摘要

C# 是一种广泛使用的编程语言，具有丰富的特性和广泛的应用场景。其中，依赖注入（DI）是一种非常重要的软件设计模式，它可以将类及其依赖项的控制权反转，使得程序的可扩展性和灵活性得到了极大的提升。在 .NET 世界中，依赖注入、IConfiguration、ILogger 和 Option 模式被视为一等公民，成为了广泛使用的设计模式。

正文

nuget安装

Microsoft.Extensions.DependencyInjection;

Microsoft.Extensions.Configuration

Microsoft.Extensions.Logging

Microsoft.Extensions.Configuration.Json

Microsoft.Extensions.Logging.Console

写一个简单配制文件application.json

C#
{
  "server": "127.0.0.1",
  "user": "sa",
  "password": "123"
}

写一个DIConfig类

C#
public class DIConfig
{
    public static IServiceProvider ConfigureServices()
    {
        var serviceCollection = new ServiceCollection();
        var configuration = new ConfigurationBuilder()
            .SetBasePath(AppContext.BaseDirectory)
            .AddJsonFile("application.json",true)
            .Build();

        serviceCollection.AddSingleton(configuration);

        serviceCollection.AddLogging(loggingBuilder =>
        {
            loggingBuilder.AddConsole();
        });

        Register(serviceCollection, configuration);

        return serviceCollection.BuildServiceProvider();

    }
    
    //注册
    private static void Register(IServiceCollection services, IConfiguration configuration)
    {
        services.AddSingleton<IWriter,MessageWriter>();
        services.AddSingleton(typeof(Message<>));
        services.AddSingleton<Email>();

        services.AddSingleton(sp =>
        {
            var user = configuration.GetSection("user").Value;
            return new Func<string>(() =>
            {
                return user;
            });
        });
    }

这里Func注入，其实就是注入一个需返回的委托做为初使化，可以像一个工厂的作用。

IWriter接口

C#
public interface IWriter
{
    public void Write(string value);
}

MessageWriter，继承IWriter接口，其中添加了一个Logger

C#
public class MessageWriter: IWriter
{
    private readonly ILogger<MessageWriter> logger;

    public MessageWriter(ILogger<MessageWriter> logger)
    {
        this.logger = logger;
    }

    public void Write(string msg)
    {
         logger.LogInformation(msg);
    }
}

Email 类

C#
public class Email  
{
    private readonly IWriter _writer;
    private readonly Func<string> _func;

    public Email(IWriter writer,Func<string> func)
    {
        _writer = writer;
        _func = func;
    }   

    public void Send()
    {
        var ret = _func();
        _writer.Write("from email...");
    }
}

Message类

C#
public class Message<T>
{
    private readonly ILogger<Message<T>> logger;
    private readonly IWriter writer;

    public Message(ILogger<Message<T>> logger, IWriter writer)
    {
        this.logger = logger;
        this.writer = writer;
    }

    public void Send()
    {
        writer.Write("message t writer...");
        logger.LogInformation("message");
    }

}

调用

C#
static void Main(string[] args)
{
    var sp = DIConfig.ConfigureServices();
    var msg = sp.GetService<Email>();
    msg.Send();

    var msg1= sp.GetService<Message<String>>();
    msg1.Send();
}