c# List集合類常用操作：二、增加

所有操作基於以下類

class Employees
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string City { get; set; }
    public DateTime BirthDate { get; set; }
}

Add(T) 將對象添加到 List<T> 的結尾處。

List<Employees> employees = new List<Employees>();
employees.Add(new Employees { Id = 0, Name = "Nancy.Davolio", City = "Seattle", BirthDate = Convert.ToDateTime("1948-12-08") });
employees.Add(new Employees { Id = 1, Name = "Andrew.Fuller", City = "Tacoma", BirthDate = Convert.ToDateTime("1952-02-19") });
employees.Add(new Employees { Id = 2, Name = "Janet.Leverling", City = "Kirkland", BirthDate = Convert.ToDateTime("1963-08-30") });
employees.Add(new Employees { Id = 3, Name = "Margaret.Peacock", City = "Redmond", BirthDate = Convert.ToDateTime("1937-09-19") });
employees.Add(new Employees { Id = 4, Name = "Steven.Buchanan", City = "London", BirthDate = Convert.ToDateTime("1955-03-04") });

AddRange(IEnumerable<T>)將指定集合的元素添加到 List<T> 的末尾。

Employees[] employees =
{
    new Employees { Id = 0, Name = "Nancy.Davolio", City = "Seattle", BirthDate = Convert.ToDateTime("1948-12-08") },
    new Employees { Id = 1, Name = "Andrew.Fuller", City = "Tacoma", BirthDate = Convert.ToDateTime("1952-02-19") },
    new Employees { Id = 2, Name = "Janet.Leverling", City = "Kirkland", BirthDate = Convert.ToDateTime("1963-08-30") },
    new Employees { Id = 3, Name = "Margaret.Peacock", City = "Redmond", BirthDate = Convert.ToDateTime("1937-09-19") },
    new Employees { Id = 4, Name = "Steven.Buchanan", City = "London", BirthDate = Convert.ToDateTime("1955-03-04") }
};
List<Employees> emp = new List<Employees>();
emp.AddRange(employees);

Insert(Int32, T) 將元素插入 List<T> 的指定索引處。

 List<Employees> employees = new List<Employees>();
 employees.Add(new Employees { Id = 1, Name = "Nancy.Davolio", City = "Seattle", BirthDate = Convert.ToDateTime("1948-12-08") });
 employees.Add(new Employees { Id = 2, Name = "Andrew.Fuller", City = "Tacoma", BirthDate = Convert.ToDateTime("1952-02-19") });
 employees.Add(new Employees { Id = 3, Name = "Janet.Leverling", City = "Kirkland", BirthDate = Convert.ToDateTime("1963-08-30") });
 employees.Add(new Employees { Id = 4, Name = "Margaret.Peacock", City = "Redmond", BirthDate = Convert.ToDateTime("1937-09-19") });
 employees.Add(new Employees { Id = 5, Name = "Steven.Buchanan", City = "London", BirthDate = Convert.ToDateTime("1955-03-04") });
 //在第一個元素插入
 employees.Insert(0,new Employees { Id = 0, Name = "Michael.Suyama", City = "London", BirthDate = Convert.ToDateTime("1963-07-02") });

InsertRange(Int32, IEnumerable<T>) 將集合中的元素插入 List<T> 的指定索引處。

 List<Employees> employees = new List<Employees>();
 employees.Add(new Employees { Id = 1, Name = "Nancy.Davolio", City = "Seattle", BirthDate = Convert.ToDateTime("1948-12-08") });
 employees.Add(new Employees { Id = 2, Name = "Andrew.Fuller", City = "Tacoma", BirthDate = Convert.ToDateTime("1952-02-19") });
 Employees[] emp =
 {
     new Employees { Id = 3, Name = "Janet.Leverling", City = "Kirkland", BirthDate = Convert.ToDateTime("1963-08-30") },
     new Employees { Id = 4, Name = "Margaret.Peacock", City = "Redmond", BirthDate = Convert.ToDateTime("1937-09-19") },
     new Employees { Id = 5, Name = "Steven.Buchanan", City = "London", BirthDate = Convert.ToDateTime("1955-03-04") }
 };
 employees.InsertRange(2,emp);

List<T>在C＃中只有修改實例的void Add(T item)方法將單個項添加到列表中。
IEnumarable<T> Append(this IEnumerable<T> source, T element)另一方面，是在IEnumerable接口上定義的擴展方法（由所有列表實現）。它不會修改原始列表實例，但會返回一個新的枚舉，它將在序列的末尾生成指定的元素。

Append<TSource>(IEnumerable<TSource>, TSource) 將一個值追加到序列末尾。 

List<Employees> employees = new List<Employees>();
employees.Add(new Employees { Id = 1, Name = "Nancy.Davolio", City = "Seattle", BirthDate = Convert.ToDateTime("1948-12-08") });
employees.Add(new Employees { Id = 2, Name = "Andrew.Fuller", City = "Tacoma", BirthDate = Convert.ToDateTime("1952-02-19") });
employees = employees.Append(new Employees { Id = 3, Name = "Janet.Leverling", City = "Kirkland", BirthDate = Convert.ToDateTime("1963-08-30") }).ToList();

Prepend<TSource>(IEnumerable<TSource>, TSource) 向序列的開頭添加值。

List<Employees> employees = new List<Employees>();
employees.Add(new Employees { Id = 1, Name = "Nancy.Davolio", City = "Seattle", BirthDate = Convert.ToDateTime("1948-12-08") });
employees.Add(new Employees { Id = 2, Name = "Andrew.Fuller", City = "Tacoma", BirthDate = Convert.ToDateTime("1952-02-19") });
employees = employees.Prepend(new Employees { Id = 3, Name = "Janet.Leverling", City = "Kirkland", BirthDate = Convert.ToDateTime("1963-08-30") }).ToList();

輸出

//Id Name            City     BirthDate
//---------------------------------------------
//3  Janet.Leverling Kirkland 1963/8/30 0:00:00
//1  Nancy.Davolio   Seattle  1948/12/ 8 0:00:00
//2  Andrew.Fuller   Tacoma   1952/2/ 19 0:00:00