Answers for "dependency injection"

dependency injection

Dependency injection is basically providing the objects that an object needs 
(its dependencies) instead of having it construct them itself. 

It's a very useful technique for testing, since it allows dependencies 
to be mocked or stubbed out.

dependency injection

Class A   Class B   if A uses some methods of B then its a dependency injection

dependency injection

class User 
{
    private $database = null;

    public function __construct(Database $database) {
        $this->database = $database;
    }

    public function getUsers() {
        return $this->database->getAll('users');
    }
}

$database = new Database('host', 'user', 'pass', 'dbname');
$user = new User($database);
$user->getUsers();

dependency injection

public class CustomerService
{
    CustomerBusinessLogic _customerBL;

    public CustomerService()
    {
        _customerBL = new CustomerBusinessLogic(new CustomerDataAccess());
    }

    public string GetCustomerName(int id) {
        return _customerBL.ProcessCustomerData(id);
    }
}

dependency injection

public class CustomerBusinessLogic
{
    ICustomerDataAccess _dataAccess;

    public CustomerBusinessLogic(ICustomerDataAccess custDataAccess)
    {
        _dataAccess = custDataAccess;
    }

    public CustomerBusinessLogic()
    {
        _dataAccess = new CustomerDataAccess();
    }

    public string ProcessCustomerData(int id)
    {
        return _dataAccess.GetCustomerName(id);
    }
}

public interface ICustomerDataAccess
{
    string GetCustomerName(int id);
}

public class CustomerDataAccess: ICustomerDataAccess
{
    public CustomerDataAccess()
    {
    }

    public string GetCustomerName(int id) 
    {
        //get the customer name from the db in real application        
        return "Dummy Customer Name"; 
    }
}

Dependency Injection .net

using System;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.Hosting;

namespace DependencyInjection.Example
{
    public class Worker : BackgroundService
    {
        private readonly IMessageWriter _messageWriter;

        public Worker(IMessageWriter messageWriter) =>
            _messageWriter = messageWriter;

        protected override async Task ExecuteAsync(CancellationToken stoppingToken)
        {
            while (!stoppingToken.IsCancellationRequested)
            {
                _messageWriter.Write($"Worker running at: {DateTimeOffset.Now}");
                await Task.Delay(1000, stoppingToken);
            }
        }
    }
}