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Dependency Inversion Principle In C#

This article explains the dependency inversion principle in C#.

What Does The Dependency Inversion Principle State?

According to this principle: -

High-level and low-level modules should depend on shared abstractions rather than depending directly on one another.
Abstractions should not depend on implementation details; implementation details should depend on abstractions.

Let me first explain the concept of high-level and low-level modules. In a traditional layered architecture, an application is typically divided into three main layers: **Presentation, Business, and Data Access**. The **Presentation Layer** represents the high-level module, as it defines what the application does from the user’s perspective, while the **Data Access Layer** represents the low-level module, as it deals with the implementation details of data storage and retrieval.

Example

To begin with, create the PresentationLayer and ApplicationLayer classes.

public class PresentationLayer {
  public string GetMessage() {
    ApplicationLayer applicationLayer = new ApplicationLayer();
    return applicationLayer.GetWelcomeMessage();
  }
}
public class ApplicationLayer {
  public string GetWelcomeMessage() {
    return "Welcome Karan";
  }
}

Here, the PresentationLayer class directly depends on the ApplicationLayer.

Picture showing the traditional development method where high level module is dependent on low level module

Click to Enlarge

The Dependency Inversion Principle states that: -

Define an interface.
Implement the interface in the low-level module.
Use an interface as an abstraction layer between the high-level and low-level modules.

The implementation is shown below.

public class PresentationLayer {
  IMessage _message;
  public PresentationLayer(IMessage message) {
    this._message = message;
  }

  public string GetMessage() {
    return _message.GetWelcomeMessage();
  }
}

public interface IMessage {
  string GetWelcomeMessage();
}

public class ApplicationLayer: IMessage {
  public string GetWelcomeMessage() {
    return "Welcome Karan";
  }
}

Picture showing the Dependency Inversion principle method of implementation

Click to Enlarge

Posted By -	Karan Gupta

Posted On -	Monday, December 28, 2020

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