C# 获取 IEnumerable 集合的个数

           IEnumerable<Attribute> keys = p.GetCustomAttributes().ToList();

  var data1 = data.Where(n => n.Name.Contains(search)).ToList();

  if (data1.Count == 0)

 //MSDN例子

using System;
using System.Windows.Forms;
using System.Collections;

namespace Exceltest
{
    public partial class Form3 : Form
    {
        public Form3()
        {
            InitializeComponent();
        }

        private void Form3_Load(object sender, EventArgs e)
        {
              MessageBox.Show("000");
            Person[] peopleArray = new Person[3]
        {
            new Person("John", "Smith"),
            new Person("Jim", "Johnson"),
            new Person("Sue", "Rabon"),
        };
            var ss = new People(peopleArray); //创建一个对象,这个对象_people属性是一个数组

            People peopleList = new People(peopleArray);
            foreach (Person p in peopleList)  //如果不集成IEnumerable,对象将无法使用foreach
                Console.WriteLine(p.firstName + " " + p.lastName);
        }
    }

    public class Person //人,个人
    {
        public Person(string fName, string lName)
        {
            this.firstName = fName;
            this.lastName = lName;
        } //构造方法
        public string firstName;
        public string lastName;
    }

    public class People : IEnumerable //人,大家
    {
        private Person[] _people; //定义一个个人数组

        public People(Person[] pArray) //构造函数需要传递过来一个数组 /////数组传递到people中
        {
            _people = new Person[pArray.Length]; //初始化数组的范围,

            for (int i = 0; i < pArray.Length; i++) 
            {
                _people[i] = pArray[i]; 
            }
        }

        IEnumerator IEnumerable.GetEnumerator() // 集成必须要实现该接口
        {
            PeopleEnum ss = new PeopleEnum(_people);

            return new PeopleEnum(_people); //返回
        }
    }

    public class PeopleEnum : IEnumerator
    {
        public Person[] _people;

        // Enumerators are positioned before the first element
        // until the first MoveNext() call.
        int position = -1;

        public PeopleEnum(Person[] list)
        {
            _people = list;
        }

        public bool MoveNext()
        {
            position++;
            return (position < _people.Length);
        }

        public void Reset()
        {
            position = -1;
        }

        public object Current
        {
            get
            {
                try
                {
                    return _people[position];
                }
                catch (IndexOutOfRangeException)
                {
                    throw new InvalidOperationException();
                }
            }
        }
    }
}