I'm using ABP framework. I wrote a manager in the domian layer. Do I need to inherit an interface?

In the ABP framework, it is usually recommended to use interfaces on the manager class of the Domain layer todefine the contract. The advantage of this is that it can enhance the testability and loose coupling of the code. By defining an interface, you can ensure that the manager class follows specific behaviors and constraints, and you can easily unit test and mock objects.

In addition, using interfaces can also help implement interface-based programming, which allows you to write more flexible and scalable code by relying on abstractions rather than concrete implementations.

Although it is not necessary to inherit interfaces in the ABP framework, using interfaces can provide better code organization, maintainability and scalability. Therefore, it is strongly recommended to use interfaces on the manager class of the Domain layer.

So ABP's dependency injection is not implemented through interfaces? For example, if I dependency inject this manager in the appservice layer, how is this dependency injection implemented?

In the ABP framework, dependency injection is implemented through interfaces. ABP uses an open source dependency injection container called "Castle Windsor" to manage the creation and parsing of objects.

First, you need to declare your dependency on the Manager interface in the AppService class. Typically, you declare dependencies in the constructor, for example:

public class MyApplicationService : ApplicationService
{
    private readonly IMyManager _myManager;

    public MyApplicationService(IMyManager myManager)
    {
        _myManager = myManager;
    }

    //...
}

Then, in the configuration file of the ABP framework (such asStartup.cs), you need to configure dependency injection and register related services. The specific method is to call in the ConfigureServices method and configure dependency injection, for example: services.AddAbp()

public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddApplication<MyApplicationModule>();
    }
}

In the above code, the AddApplication method specifies the application module to be registered, and it configures the dependency injection container (Castle Windsor) to use the mapping between interfaces and implementations .

In this way, when the ABP framework needs to create an MyApplicationService instance, it will automatically parse the constructor parameters of the class and use the dependency injection container to create and provide IMyManagerExample.

Please note that when using dependency injection, the ABP framework automatically handles the object's life cycle and scope. You can use the Transient, Scoped or Singleton attributes on the interface definition. Control the life cycle of objects.

To sum up, the ABP framework implements dependency injection through interfaces and uses the Castle Windsor container to manage dependencies. You only need to declare your dependency on the interface, configure it appropriately in the configuration file, and then the ABP framework will be responsible for parsing and providing related instances.

So can I understand that if I write a manager in the domian layer, but this manager does not inherit the interface, then the appservice layer cannot dependency inject this manager?

Yes, according to the convention of the ABP framework, if you create a Manager class in the Domain layer without letting it inherit the interface, then the AppService layer cannot use this Manager directly through dependency injection.

The ABP framework recommends using interfaces to abstract services to achieve loose coupling and testability. By defining the Manager class as an implementation of the interface, you can easily declare dependence on the interface in AppService and parse and use it through dependency injection.

Of course, in special cases, if you really need to use a Manager class in the AppService layer that does not inherit the interface, you can still manually instantiate and call the class in other ways. However, this approach may lead to increased coupling of the code and affect testing.

Therefore, according to the best practices of the ABP framework, it is recommended that you try to define the Manager class as an implementation of the interface in the Domain layer to better take advantage of the advantages of dependency injection and the functions provided by the framework.

In special cases, if you really need to use a Manager class in the AppService layer that does not inherit the interface, you can still manually instantiate and call the class through other means. What is this special situation?

Special circumstances may include the following:

Third-party libraries or frameworks require direct use of the Manager class instead of an interface: Some third-party libraries or frameworks may not provide an interface and can only use a specific class directly. In this case, you may need to manually instantiate and call this Manager class in the AppService layer.
Temporary requirements or rapid prototype development: In the case of some temporary requirements or rapid prototype development, in order to save time and energy, there may be no need to create an interface for the time being, and use the Manager class directly in the AppService layer to implement functions.
Specific business logic requirements: Some specific business logic may not be fully abstracted and defined through the interface, and a specific Manager class needs to be used directly in the AppService layer to meet the requirements.

Please note that using a Manager class that does not inherit the interface in the above special cases may increase the coupling of the code, make unit testing difficult, and reduce the maintainability of the code. Therefore, you should try to follow the recommended practice of the ABP framework and define the Manager class as an implementation of the interface in order to better utilize dependency injection and the functions provided by the framework.