How Can I Manually Resolve Instances in ASP.NET Core's `ConfigureServices()` Method?

ASP.NET Core Dependency Injection: Manually Resolving Instances in ConfigureServices()

Mastering manual instance resolution within ASP.NET Core MVC's dependency injection system, specifically within the ConfigureServices() method, provides granular control over service management. While IServiceCollection simplifies service registration (e.g., using AddTransient), it doesn't directly support instance resolution. This article explores techniques for resolving instances without relying on constructor injection.

Direct resolution within ConfigureServices() is not straightforward. The IServiceCollection offers a BuildServiceProvider() method to create a temporary IServiceProvider. This allows access to services registered before the BuildServiceProvider() call, but not to services registered subsequently. This limitation is crucial to understand.

An alternative, mirroring the functionality of the options pattern, involves binding configuration values directly to an instance. This can be achieved using the Bind() method on your IConfiguration section. For example, you could bind values from IConfiguration to an instance of MyOptions.

It's important to emphasize that resolving services within ConfigureServices() generally constitutes an anti-pattern often referred to as the "Service Locator" pattern. This practice is generally discouraged. However, specific scenarios, particularly within framework or infrastructure components, may necessitate this approach. Careful consideration should be given before employing this method.

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