C#•3w ago

✅ meaning on dependency injection in C#

Hello guys, I was just reading a bit, I came across those terms "dependency injection". Can someone explain what this mean please. I read a bit about it, what I read is that dependency injection is used to prevent "tight coupling" (don't know what this is). Is dependency injection same as when we are importing libraries, like .NET libraries? Would really appreciate if someone can give simple code example of with and without dependency injection of what happen

8 Replies

Angius•3w ago

Simple example (not actual code)

var container = new DependencyContainer();
container.AddSingleton<IMailer, GmailMailer>();
container.AddSingleton<ThingyDoer>();

var container = new DependencyContainer();
container.AddSingleton<IMailer, GmailMailer>();
container.AddSingleton<ThingyDoer>();

public class ThingyDoer(IMailer mailer)
{
    public void DoTheThing()
    {
        mailer.Send("Thing has been done");
    }
}

public class ThingyDoer(IMailer mailer)
{
    public void DoTheThing()
    {
        mailer.Send("Thing has been done");
    }
}

It lets you do a few things: 1. Control the lifetime of the dependencies (per instance, per request, per app run, etc) 2. Swap the dependencies freely (change that <IMailer, GmailMailer> to <IMailer, ProtonMailMailer> and everything that requests IMailer will use ProtonMailMailer now)

Angius•3w ago

https://learn.microsoft.com/en-us/dotnet/core/extensions/dependency-injection

Dependency injection - .NET

Learn how to use dependency injection within your .NET apps. Discover how to registration services, define service lifetimes, and express dependencies in C#.

Angius•3w ago

"Loose coupling" here means that ThingyDoer does not create its own new GmailMailer(), but rather is given an already existing instance of it Or an instance of any other IMailer

FakerOP•3w ago

Is it correct to say that the idea of using dependencing injection is that instead of a class creating a specific instance of a class, assume we have 2 classes, student and person. if we have class person, instead of directly creating an instance of class student inside person (let say we require student to do stuff on it) , we want a way to make this "student" type more flexible in case we no longer want a student but rather another instance type? by the way, here, a dependency means an instance of a class? let say we have 3 classes, teacher, student and person. if in main, we write the following:

Teacher newTeacher = new Teacher();
Student newStudent = new Student();
Person newPerson = new Person(newTeacher);

Teacher newTeacher = new Teacher();
Student newStudent = new Student();
Person newPerson = new Person(newTeacher);

This is dependency injection ?

Jimmacle•3w ago

dependency injection itself just means passing objects that a new object needs to function in its constructor, so yes this moves the responsibility of "knowing" what types of objects to use from the new object to the code creating it

FakerOP•3w ago

yeah I see, was what I said correct pls

SleepWellPupper•3w ago

Hey @Faker I see you're on quite the learning journey from all your posts. If you want to read more about DI, I can highly recommend this book: https://www.oreilly.com/library/view/dependency-injection-principles/9781617294730/ It is in my opinion one of the best books any dotnet (or OOP in general) developer should read.

O’Reilly Online Learning

Dependency Injection Principles, Practices, and Patterns

FakerOP•3w ago

yep I will have a look, thanks !

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✅ meaning on dependency injection in C#

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