Question

Consider the code in the following example:

abstract class Car
{
    public abstract Engine CarEngine { get; protected set; }

    public Car()
    {
        CarEngine.EngineOverheating += new EventHandler(CarEngine_EngineOverheating);
    }

    void CarEngine_EngineOverheating(object sender, EventArgs e)
    {
        // Subscribing to the event of all engines
    }
}

sealed class Toyota : Car
{
    public Toyota()
    {
        this.CarEngine = new ToyotaEngine();
    }


    public override Engine CarEngine { get; protected set; }
}

abstract class Engine
{
    public event EventHandler EngineOverheating;
}

class ToyotaEngine : Engine
{

}

This code, as expected doesn’t work since CarEngine has not yet been initialized. What are my options to resolve such a case?

Several options that I see with their cons:

1. Subscribe in each child class manually – Results with a lot of boiler plate code and as a result, error-prone.
2. Initialize() function – Error-prone and redundant.

I’d be happy to see more ideas.

Thanks!

Answer 1

Create a constructor in Car taking an engine as a parameter and assign it prior to subscribing to events, like this:

abstract class Car
{
    public abstract Engine CarEngine { get; protected set; }

    public Car(Engine carEngine)
    {
        CarEngine = carEngine;
        CarEngine.EngineOverheating += new EventHandler(CarEngine_EngineOverheating);
    }

    void CarEngine_EngineOverheating(object sender, EventArgs e)
    {
        // Subscribing to the event of all engines 
    }
}

sealed class Toyota : Car
{
    public Toyota()
        : base(new ToyotaEngine())
    {
    }


    public override Engine CarEngine { get; protected set; }
}