.NET异步编程

服务定位器

using Microsoft.Extensions.DependencyInjection;
ServiceCollection services = new();
services.AddScope<xxx>();
service.AddSingleton<xxx>();
service.AddTransient<xxx>();

不要在长生命周期的对象中引用比它生命周期短的对象。在ASP.NET中，这样做会抛出异常。

如果类无状态，建议为Singleton；如果类有状态，且有Scope控制，建议为Scope，因为通常这种Scope控制下的代码都是运行在同一线程中的，没有并发修改的问题；在使用Transient的时候要谨慎。

using (ServiceProvider serviceProvider = services.BuildServiceProvider())
{
    using (IServiceScope scope = serviceProvider.CreateScope())
    {
        TestServiceImpl t = scope.ServiceProvider.GetService<TestServiceImpl>();
    }
}

如果一个类实现了IDisposable接口，则离开Scope后会自动调用对象的Dispose方法。

DI的传染性

using Microsoft.Extensions.DependencyInjection;

ServiceCollection services = new();
services.AddScoped<Controller>();
services.AddScoped<ILog, LogImpl>();
services.AddScoped<IConfig, ConfigImpl>();
services.AddScoped<IStorage, StorageImpl>();

using (ServiceProvider serviceProvider = services.BuildServiceProvider())
{
    serviceProvider.GetRequiredService<Controller>().Test();
}

class Controller
{
    private readonly ILog log;
    private readonly IStorage storage;
    public Controller(ILog log, IStorage storage)
    {
        this.log = log;
        this.storage = storage;
    }

    public void Test()
    {
        log.Log("开始上传");
        storage.Save("----------", "1.txt");
        log.Log("写入完毕");
    }
}

interface ILog
{
    void Log(string message);
}

class LogImpl : ILog
{
    public void Log(string message)
    {
        Console.WriteLine(message);
    }
}

interface IConfig
{
    string GetValue(string key);
}

class ConfigImpl : IConfig
{
    public string GetValue(string key)
    {
        return $"{key}: hello";
    }
}

interface IStorage
{
    void Save(string content, string name);
}

class StorageImpl : IStorage
{
    private readonly IConfig config;

    public StorageImpl(IConfig config)
    {
        this.config = config;
    }
    public void Save(string content, string name)
    {
        string server = config.GetValue("server");
        Console.WriteLine($"文件{name}发送内容为{content}");
    }
}

DI综合案例

需求

有配置服务、日志服务，然后再开发一个邮件发送器服务。可以通过配置服务来从文件、环境变量、数据库等地方读取配置，可以通过日志服务来将程序运行过程中的日志信息写入文件、控制台、数据库等。

实现

创建四个类库项目，ConfigService是配置服务的项目，LogService是日志服务的项目，MailService是邮件发送器的项目，然后再建一个.NET控制台项目MailSender来调用MailService。MailService项目引用ConfigService项目和LogService项目，而MailSender项目引用MailService项目。

编写类库项目LogServices，创建ILogProvider接口。

namespace LogService;

public interface ILoggerProvider
{
    void LogError(string msg);
    void LogInformation(string msg);
}

编写实现类ConsoleLogProvider。

namespace LogService;

class ConsoleLoggerProvider : ILoggerProvider
{
    public void LogError(string msg)
    {
        Console.WriteLine($"[ERROR] {msg}");
    }

    public void LogInformation(string msg)
    {
        Console.WriteLine($"[INFO] {msg}");
    }
}

编写一个ConsoleLogProviderExtensions定义扩展方法AddConsoleLog，命名空间为Microsoft.Extensions.DependencyInjection。

using LogService;

namespace Microsoft.Extensions.DependencyInjection;

public static class ConsoleLogExtension
{
    public static void AddConsoleLog(this IServiceCollection services)
    {
        services.AddScoped<ILoggerProvider, ConsoleLoggerProvider>();
    }
}

编写配置服务的类库项目ConfigService。接口IConfigService。

using LogService;

namespace Microsoft.Extensions.DependencyInjection;

public static class ConsoleLogExtension
{
    public static void AddConsoleLog(this IServiceCollection services)
    {
        services.AddScoped<ILoggerProvider, ConsoleLoggerProvider>();
    }
}

