如何在.NET中检测运行时类的存在？

Question

是否有可能在.NET应用程序(C#)中有条件地检测是否在运行时定义了类？

示例实现 - 假设您要基于配置选项创建类对象？

Answer 1

string className="SomeClass";
Type type=Type.GetType(className);
if(type!=null)
{
//class with the given name exists
}

对于您问题的第二部分：-

示例实现 - 假设您想根据配置选项创建一个类对象？

我不知道你为什么要这样做。但是，如果您的类实现了一个接口，并且您想根据配置文件动态创建这些类的对象，我认为您可以查看Unity IoC container。如果它适合您的场景，它真的很酷并且非常易于使用。关于如何做到这一点的一个例子是here。

Answer 2

我已经做了类似的事情，从配置加载一个类并实例化它。在此示例中，我需要确保配置中指定的类继承自名为 NinjectModule 的类，但我想您已经明白了。

protected override IKernel CreateKernel()
{
    // The name of the class, e.g. retrieved from a config
    string moduleName = "MyApp.MyAppTestNinjectModule";

    // Type.GetType takes a string and tries to find a Type with
    // the *fully qualified name* - which includes the Namespace
    // and possibly also the Assembly if it's in another assembly
    Type moduleType = Type.GetType(moduleName);

    // If Type.GetType can't find the type, it returns Null
    NinjectModule module;
    if (moduleType != null)
    {
        // Activator.CreateInstance calls the parameterless constructor
        // of the given Type to create an instace. As this returns object
        // you need to cast it to the desired type, NinjectModule
        module = Activator.CreateInstance(moduleType) as NinjectModule;
    }
    else
    {
        // If the Type was not found, you need to handle that. You could instead
        // initialize Module through some default type, for example
        // module = new MyAppDefaultNinjectModule();
        // or error out - whatever suits your needs
        throw new MyAppConfigException(
             string.Format("Could not find Type: '{0}'", moduleName),
             "injectModule");
    }

    // As module is an instance of a NinjectModule (or derived) class, we
    // can use it to create Ninject's StandardKernel
    return new StandardKernel(module);
}