c# – 找不到扩展方法(不是程序集引用问题)

我有以下扩展方法：

public static EntitySet<T> ToEntitySetFromInterface<T, U>(this IList<U> source)
    where T : class, U
{
    var es = new EntitySet<T>();
    IEnumerator<U> ie = source.GetEnumerator();
    while (ie.MoveNext())
    {
        es.Add((T)ie.Current);
    }
    return es;
}

我试图使用它如下：

   List<IItemMovement> p = new List<IItemMovement>();
    EntitySet<ItemMovement> ims = p.ToEntitySetFromInterface<ItemMovement, IItemMovement>();

其中ItemMovement实现了IItemMovement.编译器抱怨：

‘System.Collections.Generic.List’ does not contain a
definition for ‘ToEntitySetFromInterface’ and no extension method
‘ToEntitySetFromInterface’ accepting a first argument of type
‘System.Collections.Generic.List’ could be found (are
you missing a using directive or an assembly reference?)

不,我没有错过参考.如果我只输入包含弹出方法的静态类的名称,那么扩展方法也是如此.日Thnx

解决方法:

这段代码适用于我,它是代码的直接副本,减去ItemMovement及其界面,所以这个部分可能有问题吗？

public class TestClient
{
    public static void Main(string[] args)
    {
        var p = new List<IItem>();
        p.Add(new Item { Name = "Aaron" });
        p.Add(new Item { Name = "Jeremy" });

        var ims = p.ToEntitySetFromInterface<Item, IItem>();

        foreach (var itm in ims)
        {
            Console.WriteLine(itm);
        }

        Console.ReadKey(true);
    }
}

public class Item : IItem
{
    public string Name { get; set; }
    public override string ToString()
    {
        return Name;
    }
}

public interface IItem
{
}

public static class ExtMethod
{
    public static EntitySet<T> ToEntitySetFromInterface<T, U>(this IList<U> source) where T : class, U
    {
        var es = new EntitySet<T>();
        IEnumerator<U> ie = source.GetEnumerator();
        while (ie.MoveNext())
        {
            es.Add((T)ie.Current);
        }
        return es;
    }
}

标签：c,linq,extension-methods
来源： https://codeday.me/bug/20190630/1334758.html