Consumer 类用作事件侦听器。这个类订阅了 CarDealer 类的事件,并定义了 NewCarlsHere 方法,该方法满足 EventHandler<CarInfoEventArge>委托的要求,该委托的参数类型是 object 和 CarInfoEventArgs:.
public class Consumer
{
private string_name;
public Consumer(string name)=> _name = name;
public void NewCarIsHere(object sender, CarInfoEventArgs e)
{
Console.WriteLine($"{_name}: car {e.Car} is new")
}
}
class Program
{
static void Main()
{
var dealer = new CarDealer();
var valtteri = new Consumer("Valtteri");
dealer.NewCarInfo += valtteri.NewCarIsHere;
dealer.NewCar("Williams");
var max = new Consumer("Max");
dealer.NewCarInfo += max.NewCarIsHere;
dealer.NewCar("Mercedes");
dealer.NewCarInfo -= valtteri.NewCarIsHere;
dealer.NewCar("Ferrari");
}
}
运行应用程序,一辆 Williams 汽车到达,Valtteri 得到了通知。因为之后 Max 也注册了该订阅,所以 Valtteri 和 Max 都获得了新款 Mercedes 汽车的通知。接着 Valtteri 取消了订阅,所以只有 Max 获得了 Ferrari 汽车的通知:
CarDealer, new car Williams
Valtteri: car Williams is new
CarDealer, new car Mercedes
Valtteri: car Mercedes is new
Max: car Mercedes is new
CarDealer, new car Ferrari
Max: car Ferrari is new