c# 依賴注入

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Reflection;
using Microsoft.Extensions.DependencyInjection;

namespace WpfApp1
{
    /// <summary>
    /// MainWindow.xaml 的交互邏輯
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            var sc = new ServiceCollection();
            sc.AddScoped(typeof(IPerson), typeof(Student));
            sc.AddScoped<DaStudent>();
            var sp = sc.BuildServiceProvider();
            var student2 = sp.GetService<DaStudent>();

            student2.SayStudent();
        }
         
    }
    
    class DaStudent
    {
        IPerson _person;

        public DaStudent(IPerson person)   //這裏必須要要有構造函數
        {
            _person = person;
        }

        public void SayStudent()
        {
            _person.say();
        }
    }
    class Student : IPerson
    {
        public int a = 12;
        public void say()
        {
            Console.WriteLine(a.ToString());
        }
    }
    interface IPerson
    {
        void say();
    }
}