环境变量读取配置类EnvVarConfigProvider。

namespace ConfigService;

public class EnvVarConfigService : IConfigService
{
    public string? GetValue(string key)
    {
        return Environment.GetEnvironmentVariable(key);
    }
}

定义扩展方法。

using ConfigService;

namespace Microsoft.Extensions.DependencyInjection;

public static class EnvVarConfigExtension
{
    public static void AddEnvVarConfig(this IServiceCollection services)
    {
        services.AddScoped<IConfigService, EnvVarConfigService>();
    }
}

编写从ini文件中读取配置的类IniFileConfigServices以及对应扩展方法。

namespace ConfigService;

public class IniFileConfigService : IConfigService
{
    public string FilePath { get; set; }

    public IniFileConfigService(string filePath)
    {
        FilePath = filePath;
    }

    public string? GetValue(string key)
    {
       var pair=File.ReadAllLines(FilePath)
            .Select(s => s.Split('='))
            .Select(s => new { Key = s[0], Value = s[1] })
            .SingleOrDefault(p => p.Key == key);

        return pair?.Value;
    }
}

using ConfigService;

namespace Microsoft.Extensions.DependencyInjection;

public static class LayeredConfigExtension
{
    public static void AddLayeredConfig(this IServiceCollection services)
    {
        services.AddScoped<IConfigReader,LayeredConfigReader>();
    }
}

实现“可覆盖的配置读取器”，配置文件覆盖环境变量。定义一个从各个ConfigService中读取项的IConfigReader接口。编写实现类LayeredConfigReader以及对应的扩展方法。

namespace ConfigService;

public interface IConfigReader
{
    string? GetValue(string key);
}

namespace ConfigService;

internal class LayeredConfigReader : IConfigReader
{
    private readonly IEnumerable<IConfigService> services;

    public LayeredConfigReader(IEnumerable<IConfigService> services)
    {
        this.services = services;
    }

    public string? GetValue(string key)
    {
        string? value = null;
        foreach (var service in services)
        {
            string? newValue = service.GetValue(key);
            if (newValue != null)
            {
                value = newValue;
            }
        }
        return value;
    }
}

using ConfigService;

namespace Microsoft.Extensions.DependencyInjection;

public static class LayeredConfigExtension
{
    public static void AddLayeredConfig(this IServiceCollection services)
    {
        services.AddScoped<IConfigReader,LayeredConfigReader>();
    }
}

编写发送邮件的服务。IMailService接口，实现类IMailSenderImpl。注入IConfigReader ，ILoggerProvider 。不真的发邮件，想真的发邮件用MailKit。

namespace MailService;

public interface IMailService
{
    void Send(string title, string to, string body);
}

using ConfigService;
using LogService;

namespace MailService;

public class MailServiceImpl : IMailService
{
    private readonly ILoggerProvider logger;
    private readonly IConfigReader config;

    public MailServiceImpl(ILoggerProvider logger, IConfigReader config)
    {
        this.logger = logger;
        this.config = config;
    }

    public void Send(string title, string to, string body)
    {
        logger.LogInformation("准备发送邮件");
        string? smtpServer = config.GetValue("SmtpServer");
        string? userName = config.GetValue("UserName");
        Console.WriteLine($"已发送\n【SMTP服务器】{smtpServer}\n【用户名】{userName}");
        logger.LogInformation("邮件发送完成");
    }
}

using ConfigService;
using MailService;
using Microsoft.Extensions.DependencyInjection;

ServiceCollection services = new();
services.AddEnvVarConfig();
services.AddIniFileConfig("mail.ini");
services.AddScoped<IMailService, MailServiceImpl>();
services.AddConsoleLog();
services.AddLayeredConfig();
using (var sp = services.BuildServiceProvider())
{
    // 第一个对象只能用ServiceLocator
    var mailService = sp.GetRequiredService<IMailService>();
    mailService.Send("Hello", "joe@joe.com", "你好");
}