'；的类型初始值设定项'；引发了异常

本文关键字：异常 类型 | 更新日期: 2023-09-27 18:28:16

考虑以下代码：

public class CountEnum : EnumDataType
    {
        public static readonly CountEnum CANADA = new CountEnum("CA", "Canada");
        public static readonly CountEnum DEFAULT = new CountEnum();
        private static readonly EnumDataTypeList OPTIONS = new EnumDataTypeList();
        public static readonly CountEnum UNITED_STATES = new CountEnum("US", "United States");
        public static readonly CountEnum UNSET = new CountEnum();

        private CountEnum()
        {
        }
        private CountEnum(string code, string name)
        {
            base.code = code;
            base.name = name;
            OPTIONS.Add(this); // This is the line 23
        }

以下是异常详细信息：

System.TypeInitializationException was caught
  Message=The type initializer for 'CP.BusinessLogic.VConfig' threw an exception.
  Source=CP.BusinessLogic
  TypeName=CP.BusinessLogic.VConfig
  StackTrace:
       at CP.BusinessLogic.VConfig.get_Instance()
       at CP.Fac.CPFac.GetActs() in C:'tfs_src'TeamProject'Main'Source'DApp'CPApp'Fac'CPFac.cs:line 170
  InnerException: System.TypeInitializationException
       Message=The type initializer for 'CP.Types.CountEnum' threw an exception.
       Source=CP.BusinessLogic
       TypeName=CP.Types.CountEnum
       StackTrace:
            at CP.BusinessLogic.VConfig..ctor() in C:'tfs_src'TeamProject'Main'Source'DApp'CPApp'BusinessLogic'VConfig.cs:line 14
            at CP.BusinessLogic.VConfig..cctor() in C:'tfs_src'TeamProject'Main'Source'DApp'CPApp'BusinessLogic'VConfig.cs:line 11
       InnerException: System.NullReferenceException
            Message=Object reference not set to an instance of an object.
            Source=CP.DataObject
            StackTrace:
                 at CP.Types.CountEnum..ctor(String code, String name) in C:'tfs_src'TeamProject'Main'Source'DApp'CPApp'Types'CountEnum.cs:line 23
                 at CP.Types.CountEnum..cctor() in C:'tfs_src'TeamProject'Main'Source'DApp'CPApp'Types'CountEnum.cs:line 8
            InnerException:

我无法弄清楚为什么在运行时出现此异常。我没有得到任何构建错误，代码看起来是正确的。

'；的类型初始值设定项'；引发了异常

根据堆栈跟踪判断，我认为您错过了有罪的代码。例如，也许实际上看起来是这样的：

public class CountEnum
{
   public static readonly CountEnum DEFAULT = new CountEnum();
   private static readonly List<CountEnum> AllInstances = new List<CountEnum>();
   private CountEnum()
   {
       AllInstances.Add(this);
   }
}

这将表现为堆栈跟踪显示的方式，CountEnum构造函数抛出一个NullReferenceException。然而，我们不能确定，因为您还没有包含CountEnum构造函数的主体（或者实际上根本没有发布CountEnum的有效代码）。

不过，从根本上讲，这是您应该关注的堆栈跟踪：

InnerException: System.NullReferenceException
     Message=Object reference not set to an instance of an object.
     Source=CP.DataObject
     StackTrace:
          at CP.Types.CountEnum..ctor(String code, String name) in C:'...'CountEnum.cs:line 23
          at CP.Types.CountEnum..cctor() in C:'...'CountEnum.cs:line 8

您应该查看CountEnum.cs的第23行——这就是抛出异常的原因。

编辑：好的，现在我们可以看到有问题的代码，它和我的猜测非常相似。看看这个代码：

public static readonly CountEnum CANADA = new CountEnum("CA", "Canada");
public static readonly CountEnum DEFAULT = new CountEnum();
private static readonly EnumDataTypeList OPTIONS = new EnumDataTypeList();

这些变量将按照您指定的顺序初始化，因此对CountEnum("CA", "Canada")的调用将在OPTIONS具有非null值之前执行。。。当您尝试将其添加到OPTIONS时，您将以完全正常的方式得到一个异常。

您可以通过将OPTIONS的声明移到顶部来修复此问题：

private static readonly EnumDataTypeList OPTIONS = new EnumDataTypeList();
public static readonly CountEnum CANADA = new CountEnum("CA", "Canada");
public static readonly CountEnum DEFAULT = new CountEnum();

这是可以保证的，但这是一个相当脆弱的设计。我过去曾使用过类似的设计，但当您需要特定的初始化顺序时，可能会遇到麻烦。

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