Question

我需要一个返回keySelector的方法，该方法可以在调用OrderBy表达式时使用。问题是keySelector是泛型委托，我希望该方法在TKey上返回具有不同数据类型的keySelector：

Func<TSource,TKey> keySelector

我想完成此操作，但不是使用lambda表达式，而是一种返回keySelector（TKey = string或int）的方法：

IEnumerable<Person> orderedByFirstName = persons.OrderBy(p => p.FirstName);
IEnumerable<Person> orderedByAge = persons.OrderBy(p => p.Age);

是否可以通过某种方式在TKey上返回具有不同类型的keySelector的方法？不可能返回lambda表达式，但是类似的东西...

只要该方法仅返回数据类型为string的keySelector，一切正常：

public class Person
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public int Age { get; set; }
}

public class Behavior
{
    public virtual string GetOrderByKeySelector(Person p)
    {
        return p.FirstName;
    }
}

public class SpecializedBehavior : Behavior
{
    public override string GetOrderByKeySelector(Person p)
    {
        return p.LastName;
    }
}

List<Person> persons = new List<Person>
{
    new Person{Age=10, FirstName="Pelle", LastName="Larsson"},
    new Person{Age=90, FirstName="Nils", LastName="Nilsson"}, 
    new Person{Age=15, FirstName="Olle", LastName="Johansson"},
    new Person{Age=30, FirstName="Kalle", LastName="Svensson"}
};

像这样使用：

SpecializedBehavior behavior = new SpecializedBehavior();
IEnumerable<Person> orderedResult = persons.OrderBy(behavior.GetOrderByKeySelector);

Answer 1

如何将集合带入方法。

void Main()
{
    SpecializedBehavior behavior = new SpecializedBehavior();
    IEnumerable<Person> orderedResult = behavior.Sort(persons);
}

public class Person
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public int Age { get; set; }
}

public class Behavior
{
    public virtual IEnumerable<Person> Sort(IEnumerable<Person> persons)
    {
        return persons.OrderBy(p => p.FirstName);
    }
}

public class SpecializedBehavior : Behavior
{
    public override IEnumerable<Person> Sort(IEnumerable<Person> persons)
    {
        return persons.OrderBy(p => p.Age);
    }
}


List<Person> persons = new List<Person>
{
    new Person{Age=10, FirstName="Pelle", LastName="Larsson"},
    new Person{Age=90, FirstName="Nils", LastName="Nilsson"},
    new Person{Age=15, FirstName="Olle", LastName="Johansson"},
    new Person{Age=30, FirstName="Kalle", LastName="Svensson"}
};

Answer 2

这个答案只是为了说明@LasseVågsætherKarlsen的评论，所有功劳应该归功于他：

public class Person
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public int Age { get; set; }
}

public class PersonByFirstNameComparer : IComparer<Person>
{
    public int Compare(Person left, Person right) =>
        left.FirstName.CompareTo(right.FirstName);
}

public class Behavior
{
    public virtual IComparer<Person> GetComparer() => PersonByFirstNameComparer();
}

public class PersonByLastNameComparer : IComparer<Person>
{
    public int Compare(Person left, Person right) =>
        left.LastName.CompareTo(right.LastName);
}

public class SpecializedBehavior : Behavior
{
    public override IComparer<Person> GetComparer() => new PersonByLastNameComparer();
}

可以通过以下方式使用：

public static void Main()
{
    var people = new List<Person>
    {
        new Person{Age=10, FirstName="Pelle", LastName="Larsson"},
        new Person{Age=90, FirstName="Nils", LastName="Nilsson"}, 
        new Person{Age=15, FirstName="Olle", LastName="Johansson"},
        new Person{Age=30, FirstName="Kalle", LastName="Svensson"}
    };

    var standardBehavior = new Behavior();
    IEnumerable<Person> orderedPeople1 = 
        people.OrderBy(p => p, standardBehavior.GetComparer());

    foreach (Person p in orderedPeople1)
    {
        Console.WriteLine($"{p.FirstName} {p.LastName}");
    }

    var specializedBehavior = new SpecializedBehavior();
    IEnumerable<Person> orderedPeople2 = 
        people.OrderBy(p => p, specializedBehavior.GetComparer());

    foreach (Person p in orderedPeople2)
    {
        Console.WriteLine($"{p.FirstName} {p.LastName}");
    }
}

Link to fiddle

在TKey

2 个答案: