Dependency Injection

• If no Dependency Injection, customer point to DatabaseHelper now, future have XMLDatabase, you would change lot of code.
• Dependency Injection is good; it makes the classes loose couple.
• It achieves Dependency Inversion Principle. (High-level modules should not depend on low-level modules. Both should depend on abstractions.) [Customer is High Level, DatabaseHelper is low level, IStorage is High Level]
• Is to pass the variable into Constructor, Default Constructor is to initialize the concrete class.

static void Main(string[] args)

{

       var customera = new Customer(new DatabaseHelper());

       customera.CustStore();

       var customerb = new Customer(new XMLHelper());

       customerb.CustStore();

       Console.ReadLine();

}

public class Customer

{

    private IStorageHelper _iStorageHelper;

    public Customer(IStorageHelper iStorageHelper)

    {

        _iStorageHelper = iStorageHelper;

    }

    public void CustStore()

    {

        _iStorageHelper.Store();

    }

}

public interface IStorageHelper

{

    void Store();

}

public class DatabaseHelper : IStorageHelper

{

    public void Store()

    {

        Console.WriteLine("DB Store");

    }

}

public class XMLHelper : IStorageHelper

{

    public void Store()

    {

        Console.WriteLine("XML Store");

    }

}