c# - 获取树中的所有 child

Question

有一个存储元素树的类。子元素存放在

public List<BaseTreeData> Child { get; set; }

我想将这棵树显示为所有元素的“平面”(线性)列表。将类分成两个(基类和继承类)后，GetChildren 方法会生成有关类型不匹配的错误。很可能一切都是合乎逻辑的，但如何解决呢？

Error CS1503 Argument 1: cannot convert from 'ConsoleApplication1.BaseTreeData' to 'ConsoleApplication1.TreeData'

namespace ConsoleApplication1
{
    class Program
    {        
        static void Main(string[] args)
        {
            var data = new List<TreeData>();
            for (int i = 0; i < 5; i++)
            {
                var item = new TreeData() { Name = i.ToString() };
                for (int j = 0; j < 3; j++)
                {
                    var number = (i + 1) * 10 + j;
                    item.Child.Add(new TreeData() { ID = number, Name = number.ToString(), Parent = item });                    
                }
                data.Add(item);
            }

            foreach (var item in data.SelectMany(x => GetChildren(x)))
            {
                Console.WriteLine(item.ID + " " + item.Name + " " + item.IsChecked);
            }
        }

        static IEnumerable<TreeData> GetChildren(TreeData d)
        {
            return new[] { d }.Concat(d.Child).SelectMany(x => GetChildren(x));
        }
    }

    class BaseTreeData
    {
        public bool IsChecked { get; set; }
        public BaseTreeData Parent { get; set; }
        public List<BaseTreeData> Child { get; set; }

        public BaseTreeData()
        {
            Child = new List<BaseTreeData>();
        }
    }

    class TreeData : BaseTreeData
    {
        public int ID { get; set; }
        public string Name { get; set; }
    }
}

Answer 1

Error CS1503 Argument 1: cannot convert from 'ConsoleApplication1.BaseTreeData' to 'ConsoleApplication1.TreeData'

发生此错误是因为子节点是 BaseTreeData 而不是 TreeData。

使用您发布的 BaseTreeData 类定义，child 和 parent 将始终返回基类型。

相反，您可以使用泛型来解决这个问题，这样子节点将与父类具有相同的类型:

class BaseTreeData<T> where T : BaseTreeData<T>
{
    public bool IsChecked { get; set; }
    public T Parent { get; set; }
    public List<T> Children { get; set; }

    public BaseTreeData()
    {
        Children = new List<T>();
    }

    public IEnumerable<T> GetAncestors()
    {
        if (Parent == null)
            yield break;

        T relative = Parent;
        while (relative != null)
        {
            yield return relative;
            relative = relative.Parent;
        }
    }

    public IEnumerable<T> GetDescendants()
    {
        var nodes = new Stack<T>();
        nodes.Push(this as T);

        while (nodes.Any())
        {
            var current = nodes.Pop();
            yield return current;

            foreach (var childNode in current.Children)
                nodes.Push(childNode);
        }
    }
}

class TreeData : BaseTreeData<TreeData>
{
    public int ID { get; set; }
    public string Name { get; set; }
}