抽象/虚拟方法的通用返回类型 [英] Generic return types from abstract/virtual methods

问题描述

我有两个基类之间的关系:

I have a relationship between two base classes:

public abstract class RecruiterBase<T>
{
  // Properties declare here
  // Constructors declared here

  public abstract IQueryable<T> GetCandidates();
}

public abstract class CandidateBase<T>
{
  // Properties declare here
  // Constructors declared here
}

以及它们的具体实现:

public class CandidateA : CandidateBase<CandidateA>
{
  // Constructors declared here
}

public class RecruiterA : RecruiterBase<RecruiterA>
{
  // Constructors declared here

  // ----HERE IS WHERE I AM BREAKING DOWN----
  public override IQueryable<CandidateA> GetCandidates()
  {
     return from c in db.Candidates
            where c.RecruiterId == this.RecruiterId
            select new CandidateA
            {
              CandidateId = c.CandidateId,
              CandidateName = c.CandidateName,
              RecruiterId = c.RecruiterId
            };
  }
}

根据 MSDN 文档http://msdn.microsoft.com/en-us/library/ms379564%28VS.80%29.aspx(大约一半)以及关于 SO 的类似(但不完全相同)的问题指定返回类型根据子类从基类抽象方法

Per MSDN documentation http://msdn.microsoft.com/en-us/library/ms379564%28VS.80%29.aspx (about half way down) and a similiar (but not identical) questoin on SO Specifying the return type of an abstract method from a Base Class according to a Sub Class

我可以将我的 concreate 实现用于我的重写方法 GetCandidates 的返回类型，但这不是我想要的，我想利用不同抽象类的具体实现.这是父/子数据库关系.我正在努力实现的目标是可能的吗?我目前收到一个编译时错误，我的 GetCandidates 返回类型不匹配.

I can make use of my concreate implementation for the return type of my overridden method GetCandidates but that is not what I want, I want to make use of the concrete implementation of a different abstract class. This is a parent/child database relationship. Is what I am trying to achieve possible? I currently get a compile time error that my GetCandidates return type does not match.

谢谢

推荐答案

看起来您需要定义多个泛型类型，其中一个可能被限制为从 CandidateBase 派生.

It looks like you need to define multiple generic types, with one possibly being constrained to derive from CandidateBase.

试试这样的:

public abstract class RecruiterBase<T, C> where C : CandidateBase
{
  // Properties declare here
  // Constructors declared here

  public abstract IQueryable<C> GetCandidates();
}

public abstract class CandidateBase<T>
{
  // Properties declare here
  // Constructors declared here
}

public class CandidateA : CandidateBase<CandidateA>
{
  // Constructors declared here
}

public class RecruiterA : RecruiterBase<RecruiterA, CandidateA>
{
  public override IQueryable<CandidateA> GetCandidates()
  {
     return from c in db.Candidates
            where c.RecruiterId == this.RecruiterId
            select new CandidateA
            {
              CandidateId = c.CandidateId,
              CandidateName = c.CandidateName,
              RecruiterId = c.RecruiterId
            };
  }
}

编辑包括克里斯的更正

这篇关于抽象/虚拟方法的通用返回类型的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！