匿名方法访问局部变量时抛出运行时异常

Question

为什么下面的代码会抛出以下错误？

private static void CreateNewAppDomain() {
   var cd = AppDomain.CreateDomain("CustomDomain1");
   cd.DomainUnload += (sender, args) => Console.WriteLine("Domain 0 unloading,       sender{0}, args{1} domain {2}", sender, args,cd);
}



System.Runtime.Serialization.SerializationException was unhandled  Message=Type 'CoreConstructs.AppDomainPlay+<>c__DisplayClass3' in assembly 'CoreConstructs, Version=1.0.0.0, Culture=neutral, PublicKeyToken=2642f93804f4bbd8' is not marked as serializable.  Source=mscorlib
  StackTrace:
       at System.AppDomain.add_ProcessExit(EventHandler value)
       at CoreConstructs.AppDomainPlay.CreateNewAppDomain() in C:\work\sampleCode\exploreCsharp\exploreCSharp\ParameterPassing\AppDomainPlay.cs:line 31
       at CoreConstructs.AppDomainPlay.ExploreAppDomain() in C:\work\sampleCode\exploreCsharp\exploreCSharp\ParameterPassing\AppDomainPlay.cs:line 19
       at CoreConstructs.Program.Main(String[] args) in C:\work\sampleCode\exploreCsharp\exploreCSharp\ParameterPassing\Program.cs:line 14
       at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
       at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
  InnerException: 

Answer 1

C# 编译器生成一个不可见的帮助器类来实现 lambda。您可以在异常消息中看到它的名称<>c__DisplayClass3。由于 lambda 在添加的应用程序域中运行，因此需要将该帮助程序类的实例从主域序列化到该应用程序域。

这是行不通的，这些辅助类没有 [Serializable] 属性。此处不能使用 lambda，只需在静态辅助函数上使用常规事件分配语法即可。像这样：

       cd.DomainUnload += NewAppDomain_DomainUnload;
    ...

    private static void NewAppDomain_DomainUnload(object sender, EventArgs e) {
        Console.WriteLine("AppDomain {0} unloading", AppDomain.CurrentDomain);
    }

Answer 2

这是因为您尝试在 DomainUnload 方法内使用 cd 变量，并且该变量是在外部范围中定义的。