Breaking and Declaring Dependencies

First part

There are two parts to the DI pattern. The first is that I remove any dependencies on concrete classes from my component—in this case PasswordResetHelper. I do this by creating a class constructor that accepts implementations of the interfaces
I need as arguments, like this:

• Remove 

1. any dependencies from my component—in this case PasswordResetHelper

• Create 

1.  a class constructor that accepts implementations of the interfaces

public class PasswordResetHelper {
private IEmailSender emailSender;
public PasswordResetHelper(IEmailSender emailSenderParam) {
emailSender = emailSenderParam;
}
public void ResetPassword() {
// ...call interface methods to configure e-mail details...
emailSender.SendEmail();
}
}

By creating a class constructor that accept implementations of the interfaces I can remove any dependency.

Second part 

The second part of the DI pattern is to inject the dependencies declared by the PasswordResetHelper class when I

create instances of it, hence the term dependency injection.

• create

1.  instances

•  declared

1. By the PasswordResetHelper 

• inject 

1. the dependencies

All this really means is that I need to decide which class that implements the IEmailSender interface I am going to use,

create an object from that class and then pass the object as an argument to the PasswordResetHelper constructor.