Question

好的，这让我感到困惑。我有一个名为Testbase的抽象基类，它有一个名为RunTest的抽象函数。在一个文件夹中，我有一组继承此抽象类的类。在测试控制器中，我调用以下代码来创建这些测试类的实例列表。

        String ns = "HCTCommon.Tests";
        var query = from t in Assembly.GetExecutingAssembly().GetTypes()
                    where t.Namespace == ns
                    select t;

        foreach (object t in query)
        {
            TestBase test = (TestBase)Activator.CreateInstance(t as Type);
            testList.Add(test);
        }

在其中一个类RunTest函数中我正在清理代码并决定使用lambda表达式并尝试了各种版本。

pullservice = ServiceController.GetServices().FirstOrDefault(s => s.ServiceName == serviceName);

和

pullservice = ServiceController.GetServices().Where(s => s.DisplayName.Equals("Pull Service")).ToList()[0];

是我记得的那些但是无论何时我使用lambda而不是通过一些复杂的foreach循环我在代码行上得到一个invalidcastexception

TestBase test = (TestBase)Activator.CreateInstance(t as Type);

例外：

Unable to cast object of type '<>c__DisplayClass4' to type 'HCTCommon.TestBase'.

Stack Trace:

   at HCTCommon.TestController.populateTestList()
   at HCTCommon.TestController..ctor(RegistryKey Key)
   at HealthCheck.HealthCheckForm.InitializeTestPanels() in C:\Users\bkoch.ESI911\documents\visual studio 2010\Projects\HCTCommon\HealthCheck\HealthCheckForm.cs:line 55
   at HealthCheck.HealthCheckForm..ctor() in C:\Users\bkoch.ESI911\documents\visual studio 2010\Projects\HCTCommon\HealthCheck\HealthCheckForm.cs:line 26
   at HealthCheck.Program.registrycheck() in C:\Users\bkoch.ESI911\documents\visual studio 2010\Projects\HCTCommon\HealthCheck\Program.cs:line 63
   at HealthCheck.Program.Main() in C:\Users\bkoch.ESI911\documents\visual studio 2010\Projects\HCTCommon\HealthCheck\Program.cs:line 34
   at System.AppDomain._nExecuteAssembly(Assembly 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)
   at System.Threading.ThreadHelper.ThreadStart()

Answer 1

lambda表达式生成一个匿名闭包类来保存局部变量您的代码错误地选择了此类。

你应该添加

where typeof(TestBase).IsAssignableFrom(t)

Answer 2

您需要检查类型是否实际延伸Testbase：

var testList = (from t in Assembly.GetExecutingAssembly().GetTypes()
                where t.Namespace == ns && typeof(TestBase).IsAssignableFrom(t)
                select (TestBase)Activator.CreateInstance(t)
               ).ToList();

使用Lambda表达式会导致更改类类型

2 个答案: