static void MainA()
{
Console.WriteLine("MainClassFour -> MainA");
TrainSignal trainSignal = new TrainSignal();
new Car(trainSignal);
new Car(trainSignal);
new Car(trainSignal);
new Car(trainSignal);
trainSignal.HereComesATrain();
Console.WriteLine("***");
trainSignal.TrainsAComing();
Console.WriteLine("***");
trainSignal.TrainsAComing = null;
trainSignal.HereComesATrain();
}
public Car(TrainSignal trainSignal)
{
trainSignal.TrainsAComing += StopTheCar; // Observer pattern
}