Question

   This violates Dependency inversion principle in SOLID programming, can someone explain why and refactor this to look correct?

 public class Computer : IPowerState
    {
        public bool IsOn { get; set; }
        public void TurnOn() { }
        public void TurnOff() { }
    }
    public class Button
    {
        public Computer _computer { get; set; };
        public Button()
        {
            _computer = new Computer();
        }
        public void Press()
        {
            if (_computer != null)
            {
                if (_computer.IsOn)
                    _computer.TurnOff();
                else
                    _computer.TurnOn();
            }
        }
    }

Answer 1

Reason :

In the code, the Button class uses the concrete Computer class.  ****Therefore, it is still tightly coupled.

Dependency Inversion Principle(DIP): a high-level module should not depend on low-level modules. Both should depend on abstraction. So, first, decide which is the high-level module (class) and the low-level module. A high-level module is a module that depends on other modules.

In the above code, Button depends on the Computer class, so Button class is a high-level module and the Computer class is a low-level module. So, as per the first rule of DIP, Button should not depend on the concrete Computer class, instead, both classes should depend on abstraction.

I hope it answers your problem. Also, do upvote the solution.