合并泛型方法

Question

我是 C# 新手，我有以下 3 种方法。这些方法允许调用者通过在给定方法上指定 lambda 表达式来检索表的不同属性。但是，我感觉专家会将它们进一步组合成一个通用方法。如果可以的话，请告诉我怎么做。

private KeyValuePair<T, int> GetHeaderProperty<T>(Func<Header, T> Property, 
                                                  Source ds)
{
    Func<Source, Header> GetValue =
        a => Books.Where(str => str.BookId == a.DiscardBookId)
                 .First().Header;
    return new KeyValuePair<T,int>(Property(GetValue(ds)), 0);
} 

private KeyValuePair<T, int> GetBookProperty<T>(Func<Book, T> Property,
                                               Source ds)
{
    Func<Source, Book> GetValue = 
        a => Books.Where(str => str.BookId == a.DiscardBookId).First();

    return new KeyValuePair<T, int>(Property(GetValue(ds)), 0);
} 

private KeyValuePair<T, int> GetFleetProperty<T>(Func<Fleet, T> Property,
                                                 Source ds)
{
    Func<Source,Fleet> GetValue =
        a => Books.Where(str => str.BookId == a.DiscardBookId).First()
                 .Header.Fleet;

    return new KeyValuePair<T,int>(Property(GetValue(ds)), 0);
} 

Answer 1

我认为下面将相当于连续调用所有三个方法并将结果添加到列表中：

private IEnumerable<KeyValuePair<T, int>> GetFleetProperty<T>(
                                              Func<Book, T> PropertyBook,
                                              Func<Header, T> PropertyHeader,
                                              Func<Fleet, T> PropertyFleet,
                                              Source ds)
{
    Func<Source,Fleet> GetValue =
        a => Books.Where(str => str.BookId == a.DiscardBookId).First();

    var book = GetValue(ds);
    var result = new List<KeyValuePair<T, int>>();
    result.Add(new KeyValuePair<T, int>(PropertyBook(book), 0);
    result.Add(new KeyValuePair<T, int>(PropertyHeader(book.Header), 0);
    result.Add(new KeyValuePair<T, int>(PropertyFleet(book.Header.Fleet), 0);
    return result;
} 

更新：
您还可以创建这样的方法：

private KeyValuePair<T, int> GetProperty<T, TProperty>(
                                 Func<TProperty, T> Property, 
                                 Func<Book, TProperty> GetProperty, 
                                 Source ds)
{
    Func<Source, Header> GetValue =
        a => Books.Where(str => str.BookId == a.DiscardBookId)
                 .First();
    var book = GetValue(ds);
    return new KeyValuePair<T,int>(Property(GetProperty(book)), 0);
} 

你可以这样称呼 Header：

GetProperty(xyz, b => b.Header, ds);

对于 Book，你可以这样称呼它：

GetProperty(xyz, b => b, ds);

对于 Fleet，您可以这样称呼它：

GetProperty(xyz, b => b.Header.Fleet, ds);

Answer 2

你可以使用这样的东西

public interface IPieceProvider<T>
    {
        T GetPiece();
    }

    public class Fleet
    {
        public string Test;
    }

    public class Header
    {
        public Fleet Fleet;
        public string Test;
    }

    public class Source
    {
        public int DiscardBookId;
    }

    public partial class Book
        : IPieceProvider<Book>, IPieceProvider<Header>, IPieceProvider<Fleet>
    {
        public int BookId;
        public Header Header;
        public string Test;

        Book IPieceProvider<Book>.GetPiece()
        {
            return this;
        }

        Header IPieceProvider<Header>.GetPiece()
        {
            return Header;
        }

        Fleet IPieceProvider<Fleet>.GetPiece()
        {
            return Header.Fleet;
        }
    }

    class Program
    {
        Book[] Books;

        private KeyValuePair<T, int> GetProperty<T, TP>(Func<TP, T> propertyGetter, Source ds)
        {
            return Books
                .Where(b => b.BookId == ds.DiscardBookId)
                .Cast<IPieceProvider<TP>>()
                .Select(p => p.GetPiece())
                .Select(p => new KeyValuePair<T, int>(propertyGetter(p), 0))
                .First();
        }

        static void Main(string[] args)
        {
            var source = new Source();
            var prg = new Program();
            var bookTest = prg.GetProperty((Book b) => b.Test, source);
            var headerTest = prg.GetProperty((Header h) => h.Test, source);
            var fleetTest = prg.GetProperty((Fleet f) => f.Test, source);

            Console.ReadKey();
        }
    }