我有三个班;实现接口IProduct的邮票,信件和包裹,他们也有自己的一些功能。如何从界面访问派生类成员?
public interface IProduct
{
string Name { get; }
int Quantity { get; set; }
float Amount { get; }
}
public class Stamp : IProduct
{
public string Name { get { return "Stamp"; } }
public int Quantity { get; set; }
public float Amount { get; set; }
public float UnitPrice { get; set; }
}
public class Letter : IProduct
{
public string Name { get { return "Letter"; } }
public int Quantity { get; set; }
public float Amount { get; set; }
public float Weight { get; set; }
public string Destination { get; set; }
}
public class Parcel : IProduct
{
public string Name { get { return "Parcel"; } }
public int Quantity { get; set; }
public float Amount { get; set; }
public float Weight { get; set; }
public string Destination { get; set; }
public int Size { get; set; }
}
public static class ShoppingCart
{
private static List<IProduct> products = new List<IProduct>();
public static List<IProduct> Items { get { return products; } }
}
为什么我不能访问派生类的其他成员从List<IProduct>
?
ShoppingCart.Items.Add(new Stamp { Quantity = 5, UnitPrice = 10, Amount = 50 });
ShoppingCart.Items.Add(new Letter { Destination = "US", Quantity = 1, Weight = 3.5f });
ShoppingCart.Items.Add(new Parcel { Destination = "UK", Quantity = 3, Weight = 4.2f, Size = 5 });
foreach (IProduct product in ShoppingCart.Items)
{
Console.WriteLine("Name: {0}, Quantity: {1}, Amount: {2}", product.Name, product.Quantity, product.Amount);
}
我想使用泛型的,但在这种情况下,我将必须编写单独的代码对于每个特定类型的产品。
public static class ShoppingCart<T> where T : IProduct
{
private static List<T> items = new List<T>();
public static List<T> Items { get { return items; } }
}
ShoppingCart<Stamp>.Items.Add(new Stamp { Quantity = 5, Amount = 10, UnitPrice = 50 });
ShoppingCart<Letter>.Items.Add(new Letter { Destination = "US", Quantity = 1, Weight = 3.5f });
foreach (Stamp s in ShoppingCart<Stamp>.Items)
{
Console.WriteLine("Name: {0}, Quantity: {1}, Amount: {2}", s.Name, s.Quantity, s.Amount);
}
foreach (Letter l in ShoppingCart<Letter>.Items)
{
Console.WriteLine("Name: {0}, Destination: {1}, Weight: {2}", l.Name, l.Destination, l.Weight);
}
这种问题没有任何一种设计模式。工厂模式?
我的问题是你的接口的要点是什么,如果它只有成员而不是方法?你只是在每个班级重新定义这些成员。 – JonH 2009-11-23 13:12:02
接口有必要有方法吗? – 2009-11-23 13:16:42
不,这不是必要的,但通常你使用接口来遵守合同。合同通常是需要通过签署合同的类来实施的方法。在签名者必须实现它们的界面中有方法时。当谈到变量本身,只有变量才有意义创建一个接口? – JonH 2009-11-23 13:18:29