c# - 方法返回泛型 func c#

Question

是否可以从一个方法返回一个通用的 Func？我想要做的是类似于下面的 GetSortFunc。

public class Example
{
    private List<MyObject> _objects;
    public Example()
    {
        _objects = new List<MyObject>
                        {
                            new MyObject {Id = 1, Name = "First", Value = 100.0},
                            new MyObject {Id = 2, Name = "Second", Value = 49.99},
                            new MyObject {Id = 3, Name = "Third", Value = 149.99}
                        };
    }

    public void Sort(SomeEnum sortOptions)
    {
        _objects = _objects.OrderBy(GetSortFunc(sortOptions));
    }

    private Func<MyObject, TKey> GetSortFunc(SomeEnum sortOptions)
    {
        switch (sortOptions)
        {
            case SomeEnum.First:
                return x => x.Id;
            case SomeEnum.Second:
                return x => x.Name;
            case SomeEnum.Third:
                return x => x.Value;
        }
    }
}

SomeEnum 和 MyObject 看起来像这样:

public enum SomeEnum
{
    First,
    Second,
    Third
}

public class MyObject
{
    public int Id { get; set; }
    public string Name { get; set; }
    public double Value { get; set; }
}

这是可能的还是我走错了路？

Answer 1

问题是返回类型会随着 TKey 的类型而变化。此外，OrderBy 的类型参数也会有所不同。我建议您只复制 OrderBy 调用:

IEnumerable<MyObject> ApplySortOrder(IEnumerable<MyObject> items, SomeEnum sortOptions)
{
    switch (sortOptions)
    {
        case SomeEnum.First:
            return items.OrderBy(x => x.Id);
        case SomeEnum.Second:
            return items.OrderBy(x => x.Name);
        case SomeEnum.Third:
            return items.OrderBy(x => x.Value);
    }
}

或者，让 GetSortFunc 返回 delegate 并动态调用 OrderBy:

private Delegate GetSortFunc(SomeEnum sortOptions)
{
    switch (sortOptions)
    {
        case SomeEnum.First:
            return new Func<MyObject, int>(x => x.Id);
        case SomeEnum.Second:
            return new Func<MyObject, string>(x => x.Name);
        case SomeEnum.Third:
            return new Func<MyObject, int>(x => x.Value);
    }
}

//...

Enumerable.OrderBy(_objects, (dynamic)GetSortFunc(sortOptions));

这将在运行时选择正确的重载。