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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 common abstractions instead of directly depending on one another.
Abstractions should remain independent of implementation details, while implementation details should rely on the abstractions.

Let me explain high-level and low-level modules. In a traditional layered architecture, an application is typically divided into presentation, business, and data access layers. The presentation layer represents the high-level module, while the data access layer represents the low-level module.

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 the interface to interact with the low-level module from the high-level module.

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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