访问ASP.NET Core DI容器来自静态工厂类

你可以避免使用静态类，并使用依赖注入:

• 使用IApplicationLifetime在应用程序启动/停止时启动/停止监听器。
• 使用IServiceProvider创建消息处理器实例。

public class RabbitOptions
{
    public string HostName { get; set; }
    public string UserName { get; set; }
    public string Password { get; set; }
    public int Port { get; set; }
}
// In appsettings.json:
{
  "Rabbit": {
    "hostName": "192.168.99.100",
    "username": "guest",
    "password": "guest",
    "port": 5672
  }
}

接下来，将MessageHandlerFactory转换为非静态类，该类接收作为依赖的IServiceProvider。它将使用服务提供者来解析消息处理器实例:

public class MessageHandlerFactory
{
    private readonly IServiceProvider services;
    public MessageHandlerFactory(IServiceProvider services)
    {
        this.services = services;
    }
    public IMessageProcessor Create(string messageType)
    {
        switch (messageType.ToLower())
        {
            case "ipset":
                return services.GetService<IpSetMessageProcessor>();                
            case "endpoint":
                return services.GetService<EndpointMessageProcessor>();
            default:
                throw new Exception("Unknown message type");
        }
    }
}

这样，你的消息处理器类可以在构造函数中接收它们需要的任何依赖项(只要你在Startup.ConfigureServices中配置它们)。例如，我将一个ILogger注入到我的一个示例处理器中:

public class IpSetMessageProcessor : IMessageProcessor
{
    private ILogger<IpSetMessageProcessor> logger;
    public IpSetMessageProcessor(ILogger<IpSetMessageProcessor> logger)
    {
        this.logger = logger;
    }
    public void Process(string message)
    {
        logger.LogInformation("Received message: {0}", message);
    }
}

现在将MessageListener转换为依赖于IOptions<RabbitOptions>和MessageHandlerFactory的非静态类。它与您的原始类非常相似，我只是用选项依赖项替换了Start方法的参数，处理程序工厂现在是依赖项而不是静态类:

public class MessageListener
{
    private readonly RabbitOptions opts;
    private readonly MessageHandlerFactory handlerFactory;
    private IConnection _connection;
    private IModel _channel;
    public MessageListener(IOptions<RabbitOptions> opts, MessageHandlerFactory handlerFactory)
    {
        this.opts = opts.Value;
        this.handlerFactory = handlerFactory;
    }
    public void Start()
    {
        var factory = new ConnectionFactory
        {
            HostName = opts.HostName,
            Port = opts.Port,
            UserName = opts.UserName,
            Password = opts.Password,
            VirtualHost = "/",
            AutomaticRecoveryEnabled = true,
            NetworkRecoveryInterval = TimeSpan.FromSeconds(15)
        };
        _connection = factory.CreateConnection();
        _channel = _connection.CreateModel();
        _channel.ExchangeDeclare(exchange: "myExchange", type: "direct", durable: true);
        var queueName = "myQueue";
        QueueDeclareOk ok = _channel.QueueDeclare(queueName, true, false, false, null);
        _channel.QueueBind(queue: queueName, exchange: "myExchange", routingKey: "myRoutingKey");
        var consumer = new EventingBasicConsumer(_channel);
        consumer.Received += ConsumerOnReceived;
        _channel.BasicConsume(queue: queueName, noAck: false, consumer: consumer);
    }
    public void Stop()
    {
        _channel.Close(200, "Goodbye");
        _connection.Close();
    }
    private void ConsumerOnReceived(object sender, BasicDeliverEventArgs ea)
    {
        // get the details from the event
        var body = ea.Body;
        var message = Encoding.UTF8.GetString(body);
        var messageType = "endpoint";  // hardcoding the message type while we dev...
        //var messageType = Encoding.UTF8.GetString(ea.BasicProperties.Headers["message-type"] as byte[]);
        // instantiate the appropriate handler based on the message type
        IMessageProcessor processor = handlerFactory.Create(messageType);
        processor.Process(message);
        // Ack the event on the queue
        IBasicConsumer consumer = (IBasicConsumer)sender;
        consumer.Model.BasicAck(ea.DeliveryTag, false);
    }
}

差不多了，你需要更新Startup.ConfigureServices方法，这样它就知道你的服务和选项了(如果你愿意，你可以为监听器和处理程序工厂创建接口):

public void ConfigureServices(IServiceCollection services)
{            
    // ...
    // Add RabbitMQ services
    services.Configure<RabbitOptions>(Configuration.GetSection("rabbit"));
    services.AddTransient<MessageListener>();
    services.AddTransient<MessageHandlerFactory>();
    services.AddTransient<IpSetMessageProcessor>();
    services.AddTransient<EndpointMessageProcessor>();
}

最后，更新Startup.Configure方法以获取额外的IApplicationLifetime参数并在ApplicationStarted/ApplicationStopped事件中启动/停止消息侦听器(尽管我注意到不久前使用IISExpress的applicationstop事件存在一些问题，如此问题):

public MessageListener MessageListener { get; private set; }
public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory, IApplicationLifetime appLifetime)
{
    appLifetime.ApplicationStarted.Register(() =>
    {
        MessageListener = app.ApplicationServices.GetService<MessageListener>();
        MessageListener.Start();
    });
    appLifetime.ApplicationStopping.Register(() =>
    {
        MessageListener.Stop();
    });
    // ...
}

尽管使用依赖注入是一个更好的解决方案，但在某些情况下，您必须使用静态方法(如扩展方法)

