[C#] 初始化器和構造函數

一. 初始化器的簡單使用

using System;

namespace 初始化器
{
    class Program
    {
        static void Main(string[] args)
        {
            //1. 常見的初始化方式，將類實例化，並通過構造函數將參數傳遞進類中，此方式通過 public StudentName(string first, string last)生效
            var student1 = new StudentName("Meimei", "Wang");

            //2. 沒有小括號，直接通過大括號調用類的屬性，並將賦值，此即為對象的初始化器，此方式通過 public StudentName() { }
            var student2 = new StudentName { FirstName = "Meimei", LastName = "Wang" };

            //3. 初始化器也就是默認的構造函數，因而可以用來對任意公共屬性進行操作，而指定的構造函數指定按照類中指定的結構進行操作
            var student3 = new StudentName { ID = 5 };  //student3 = new StudentName(100) 這是錯誤的

            //4. 另外構造函數和初始化器可以一起使用
            var student4 = new StudentName("Lei", "Li") { ID = 122 };

            Console.WriteLine(student1.ToString());
            Console.WriteLine(student2.ToString());
            Console.WriteLine(student3.ToString());
            Console.WriteLine(student4.ToString());

            Console.ReadKey();
        }
    }

    public class StudentName
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public int ID { get; set; }

        public StudentName() { }    //初始化器，其實也就是默認的構造函數

        public StudentName(string first, string last)  //該類構造函數
        {
            FirstName = first;
            LastName = last;
        }

        public override string ToString()
        {
            return FirstName + " " + ID;
        }
    }
}

二、匿名類的初始化器的使用

using System;
using System.Collections.Generic;
using System.Linq;

namespace 初始化器
{
    class Program
    {
        static void Main(string[] args)
        {
            var pet = new { Age = 10, Name = "Miaomiao" };
            //匿名類中的屬性都是只讀的
            //pet.Name = 100;  此處編譯會出錯

            //匿名類初始化器常用語LINQ語句中
            var students = new List<StudentName> { new StudentName("Li", "LI"), new StudentName("Mei", "MEI") };
            var studentsFrom = new List<StudentFrom> 
            { 
                new StudentFrom { FirstName = "Li", City = "Beijing" }, 
                new StudentFrom { FirstName = "Wang", City = "Shanghai" } 
            };

            var joinQuery = from s in students
                            join f in studentsFrom on s.FirstName equals f.FirstName
                            select new { FirstName = s.FirstName, LastName = s.LastName, City = f.City };

            foreach(var i in joinQuery)
            {
                Console.WriteLine("{0} {1} {2}", i.FirstName, i.LastName, i.City);
            }


            Console.ReadKey();
        }
    }

    public class StudentName
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public int ID { get; set; }

        public StudentName() { }    //初始化器，其實也就是默認的構造函數

        public StudentName(string first, string last)  //該類構造函數
        {
            FirstName = first;
            LastName = last;
        }

        public override string ToString()
        {
            return FirstName + " " + ID;
        }
    }

    public class StudentFrom
    {
        public string FirstName { get; set; }
        public string City { get; set; }
    }
}

三、集合類初始化器

using System;
using System.Collections.Generic;
using System.Linq;

namespace 初始化器
{
    class Program
    {
        static void Main(string[] args)
        {
            //集合的初始化器
            CollectionInitializer();

            Console.ReadKey();
        }

        private static void CollectionInitializer()
        {
            var students = new List<StudentName> 
            { 
                new StudentName { FirstName = "Mei", LastName = "MEI", ID = 100 }, //使用對象的初始化器創建
                new StudentName() { FirstName = "Lei", LastName = "LEI", ID = 101 }, //使用默認的構造函數+初始化器
                new StudentName("Li", "LI") { ID = 102 }, //使用指定的構造函數+初始化器
                null
            };

            foreach(var i in students)
            {
                if (i != null)
                {
                    Console.WriteLine(i.ToString());
                }
            }

            Dictionary<int, StudentName> studentDic = new Dictionary<int, StudentName>
            {
                { 111, new StudentName { FirstName = "Mei", LastName = "MEI", ID = 100 } },
                { 112, new StudentName() { FirstName = "Lei", LastName = "LEI", ID = 101 } },
                { 113, new StudentName("Li", "LI") { ID = 102 } }
            };

            foreach(var s in studentDic)
            {
                Console.WriteLine(s.Value.ToString());
            }
        }
    }

    public class StudentName
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public int ID { get; set; }

        public StudentName() { }    //初始化器，其實也就是默認的構造函數

        public StudentName(string first, string last)  //該類構造函數
        {
            FirstName = first;
            LastName = last;
        }

        public override string ToString()
        {
            return FirstName + " " + ID;
        }
    }

}