Question

如果我有以下代码并希望迭代车辆列表并显示价格，我该如何访问该属性？

    public class Vehicle
    {
        public string Name { get; set; }
        public string Price { get; set; }
    }

    public class ElectricalDriven : Vehicle
    {
        public string SuperChargerCord { get; set; }
    }

    public class GasolinDriven : Vehicle
    {
        public string GasolineTank { get; set; }
    }

        var myListOfVechicles = new List<Vehicle>();
        myListOfVechicles.Add(new ElectricalDriven { Name = "Tesla", Price = "100 000", SuperChargerCord = "Yellow cord"});
        myListOfVechicles.Add(new GasolinDriven { Name = "Ford", Price = "50 000", GasolineTank = "Large VZ Tank"});


        foreach (var row in myListOfVechicles)
        {
            Console.WriteLine($"- {row.Name}");
        }

Answer 1

问题是Vehicle Value属性，因此您无法以类型安全的方式提出要求。

有些选择是：

覆盖ToString，以便类确定显示内容：
将virtual方法添加到VEhivel like GetDescription that returns a string if you don't want that string to override ToString`
将Price移至Vehicle或ElectricalDriven和GasolinDriven都继承自的子类型。

Answer 2

在foreach中，您可以使用'is'运算符检查当前'row'是ElectricalDriven还是GasolinDriven，然后将该行转换为匹配的具体实现。应该是这样的：

if (row is ElectricalDriven)
{
    Console.WriteLine($"Price: {((ElectricalDriven)row).Price}");
}
else if (row is GasolinDriven)
{
    Console.WriteLine($"Price: {((GasolinDriven)row).Price}");
}

然而，你可以看到越多不同的车辆，越多的ifs。您应该在基类或界面中移动price属性。

编辑：看到作者将price属性移动到Vehicle类，您现在可以像访问Name属性一样访问它。

Answer 3

如果要为Electric和Gasoline车辆定义一个唯一属性，并且能够从通用车辆类中检索其值，您可以声明一个虚方法并在继承类中覆盖它：

 public class Vehicle
{
    public string Name { get; set; }
    public virtual string GetCustomProperty() { return string.Empty; }
}

public class ElectricalDriven : Vehicle
{
    public string ElectricalVehicleProperty { get; set; }
    public override string GetCustomProperty() { return ElectricalVehicleProperty; }
}

public class GasolinDriven : Vehicle
{
    public string GasolinVehicleProprety { get; set; }
    public override string GetCustomProperty() { return GasolinVehicleProprety; }
}
class Program
{
    static void Main(string[] args)
    {
        var myListOfVechicles = new List<Vehicle>();
        myListOfVechicles.Add(new ElectricalDriven { Name = "Tesla", ElectricalVehicleProperty = "100 000" });
        myListOfVechicles.Add(new GasolinDriven { Name = "Ford", GasolinVehicleProprety = "50 000" });

        foreach (var row in myListOfVechicles)
        {
            Console.WriteLine("Price: " + row.GetCustomProperty()); //will output 100,000 and 50,000
        }
        Console.Read();
    }
}

Answer 4

通过这样做：

var myListOfVechicles = new List<Vehicle>();
myListOfVechicles.Add(new ElectricalDriven { Name = "Tesla", Price = "100 000" });
myListOfVechicles.Add(new GasolinDriven { Name = "Ford", Price = "50 000" });

编译器会在隐式转换为基类类型后，将子类的对象（如ElectricalDriven）分配给基类（Vehicle） 。 / p>

由于此转换，当您尝试访问该对象时，您正在访问仅具有Name基类成员的对象。

为了能够访问Price，您需要显式在访问其成员之前将对象强制转换为子类类型。最简单的例子你可以试试这个：

string name, price; foreach (var item in myListOfVechicles) { name = item is ElectricalDriven ? (item as ElectricalDriven).Name : (item as GasolinDriven).Name; price = item is ElectricalDriven ? (item as ElectricalDriven).Price : (item as GasolinDriven).Price; Console.WriteLine($"Name: {name} - Price: {price}"); }

如何从列表中访问属性

4 个答案: