Question

我有两种具有多对多关系的抽象类型：

public abstract class Experiment<T> where T : Sample
{
    private List<T> _Samples = new List<T>;
    public IReadOnlyCollection<T> Samples {
        get { return _Samples.AsReadOnly(); }
    }

    public void AddSample(T sample)
    {
        _Samples.Add(sample); 
        sample.Experiments.Add(this); // The problem lies here
    }
}

public abstract class Sample
{
    private List<Experiment<Sample>> _Experiments = new List<Experiment<Sample>>;
    public ICollection<Experiment<Sample>> Experiments {
        get { return _Experiments; }
    }
}

如您所见，实验接受的类型参数是Sample的子类。我想要做的是：每当Sample的子类型的实例添加到Experiment时，Experiment应相应地添加到Experiments的{{1}}集合中Sample。

当我尝试将Experiment<T>的实例添加到List<Experiment<Sample>>的集合时，会出现问题。由于T是Sample的子类型，我假设不存在问题。实际发生的是以下内容：

Value of type 'Experiment<T>' cannot be converted to 'Experiment<Sample>`

我的问题是，是否有办法解决这个问题，或者更好地模拟这些实体之间的关系。

Answer 1

public class Experiment<T> where T : Sample
{
    private List<T> _Samples = new List<T>();
    public IReadOnlyCollection<T> Samples
    {
        get { return _Samples.AsReadOnly(); }
    }

    public Experiment()
    {
    }

    public Experiment(IEnumerable<T> samples)
    {
        _Samples = samples.ToList();
    }

    public void AddSample(T sample)
    {
        _Samples.Add(sample);
        sample.Experiments.Add(new Experiment<Sample>(_Samples)); // The problem lies here
    }
}

public abstract class Sample
{
    private List<Experiment<Sample>> _Experiments = new List<Experiment<Sample>>();
    public ICollection<Experiment<Sample>> Experiments
    {
        get { return _Experiments ; }
    }
}

通过添加一些构造函数并修改Experiments中的Sample集合，我认为我能够实现您正在寻找的东西。现在您可以使用以下代码

public class MySample : Sample{}

public class MyExperiment : Experiment<MySample>{}

MyExperiment me = new MyExperiment();
me.AddSample(new MySample());

Answer 2

所以我认为修复就是这样：

public abstract class Experiment<T> where T : Sample<T>
{
    private List<T> _Samples;
    public IReadOnlyCollection<T> Samples {
        get { return _Samples.AsReadOnly(); }
    }

    public void AddSample(T sample)
    {
        _Samples.Add(sample); 
        sample.Experiments.Add(this); // The problem lies here
    }
}

public abstract class Sample<T> where T : Sample<T>
{
    private List<Experiment<T>> _Experiments;
    public ICollection<Experiment<T>> Experiments {
        get { return _Experiments; }
    }
}

因为这两种类型相互依赖，所以它们需要共享相同的泛型类型。

为什么我不能将这个泛型类型的实例添加到集合中？

2 个答案: