSection("SendToTestConfig/sendToTestIndexConfig");

我猜这与我的命名有关。 ConfigurationManager.AppSettings 工作正常，所以我知道我有正确的 web.config。

Answer 1

实际上，在MSDN 上的GenericEnumConverter 示例中简洁地说明了问题的解决方案。我做了你可能做过的同样的事情，并在我的配置部分属性之一上明确设置了 [TypeConverter(typeof(GenericEnumConverter))] 属性并得到了同样的错误。根据上面链接的GenericEnumConverter 的文档，您无需设置此属性即可使用GenericEnumConverter 类型转换器——它由框架隐式调用。从您的配置属性规范中删除该属性，此错误应该会消失，一切都应该正常工作。

以下是使用Enum 的配置节属性示例：

    public enum UsernameFormat
    {
        DownLevelDomainName,
        UsernameOnly,
        UserPrincipalName
    }

    public class WindowsADElement : ConfigurationElement
    {
        // This property will implicitly use the GenericEnumConverter type converter.
        [ConfigurationProperty("usernameFormat", IsRequired=true, DefaultValue=UsernameFormat.UserPrincipalName)]
        public UsernameFormat UsernameFormat
        {
            get { return (UsernameFormat)this["usernameFormat"]; }
            set { this["usernameFormat"] = value; }
    }

然后，在代码中使用它：

    MyConfigurationSection config = ConfigurationManager.GetSection("myConfigurationSection") as MyConfigurationSection;
    UsernameFormat format = config.UsernameLookup.WindowsAD.UsernameFormat;

希望对您有所帮助。

Answer 2

我不确定这是否是最佳解决方案，但我能够解决这个问题。错误是因为我使用GenericEnumTypeConverter 类将配置字符串转换为AppGroup 和SubFieldTypes 枚举。我创建了自己的自定义 TypeConverters，它解决了这个问题。显然，GenericEnumTypeConverter 没有无参数构造函数，需要构造函数的枚举类型。很想知道是否有办法使用GenericEnumTypeConverter，但这对我有用。

这让我知道了答案：Configuration Error With Custom Behaviour