c# - ObservableCollection 上的扩展方法，MyType : IEnumerable

Question

我在为自定义类型的 ObservableCollection 创建扩展方法时遇到问题。我需要创建的扩展方法是“ToAnotherType”类型(如 ToList、ToArray)。 MyPoint 示例实现了 IEnumerable 接口(interface)，但我认为我没有正确公开 yield ？

真实的事情显然有更多的事情在发生，这只是控制台应用程序中用于识别问题的精简示例。我试过将 OC 更改为常规列表，看看那里是否发生了什么，但事实并非如此。

我看到许多“如何使您的类可枚举”示例创建了从 List 派生的第二个类(IE，public class MyPointList : List)，但是当原始类型可以自行处理或将其推送时，这似乎很浪费在部分类文件中关闭。

一切看起来都在工作，直到扩展方法本身中的 foreach - 我收到一条错误消息，指出“MyPoint”不包含“X”和“Y”的定义。

显然，我可以使用接受一个 List 并返回一个 List 的方法来处理转换，但是如果有扩展就太好了。

关于我如何完成代码的引用资料: https://www.codeproject.com/Articles/474678/A-Beginners-Tutorial-on-Implementing-IEnumerable-I

https://dotnetcodr.com/2015/07/24/implementing-an-enumerator-for-a-custom-object-in-net-c/

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Drawing;
using System.Collections;

namespace EnumerableDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            var myPoints = new ObservableCollection<MyPoint>
            {
                new MyPoint(10, 10),
                new MyPoint(20, 20),
                new MyPoint(30, 30),
                new MyPoint(40, 40),
                new MyPoint(50, 50)
            };

            Console.WriteLine("Print a single point via extension method:");
            PrintSinglePointToConsole(myPoints[0].ToPoint());

            Console.WriteLine("");
            Console.WriteLine("Print the whole OC of points:");
            PrintPointsToConsole(myPoints.ToPoints());
            Console.ReadLine();
        }

        public static void PrintSinglePointToConsole(Point point)
        {
            Console.WriteLine("Point {0},{1}", point.X, point.Y);
        }

        public static void PrintPointsToConsole(List<Point> points)
        {
            foreach (var item in points)
            {
                Console.WriteLine("Point: {0},{1}", item.X, item.Y);
            }
        }

    }

    public class MyPoint : IEnumerable<MyPoint>
    {
        private List<MyPoint> _myPoints = new List<MyPoint>();

        private int _x { get; set; } = 0;
        public int X { get { return _x; } set { _x = value; } }

        private int _y { get; set; } = 0;
        public int Y { get { return _y; } set { _y = value; } }

        public MyPoint()
        {
        }

        public MyPoint(int x, int y)
        {
            _x = x;
            _y = y;
        }

        public IEnumerator<MyPoint> GetEnumerator()
        {
            foreach (var item in _myPoints)
            {
                yield return item;
            }
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            return GetEnumerator();
        }
    }

    public static class MyPointExtension
    {
        public static Point ToPoint(this MyPoint point)
        {
            return new Point(point.X, point.Y);
        }

        public static List<Point> ToPoints<MyPoint>(this ObservableCollection<MyPoint> list)
        {
            var result = new List<Point>();

            foreach (var item in list)
            {
                //Line with error: 
                //'MyPoint' Does not contain a definition for 'X' and no extension method for
                //'X' accepting a first argument type of 'MyPoint' could be found.
                result.Add(new Point(item.X, item.Y));
            }

            return result;
        }
    }
}

Answer 1

ToPoints 中不需要MyPoint 通用参数。

就用

public static List<Point> ToPoints(this ObservableCollection<MyPoint> list)

结果是:

Print a single point via extension method:
Point 10,10

Print the whole OC of points:
Point: 10,10
Point: 20,20
Point: 30,30
Point: 40,40
Point: 50,50

顺便说一句，如果您丢弃 _x 和 _y 字段，您还可以使代码更简洁、更短，如下所示:

public int X { get; set; } = 0;
public int Y { get; set; } = 0;

public MyPoint(int x, int y)
{
    X = x;
    Y = y;
}