I'm currently working on a project, where I have a blueprint for how my Worker class is defined, the Worker class is located in a SharedLibraryModel in a different solution folder.

 public class Worker : BackgroundService
        {
        private readonly Controller _controller;
        private string ListenQueueName;

        public Worker(Controller controller, string listenQueueName)
        {
            _controller = controller;
            ListenQueueName = listenQueueName;
        }

        protected override async Task ExecuteAsync(CancellationToken stoppingToken)
        {
          
        }

I have also made a Controller class and IController interface.

 public class Controller : IController
    {
        public (string, string) MessageReceived(string inMessage)
       {
        return ('some', 'string')
       };
  
    }

I want to use the above definition of a Worker class in my CustomerWorker, which I have defined as

public class CustomerWorker : SharedModelLibrary.Worker
    {
        public CustomerController _customerController;
        public readonly string ListenQueueName = 'customers';

        public CustomerWorker(CustomerController _customerController, string ListenQueueName)
            : base(_customerController, ListenQueueName)
        {

        }

The CustomerController inherits from the Controller.

But when the following is called in Program.cs

builder.Services.AddSingleton<ICustomerMessage, CustomerService>(); 
builder.Services.AddSingleton<CustomerController>();
builder.Services.AddHostedService<CustomerWorker>();

var app = builder.Build();

I get the error message

"Some services are not able to be constructed (Error while validating the service
descriptor 'ServiceType: Microsoft.Extensions.Hosting.IHostedService Lifetime: Singleton
 ImplementationType: CustomerMicroService.CustomerWorker': Unable to resolve service for type 
'System.String' while attempting to activate 'CustomerMicroService.CustomerWorker'.)"

I'm not sure if its improper use of inheritance or something I have misunderstood in regard to the AddHostedService and AddSingleton.

Any help would be much appreciated.

CodePudding user response：

The error message is very clear. Unable to resolve service for type 'System.String', It seems you want to inject string ListenQueueName into CustomerWorker class. but you have not register string type. I know it is impossible to register string type. I don't know the ListenQueueName purpose. you have two way to solve your issue.

1. register Customerworker by handle like below:

builder.Services.AddHostedService<CustomerWorker>(sp => 
{
   var customerController = sp.GetRequiredService<CustomerController>();

  return new CustomerWorker(customerController, "ListenQueueName");

});

2. wrapper your ListenQueueName into a class and then register that class.