对于这些情况，你可以在静态类中添加一个静态属性，并在ConfigureServices方法中初始化它。

public static class EnumExtentions
{
    static public IStringLocalizerFactory StringLocalizerFactory { set; get; }
    public static string GetDisplayName(this Enum e)
    {
        var resourceManager = StringLocalizerFactory.Create(e.GetType());
        var key = e.ToString();
        var resourceDisplayName = resourceManager.GetString(key);
        return resourceDisplayName;
    }
}

和你的ConfigureServices:

EnumExtentions.StringLocalizerFactory = services.BuildServiceProvider().GetService<IStringLocalizerFactory>();

我知道我的答案晚了，但我想分享我是如何做到的。

首先:使用ServiceLocator是反模式的，所以尽量不要使用它。在我的例子中，我需要它在DomainModel中调用MediatR来实现DomainEvents逻辑。

然而，我必须找到一种方法来调用我的DomainModel中的静态类，以从DI获得某些注册服务的实例。

所以我决定使用HttpContext来访问IServiceProvider，但我需要从静态方法访问它，而不用在我的领域模型中提到它。

让我们开始吧:

1-我创建了一个接口来包装IServiceProvider

public interface IServiceProviderProxy
{
    T GetService<T>();
    IEnumerable<T> GetServices<T>();
    object GetService(Type type);
    IEnumerable<object> GetServices(Type type);
}

2-然后我创建了一个静态类作为我的ServiceLocator接入点

public static class ServiceLocator
{
    private static IServiceProviderProxy diProxy;
    public static IServiceProviderProxy ServiceProvider => diProxy ?? throw new Exception("You should Initialize the ServiceProvider before using it.");
    public static void Initialize(IServiceProviderProxy proxy)
    {
        diProxy = proxy;
    }
}

3-我已经为IServiceProviderProxy创建了一个实现，它在内部使用IHttpContextAccessor

public class HttpContextServiceProviderProxy : IServiceProviderProxy
{
    private readonly IHttpContextAccessor contextAccessor;
    public HttpContextServiceProviderProxy(IHttpContextAccessor contextAccessor)
    {
        this.contextAccessor = contextAccessor;
    }
    public T GetService<T>()
    {
        return contextAccessor.HttpContext.RequestServices.GetService<T>();
    }
    public IEnumerable<T> GetServices<T>()
    {
        return contextAccessor.HttpContext.RequestServices.GetServices<T>();
    }
    public object GetService(Type type)
    {
        return contextAccessor.HttpContext.RequestServices.GetService(type);
    }
    public IEnumerable<object> GetServices(Type type)
    {
        return contextAccessor.HttpContext.RequestServices.GetServices(type);
    }
}

public void ConfigureServices(IServiceCollection services)
{
    services.AddHttpContextAccessor();
    services.AddSingleton<IServiceProviderProxy, HttpContextServiceProviderProxy>();
    .......
}

5-最后一步是在应用程序启动时用IServiceProviderProxy的实例初始化ServiceLocator

public void Configure(IApplicationBuilder app, IHostingEnvironment env,IServiceProvider sp)
{
    ServiceLocator.Initialize(sp.GetService<IServiceProviderProxy>());
}

作为结果，现在你可以调用ServiceLocator在你的DomainModel类"或和需要的地方"，并解决你需要的依赖。

public class FakeModel
{
    public FakeModel(Guid id, string value)
    {
        Id = id;
        Value = value;
    }
    public Guid Id { get; }
    public string Value { get; private set; }
    public async Task UpdateAsync(string value)
    {
        Value = value;
        var mediator = ServiceLocator.ServiceProvider.GetService<IMediator>();
        await mediator.Send(new FakeModelUpdated(this));
    }
}

以下是我对你的案例的看法:

如果可能的话，我将发送解析服务作为参数

public static IMessageProcessor Create(string messageType, IIpSetService ipService)
{
    //
}

否则使用寿命将是重要的。

如果服务是单例的，我只需要设置依赖于configure方法:

 // configure method
public IApplicationBuilder Configure(IApplicationBuilder app)
{
    var ipService = app.ApplicationServices.GetService<IIpSetService>();
    MessageHandlerFactory.IIpSetService = ipService;
}
// static class
public static IIpSetService IpSetService;
public static IMessageProcessor Create(string messageType)
{
    // use IpSetService
}

如果服务生命周期是有范围的，我将使用HttpContextAccessor:

//Startup.cs
public void ConfigureServices(IServiceCollection services)
{
    services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();
}
public IApplicationBuilder Configure(IApplicationBuilder app)
{
    var httpContextAccessor= app.ApplicationServices.GetService<IHttpContextAccessor>();
    MessageHandlerFactory.HttpContextAccessor = httpContextAccessor;
}
// static class
public static IHttpContextAccessor HttpContextAccessor;
public static IMessageProcessor Create(string messageType)
{
    var ipSetService = HttpContextAccessor.HttpContext.RequestServices.GetService<IIpSetService>();
    // use it
}

这是一个很好的解释和ServiceLocator的一些代码，它也使用范围。所以将工作，甚至IHttpContextAccessor!

把这个类复制到你的代码中。然后注册ServiceLocator

 ServiceActivator.Configure(app.ApplicationServices);

重要提示: ServiceLocator被认为是反模式，所以如果你有任何其他选择，不要使用它!!!!

关于瓦希德·比塔尔的回答

神奇!对于。net Core 6，我在Program.cs:

builder.Services.AddSingleton<IServiceProviderProxy, HttpContextServiceProviderProxy>();
ServiceLocator.Initialize(app.Services.GetService<IServiceProviderProxy>());

您可以在Configure中获取业务参考:

app.UseMvc();
var myServiceRef = app.ApplicationServices.GetService<MyService>();

，然后将其传递给init函数或在类上设置静态成员

当然，依赖注入是一个更好的解决方案，正如其他答案所解释的那样…