C#yield return用法示例

using System;
using System.Collections.Generic;

namespace Test
{
    class Program
    {
        static void Main(string[] args)
        {
            var list = new List<int> { 1, 2, 3, 4, 5, 6, 7, 8, 9 };

            var resultNormal = EvenNormal(list);
            foreach (var item in resultNormal)
            {
                Console.WriteLine(item);
            }

            var resultYieldReturn = EvenYieldReturn(list);
            foreach (var item in resultYieldReturn)
            {
                Console.WriteLine(item);
            }
        }

        static IEnumerable<int> EvenNormal(List<int> list)
        {
            var result = new List<int>();
            foreach (var item in list)
            {
                if (item % 2 == 0)
                {
                    result.Add(item);// 类似DataSet（整个结果集加载到内存中），适合少量数据的遍历
                }
            }
            return result;
        }

        static IEnumerable<int> EvenYieldReturn(List<int> list)
        {
            foreach (var item in list)
            {
                if (item % 2 == 0)
                {
                    yield return item;// 类似DataReader（读取一条返回一条），适合海量数据的遍历
                }
            }
            yield break;
        }
    }
}