Using Dependency Injection Containers

Introduction

Using a dependency injection container, we can avoid manually implementing dependency injection. A dependency injection container is an object that knows how to instantiate and configure objects. To do this, it needs to know about the constructor arguments and the relationships between the classes.

This lesson will demonstrate that test code remains largely the same irrespective of whether the loosely coupled application code uses manual DI or a DI container.

Brief overview of DI containers

A DI container is a library that provides DI facilities. It simplifies object composition and service lifetime management by resolving and managing object dependencies.

DI containers can analyze the requested class and determine the required dependencies at runtime. There are numerous third-party DI container frameworks, in addition to Microsoft’s own. Here, we’ll use the built-in Microsoft.Extensions.DependencyInjection library.

The steps involved in implementing DI using Microsoft’s built-in DI container are to create a service collection and add services to the collection. After adding a service provider, we can access services according to some predefined scope.

Let’s see how we can use the Microsoft.Extensions.DependencyInjection DI container framework in the implementation of a loosely coupled BankAccount class and how this facilitates unit testing.

An example of using a DI container

Suppose we have a BankAccount class that includes an Amount field. The Withdraw and Deposit methods contained in the BankAccountService class allow for withdrawing and depositing funds to and from the specified ...