The Inversion Of Control Principle

Manage All Your Toys in One Place

The Inversion Of Principle is the companion principle to the Dependency Inversion Principle.

The Dependency Inversion Principle creates an environment that supports management of the instantiation of assembly types at the highest level of module abstraction.

By having access to our dependencies at the module level that will be consuming the return response results, rather than the lower level module creating the response type, provides us with the opportunity to manage collections of dependencies in a centralized location.

The Centralized Management of our Types
puts “All of Our Toys” in one Place

The Inversion Of Control Principle States:

Software Dependency Instantiation Should be Managed at the Application Level

… Using Application Level Containers Provided By Higher Level Modules

Rather than having our lower class types “New Up“, create a required object, at the lowest module level we can use a Factory Pattern solution for managing our assembly instances in one location with greater control and performance.

A Design Pattern that Acts as an Object Instance Factory

… Is Called An Inversion Of Control Container, an IOC Container

The Major Advantages of IOC Containers:

1. Create a Management Solution whose Scope is at the Assembly Level

2. Manages Concretes from Abstractions created using the Dependency Inversion Principle

3. Decouples the Instantiation from the Abstractions using Concrete Resolutions

4. Manages Instantiation Life Cycle using Lifetime Management Strategies

5. Manages the Destruction of the Entities when they  Required Disposal

When types are Interfaces registered within the Container then their registered Concretes can be swapped out easily through the “Resolve” process. 

IOC Containers create Loosely Coupled Architectures that can Support Dynamic Changes at run time

Dynamic Run Time Changes to the Resolved Concrete Type

… Use a Run Time Process called Interception

…… To Swap out One Type for Another Based on Some Run Time Event

Business requirement change requests during the
Software Development Life Cycle (SDLC)
of the deployed application
are less expensive to implement

What is Dependency Injection?

Dependencies can be Passed or “Injected” to consuming Software Entities in Three Primary Ways:

1. Constructor Injection – Using the new keyword in C# to instantiate a new Type as a Parameter in a Constructor: a Class or a Method

2. Property or “Setter” Injection – Using the new keyword in C# to instantiate a new Type within the “setter” of a Class Level Property 

3. Interface Injection – Passing an Abstraction to a Type that creates the Concrete Type that implements the Interface

Inversion Of Control Container facilitate the implementation of the
Dependency Injection Design Pattern

The Inversion Of Control Principle

The Benefits of Compliance with the Inversion Of Control Principle:

1. Better Memory Management of Assembly Types

2. Vehicle for Ensuring that Single Instances of Objects are Managed Correctly 

3. Manages the Disposal of Objects when Destruction is Required

4. Encourage Coding to Abstractions Rather than Concretes

5. Creates the Ability to Change a Concrete Type During Run Time based on an Application Event

Dependency Inversion Creates Injectable Dependencies

IOC Containers Manage those Injected Dependencies

The Next Principle Design Series Post:

The Boy Scout Principle

… Always Leave the Environment You Visit

…… In Better Shape Than When You Entered It