使用Linq按具体类型获取IList项目

Question

So I have the following:

public IList<ISignupStepViewModel> Steps { get; set; }

An example of a concrete implementations of ISignupStepViewModel would be:

public class SignupStepBillingViewModel : ISignupStepViewModel
 public class SignupStepPricingViewModel : ISignupStepViewModel

I initialize Steps with concrete classes that implement ISignupStepViewModel with the following:

Steps = typeof (ISignupStepViewModel)
            .Assembly
            .GetTypes()
            .Where(t => !t.IsAbstract && typeof (ISignupStepViewModel).IsAssignableFrom(t))
            .Select(t => (ISignupStepViewModel) Activator.CreateInstance(t))
            .ToList();

I would like to now get a specific item in IList<ISignupStepViewModel> Steps with Linq, something like:

var billingStep = (SignupStepBillingViewModel)signupObj.Steps.FirstOrDefault(t => typeof(t) == SignupStepBillingViewModel);

Is there a way to do this? Currently I am getting the error "Class name is not valid at this point" on SignupStepBillingViewModel in bold:

(SignupStepBillingViewModel)signupObj.Steps.FirstOrDefault(t => typeof(t) == SignupStepBillingViewModel );

Answer 1

尝试使用关键字： is代替： typeof（t）== SignupStepBillingViewModel

var billingSteps = signupObj.Steps.Where(t => t is SignupStepBillingViewModel).Select(t => (SignupStepBillingViewModel)t).ToList();

Answer 2

尝试这个：

signupObj.Steps.FirstOrDefault(t => t.GetType() == typeof(SignupStepPricingViewModel)) as SignupStepPricingViewModel;

Answer 3

感谢@JonSkeet在评论中建议的所有帮助和最简单的解决方案是：

 var billingStep = Steps.OfType<SignupStepBillingViewModel>().First();

Answer 4

This code

Steps.Select(t => typeof(t) == SignupStepBillingViewModel);

will produce a collection of bool values which you then try to case to your object. Try this:

var billingStep = (SignupStepBillingViewModel)Steps.FirstOrDefault(t => typeof(t) == SignupStepBillingViewModel);