我有三门课;实现接口 IProduct 的 Stamp、Letter 和 Parcel,它们也有一些自己的功能。
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; } }
}
为什么我不能从 a 访问派生类的其他成员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);
}
我曾想过使用泛型,但在这种情况下,我将不得不为每种特定类型的产品编写单独的代码。
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);
}
这种问题没有任何设计模式吗?工厂模式?