如何使用反射将未知属性正确地转换为从公共基派生的泛型列表

Question

假设我有以下内容：

public class MyContainer
{
    public string ContainerName { get; set; }
    public IList<Square> MySquares { get; set; }
    public IList<Circle> MyCircles { get; set; }
    public MyContainer()
    {
        MySquares = new List<Square>();
        MyCircles = new List<Circle>();
    }
}
public class Shape
{
    public int Area { get; set; }
}
public class Square : Shape
{
}
public class Circle : Shape
{
}

现在我有一个这样的函数：

private static void Collect(MyContainer container)
{
    var properties = container.GetType().GetProperties();
    foreach (var property in properties)
    {
        if (property.PropertyType.IsGenericType &&
            property.PropertyType.GetGenericTypeDefinition() == typeof(IList<>) &&
            typeof(Shape).IsAssignableFrom(property.PropertyType.GetGenericArguments()[0]))
        {
            var t = property.GetValue(container, null) as List<Square>;
            if (t != null)
            {
                foreach (Shape shape in t)
                {
                    Console.WriteLine(shape.Area);
                }
            }
        }
    }

当我到达MySquares属性时，这是我想要的方式，但我希望改为以下方式：

var t = property.GetValue(container, null) as List<Shape>;

我希望它能在MyContainer的所有具有类似列表的属性中循环。我有办法做到这一点吗？

Answer 1

正如我在评论中所建议的，使用协变接口可以实现这一点。

协方差/反方差：http://msdn.microsoft.com/en-us/library/ee207183.aspx
另请参阅：协方差和IList

工作样品

namespace Covariance
{
    public class MyContainer
    {
        public string ContainerName { get; set; }
        public IList<Square> MySquares { get; set; }
        public IList<Circle> MyCircles { get; set; }
        public MyContainer() {
            MySquares = new List<Square>();
            MyCircles = new List<Circle>();
        }
    }
    public class Shape
    {
        public int Area { get; set; }
    }
    public class Square : Shape
    {
    }
    public class Circle : Shape
    {
    }   
    class Program
    {
        static void Main( string[] args ) {
            MyContainer mc = new MyContainer();
            mc.MyCircles.Add( new Circle { Area = 60 } );
            Collect( mc );
            Console.ReadLine();
        }
        private static void Collect( MyContainer container ) {
            var properties = container.GetType().GetProperties();
            foreach( var property in properties ) {
                if( property.PropertyType.IsGenericType &&
                    property.PropertyType.GetGenericTypeDefinition() == typeof( IList<> ) &&
                    typeof( Shape ).IsAssignableFrom( property.PropertyType.GetGenericArguments()[0] ) ) {
                    var t = property.GetValue( container, null ) as IEnumerable<Shape>;
                    if( t != null ) {
                        foreach( Shape shape in t ) {
                            Console.WriteLine( shape.Area );
                        }
                    }
                }
            }
        }
    }
}

Answer 2

如果您将GetValue行更改为以下行，它将起作用：

var t = property.GetValue(container, null) as IEnumerable<Shape>;

我用以下代码测试了它：

var c = new MyContainer();
c.MySquares.Add(new Square() { Area = 5, });
c.MySquares.Add(new Square() { Area = 7, });
c.MySquares.Add(new Square() { Area = 11, });
c.MyCircles.Add(new Circle() { Area = 1, });
c.MyCircles.Add(new Circle() { Area = 2, });
c.MyCircles.Add(new Circle() { Area = 3, });
Collect(c);

得到了以下结果：

5
7
11
1
2
3