通过递归检查父子关系构建树类型列表 C# [英] Build tree type list by recursively checking parent-child relationship C#
问题描述
我有一个类,它有自己的列表,因此可以用树结构表示.
I have One class that has a list of itself so it can be represented in a tree structure.
我正在拉取这些类的平面列表,并希望将其展开.
I am pulling a flat list of these classes and want to unflatten it.
public class Group
{
public int ID {get;set;}
public int? ParentID {get;set;}
public List<Group> Children {get;set;}
}
我希望能够执行以下操作
I want to be able to do the following
List<Group> flatList = GetFlatList() //I CAN ALREADY DO THIS
List<Group> tree = BuildTree(flatList);
如果不明显,则 ParentID 与其父组的 ID 属性相关.
The ParentID related to the ID property on its parent group if that wasnt obvious.
编辑
对于为什么我返回列表而不是单个对象存在一些困惑.
There is some confusion as to why I am returning a list and not a single object.
我正在构建一个 UI 元素,其中包含一个项目列表,每个项目都有一个子项.所以初始列表没有根节点.到目前为止,似乎所有的解决方案都不起作用.
I am building a UI element that has a list of items, each of why has a child. So the initial list DOES NOT have a root node. It seems all of the solutions so far do not work.
这意味着我本质上需要一个使用 Group 类的树型结构列表.
What this means is I essentially need a list of tree type structures using Group class.
推荐答案
我不知道你为什么想要你的 BuildTree
方法返回 List
- tree 需要有根节点,所以你应该期望它返回单个 Group
元素,而不是一个列表.
I have no idea why you want your BuildTree
method return List<Group>
- tree needs to have root node, so you should expect it to return single Group
element, not a list.
我会在 IEnumerable
上创建一个扩展方法:
I would create an extension method on IEnumerable<Group>
:
public static class GroupEnumerable
{
public static IList<Group> BuildTree(this IEnumerable<Group> source)
{
var groups = source.GroupBy(i => i.ParentID);
var roots = groups.FirstOrDefault(g => g.Key.HasValue == false).ToList();
if (roots.Count > 0)
{
var dict = groups.Where(g => g.Key.HasValue).ToDictionary(g => g.Key.Value, g => g.ToList());
for (int i = 0; i < roots.Count; i++)
AddChildren(roots[i], dict);
}
return roots;
}
private static void AddChildren(Group node, IDictionary<int, List<Group>> source)
{
if (source.ContainsKey(node.ID))
{
node.Children = source[node.ID];
for (int i = 0; i < node.Children.Count; i++)
AddChildren(node.Children[i], source);
}
else
{
node.Children = new List<Group>();
}
}
}
使用
var flatList = new List<Group>() {
new Group() { ID = 1, ParentID = null }, // root node
new Group() { ID = 2, ParentID = 1 },
new Group() { ID = 3, ParentID = 1 },
new Group() { ID = 4, ParentID = 3 },
new Group() { ID = 5, ParentID = 4 },
new Group() { ID = 6, ParentID = 4 }
};
var tree = flatList.BuildTree();
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