在.NET Core Service应用程序中使用依赖注入 [英] Using Dependency Injection in .NET Core Service application

问题描述

我们在.net核心中有一个基于服务的应用程序，它将在Linux环境中作为守护程序运行。一切都按预期工作，但我在处理依赖项注入时遇到问题。
以下是参考代码

We have a service based application in .net core which would run as a daemon in Linux environment. Everything is working as expected but i am having problem in handling dependency injection. Below is the code for reference

Program.cs

Program.cs

class Program
{
    static async Task Main(string[] args)
    {
        Console.WriteLine("Starting PreProcessor Application ");


        try
        {
            ConfigParameters.LoadSettings(args);

        }
        catch (Exception ex)
        {

            Console.BackgroundColor = ConsoleColor.Red;
            Console.WriteLine($"Error in setting config parameters {ex.Message}");
            return;
        }            

        IHost host = new HostBuilder()

            .ConfigureServices((hostContext, services) =>
            {
                services.AddLogging();                    
                services.AddHostedService<MainService>();
                services.AddTransient<IMessageQueue, ActiveMQHandler>(x =>
                {
                    return new ActiveMQHandler(ConfigParameters.Settings.MessageQueueAddress);
                });
                services.AddTransient<IMessageQueue, ActiveMQHandler>(x =>
                {
                    return new ActiveMQHandler(ConfigParameters.Settings.MessageQueueAddress);
                });
                services.AddTransient<IMessageQueue, ActiveMQHandler>(x =>
                {
                    return new ActiveMQHandler(ConfigParameters.Settings.MessageQueueAddress);
                });
            })
            .Build();        

        await host.RunAsync();
    }
}

MainService的构造函数看起来像这样

IApplicationLifetime appLifetime;
    IConfiguration configuration;
    PreProcessorQueueListener listener;
    private string reason = "SHUTDOWN SIGNAL";
    private IMessageQueue messageQueue;
    private IMessageQueue messageQueueSL;
    private IMessageQueue messageQueueSLProcess;
    public MainService(IConfiguration configuration, IApplicationLifetime appLifetime, IMessageQueue messageQueue, IMessageQueue messageQueueSL, IMessageQueue messageQueueSLProcess)
    {
        this.configuration = configuration;            
        this.messageQueue = messageQueue;
        this.messageQueueSL = messageQueueSL;
        this.messageQueueSLProcess = messageQueueSLProcess;
        this.appLifetime = appLifetime;
    }

如果您在我的 MainService中看到代码我使用构造函数依赖注入为 IMessageQueue 接口传递了三个实例。我真正想要的是基于应用程序任何部分的需求，我可以通过传递 IMessageQueue ActiveMQHandler 类的新实例$ c>界面。由于我无法为此找到解决方案，因此我传递了三个实例（我对这种解决方案不满意） IMessageQueue 。如果我需要使用 ActiveMQHandler 类的另一个实例，那么我将不得不在我的<中将第四个参数作为 IMessageQueue 接口传递code> MainService 类。

If you see in my MainService code i am passing three instances for IMessageQueue interface using constructor dependency injection. What i really want is based on a need in any part of the application i could grab a new instance of ActiveMQHandler class by passing IMessageQueue interface. Since i could not find a solution for this i am passing three instances (i am not happy with this solution) of IMessageQueue. If i need to use another instance of ActiveMQHandler class then i will have to pass fourth parameter as IMessageQueue interface in my MainService class.

我真正想要的是使用 ServiceProvider （或更优雅的东西）并使用它来获得实现<的类的新实例/单例（基于 Program.cs 的定义） code> IMessageQueue 接口。

What i am really looking for is use ServiceProvider (or something more elegant) and use that to get a new / singleton (based on how it is defined in Program.cs) instance of the class which implements the IMessageQueue interface.

一个建议者？

推荐答案

只需将构造函数更改为包含 IEnumerable< IMessageQueue> 。
应该给您所有已注册的IMessageQueue实现者的列表。

Just change the constructor to contain IEnumerable<IMessageQueue>. It should give you a list of all registered IMessageQueue implementers.

我个人不喜欢在类中依赖IApplicationLifetime或IServiceProvider。这有点像ServiceLocator反模式。

Personally I do not like taking on dependencies on IApplicationLifetime or IServiceProvider in my classes. This is a bit like the ServiceLocator anti-pattern.

这篇关于在.NET Core Service应用程序中使用依赖注入的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！