将list转成tree

using System;
using System.Collections.Generic;
using System.Linq;

namespace Infrastructure
{
/// <summary>
/// List转成Tree
/// <para></para>
/// </summary>
public static class GenericHelpers
{
/// <summary>
/// Generates tree of items from item list
/// </summary>
///
/// <typeparam name="T">Type of item in collection</typeparam>
/// <typeparam name="K">Type of parent_id</typeparam>
///
/// <param name="collection">Collection of items</param>
/// <param name="idSelector">Function extracting item's id</param>
/// <param name="parentIdSelector">Function extracting item's parent_id</param>
/// <param name="rootId">Root element id</param>
///
/// <returns>Tree of items</returns>
public static IEnumerable<TreeItem<T>> GenerateTree<T, K>(
this IEnumerable<T> collection,
Func<T, K> idSelector,
Func<T, K> parentIdSelector,
K rootId = default(K))
{
foreach (var c in collection.Where(u =>
{
var selector = parentIdSelector(u);
return (rootId == null && selector == null)
|| (rootId != null &&rootId.Equals(selector));
}))
{
yield return new TreeItem<T>
{
Item = c,
Children = collection.GenerateTree(idSelector, parentIdSelector, idSelector(c))
};
}
}
/// <summary>
/// 把数组转为逗号连接的字符串
/// </summary>
/// <param name="data"></param>
/// <param name="Str"></param>
/// <returns></returns>
public static string ArrayToString(dynamic data, string Str)
{
string resStr = Str;
foreach (var item in data)
{
if (resStr != "")
{
resStr += ",";
}

if (item is string)
{
resStr += item;
}
else
{
resStr += item.Value;

}
}
return resStr;
}
}
}

using System.Collections.Generic;

namespace Infrastructure
{
public class TreeItem<T>
{
public T Item { get; set; }
public IEnumerable<TreeItem<T>> Children { get; set; }
}
}