合并通用方法

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。然而，我有一种感觉，专家会将它们进一步组合成一个通用方法。如果可能的话，请告诉我如何做。

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

我认为以下内容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);
} 

对于 Header，您可以这样称呼它：

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

对于 Book，您可以这样称呼它：

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();
        }
    }