ตัวกำหนดค่าเริ่มต้นของออบเจ็กต์และคอลเลกชัน

ตัวเริ่มต้นออบเจ็กต์คืออะไร

using System;

class Person
{
    public string Name { get; set; }
    public int Age { get; set; }
}

class Program
{
    static void Main()
    {
        var p = new Person { Name = "Ada", Age = 36 };
        Console.WriteLine(p.Name + ", " + p.Age);
    }
}

ไวยากรณ์ของตัวเริ่มต้น

using System;

class Car
{
    public string Make { get; set; }
    public string Model { get; set; }
    public int Year { get; set; }
}

class Program
{
    static void Main()
    {
        var car = new Car
        {
            Make = "Toyota",
            Model = "Corolla",
            Year = 2022
        };
        Console.WriteLine(car.Year + " " + car.Make + " " + car.Model);
    }
}

การใช้คอนสตรักเตอร์ร่วมกับตัวเริ่มต้น

using System;

class Widget
{
    public string Id { get; }
    public string Label { get; set; }

    public Widget(string id) { Id = id; }
}

class Program
{
    static void Main()
    {
        var w = new Widget("w1") { Label = "Submit" };
        Console.WriteLine(w.Id + ": " + w.Label);
    }
}

การเริ่มต้นเฉพาะบางพร็อพเพอร์ตี

using System;

class Settings
{
    public bool DarkMode { get; set; } = false;
    public int Volume { get; set; } = 50;
    public string Lang { get; set; } = "en";
}

class Program
{
    static void Main()
    {
        var s = new Settings { DarkMode = true };
        Console.WriteLine(s.DarkMode + ", " + s.Volume + ", " + s.Lang);
    }
}

ตัวเริ่มต้นคอลเลกชัน

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        var nums = new List<int> { 1, 2, 3, 4, 5 };
        Console.WriteLine("Count: " + nums.Count);
        Console.WriteLine("Sum: " + Sum(nums));
    }

    static int Sum(List<int> list)
    {
        int t = 0;
        foreach (var n in list) t += n;
        return t;
    }
}

ตัวเริ่มต้นคอลเลกชันทำงานอย่างไร

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        var names = new List<string> { "Ann", "Bob", "Cara" };
        foreach (var n in names)
            Console.WriteLine(n);
    }
}

ตัวเริ่มต้นดิกชันนารี

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        var ages = new Dictionary<string, int>
        {
            ["Ann"] = 30,
            ["Bob"] = 25
        };
        Console.WriteLine("Ann is " + ages["Ann"]);
    }
}

ตัวเริ่มต้นออบเจ็กต์แบบซ้อนกัน

using System;

class Address
{
    public string City { get; set; }
}

class Customer
{
    public string Name { get; set; }
    public Address Home { get; set; } = new Address();
}

class Program
{
    static void Main()
    {
        var c = new Customer
        {
            Name = "Lin",
            Home = new Address { City = "Tokyo" }
        };
        Console.WriteLine(c.Name + " in " + c.Home.City);
    }
}

คอลเลกชันของออบเจ็กต์

using System;
using System.Collections.Generic;

class Item
{
    public string Name { get; set; }
    public decimal Price { get; set; }
}

class Program
{
    static void Main()
    {
        var cart = new List<Item>
        {
            new Item { Name = "Pen", Price = 1.5m },
            new Item { Name = "Book", Price = 9.0m }
        };
        decimal total = 0;
        foreach (var i in cart) total += i.Price;
        Console.WriteLine("Total: " + total);
    }
}

ตัวเริ่มต้นและพร็อพเพอร์ตี init

using System;

class Config
{
    public string Env { get; init; }
    public int Retries { get; init; }
}

class Program
{
    static void Main()
    {
        var c = new Config { Env = "prod", Retries = 3 };
        Console.WriteLine(c.Env + " / " + c.Retries);
    }
}

นำทุกอย่างมารวมกัน

using System;
using System.Collections.Generic;

class Team
{
    public string Name { get; set; }
    public List<string> Members { get; set; } = new List<string>();
}

class Program
{
    static void Main()
    {
        var t = new Team
        {
            Name = "Alpha",
            Members = { "Ann", "Bob", "Cara" }
        };
        Console.WriteLine(t.Name + " has " + t.Members.Count + " members");
    }
}

ตรวจสอบความเข้าใจ

ทบทวน

using System;
using System.Collections.Generic;

class Demo
{
    public string Name { get; set; }
    public List<int> Nums { get; set; } = new List<int>();
}

class Program
{
    static void Main()
    {
        var d = new Demo { Name = "x", Nums = { 1, 2, 3 } };
        Console.WriteLine(d.Name + " " + d.Nums.Count);
    }
}