c# - 通用嵌套类型:无法从X <T>转换为X <T>

我正在编写用于处理无向图的类，并且遇到以下编译时错误：


  最佳重载方法匹配
  'Dictionary.EdgeCollection> .Add（TVertex，UndirectedGraph.EdgeCollection）'
  有一些无效的论点
  
  参数2：无法转换
  来自UndirectedGraph<TVertex,TEdge>.AdjacentEdgeCollection<TVertex,TEdge>
    到UndirectedGraph<TVertex,TEdge>.AdjacentEdgeCollection<TVertex,TEdge>


我可以将问题简化为以下示例：

public class UndirectedGraph<TVertex, TEdge>
{
    Dictionary<TVertex, EdgeCollection<TVertex, TEdge>> edges;

    class VertexCollection<TVertex, TEdge>
    {
        UndirectedGraph<TVertex, TEdge> graph;

        public VertexCollection(UndirectedGraph<TVertex, TEdge> graph)
        { this.graph = graph; }

        public void Add(TVertex value)
        {
            // Argument 2: cannot convert
            // from 'UndirectedGraph<TVertex,TEdge>.AdjacentEdgeCollection<TVertex,TEdge>'
            //   to 'UndirectedGraph<TVertex,TEdge>.AdjacentEdgeCollection<TVertex,TEdge>'
            this.graph.edges.Add(value, new EdgeCollection<TVertex, TEdge>(this.graph));
        }
    }

    class EdgeCollection<TVertex, TEdge>
    {
        public EdgeCollection(UndirectedGraph<TVertex, TEdge> graph) { }
    }
}

请注意，嵌套类中的TVertex和TEdge与外部类中的TVertex和TEdge不同，并且我收到警告，指出应重命名它们。我可以做到，但这不会影响错误。我认为该片段的目的很明确，那么我如何使它做我想做的事情以及我的想法在哪里出错呢？

最佳答案

您确定存在三个TVertex类型参数和三个TEdge类型参数吗？在我看来这三个都是相同的，您需要的是以下内容：

public class UndirectedGraph<TVertex, TEdge>
{
    Dictionary<TVertex, EdgeCollection> edges;

    class VertexCollection
    {
        UndirectedGraph<TVertex, TEdge> graph;

        public VertexCollection(UndirectedGraph<TVertex, TEdge> graph)
        { this.graph = graph; }

        public void Add(TVertex value)
        {
            this.graph.edges.Add(value, new EdgeCollection(this.graph));
        }
    }

    class EdgeCollection
    {
        public EdgeCollection(UndirectedGraph<TVertex, TEdge> graph) { }
    }
}