使用變量作為類型並實例化它

Question

首先，我想說我是C＃的新手，所以這個問題似乎完全偏離了軌道。

我有一組名為ShapeType的枚舉：

Cube, Sphere, Rectangle, Ellipse

以及從枚舉中返回隨機值的方法：

private static ShapeType GetRandomShape()
{
    Array values = Enum.GetValues(typeof(ShapeType));
    Random random = new Random();
    ShapeType randomShape = (ShapeType)values.GetValue(random.Next(values.Length));
    return randomShape;
}

每個可枚舉的都有相應的具體類。 我想知道的問題是，如果你可以使用隨機可枚舉值randomShape來實例化一個類，有點像這樣：

private static Shape GetRandomShape()
{
    Array values = Enum.GetValues(typeof(ShapeType));
    Random random = new Random();
    ShapeType randomShape = (ShapeType)values.GetValue(random.Next(values.Length));
    Shape shape = new randomShape(); // *Here use the randomShape-variable as type*
    return shape;
}

這可能還是只是一廂情願的想法？

Answer 1

您可以使用字典為枚舉的每個值檢索工廠函數：

static readonly Dictionary<ShapeType, Func<Shape>> _factoryLookup = new Dictionary<ShapeType, Func<Shape>>
{
    [ShapeType.Cube] = () => new Cube(),
    [ShapeType.Ellipse] = () => new Ellipse(),
    [ShapeType.Rectangle] = () => new Rectangle(),
    [ShapeType.Sphere] = () => new Sphere(),
};

static readonly Random random = new Random();

private static Shape GetRandomShape()
{
    Array values = Enum.GetValues(typeof(ShapeType));
    ShapeType randomShape = (ShapeType)values.GetValue(random.Next(values.Length));
    Func<Shape> factory = _factoryLookup[randomShape];
    Shape shape = factory();
    return shape;
}

Answer 2

您需要使用工廠方法模式 ：

public class Shape {}

public class Cube : Shape {}

public class Sphere : Shape {}

public class Rectangle : Shape {}

public class Ellipse : Shape {}

public Shape randomShape(ShapeType shapeType)
{
    switch(shapeType)
    {
         case ShapeType.Cube:
         return new Cube();
         ...
    }
}

Answer 3

使用enumvalue作為鍵創建一個Dictionary，並鍵入value。

Dictionary<ShapeType, Type> dic = new Dictionary<ShapeType, Type>();
dic.Add(ShapeType.Cube, typeof(Cube));

// ...

private static Shape GetRandomShape()
{
    Array values = Enum.GetValues(typeof(ShapeType));
    Random random = new Random();
    ShapeType randomShape = (ShapeType)values.GetValue(random.Next(values.Length));
    Shape shape = Activator.CreateInstance(dic[randomShape]); // *Here use the randomShape-variable as type*
    return shape;
}

Answer 4

代替

enum ShapeType { Cube, Sphere, Rectangle, Ellipse }

你可以使用類似的東西

abstract class Figure
{
    protected int id;

    public static implicit operator int(Figure figure) => figure.id;
    public static implicit operator Figure(int value) => Figures().First(figure => figure.id == value);

    protected Figure(int id)
    {
        this.id = id;
    }

    public static Cube Cube { get; } = new Cube(1);
    public static Sphere Sphere { get; } = new Sphere(2);

    public static IEnumerable<Figure> Figures()
    {
        yield return Cube;
        yield return Sphere;
    }

    public override string ToString() => this.GetType().ToString();
}

class Cube : Figure
{
    public Cube(int id) : base(id) { }
}
class Sphere : Figure
{
    public Sphere(int id) : base(id) { }
}

這將讓你做類似的事情：

Console.WriteLine((object)(Figure)1); // Cube
Console.WriteLine((object)(Figure)2); // Sphere

我在許多地方使用這種方法而不是enum ，這通常是不夠的（因為它需要保存額外的信息，而不僅僅是名稱和int ）。