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从c中的平面列表创建嵌套列表#

.net c#

lem.mallari · 技术社区 · 6 年前

我目前有以下课程:

public class NavigationItem
{
    public int ID { get; set; }
    public string Title { get; set; }
    public int ParentID { get; set; }
    public List<NavigationItem> Children { get; set; }
}

public class FlatItem
{
    public int ID { get; set; }
    public string Title { get; set; }
    public int ParentID { get; set; }
}

我有一个样本数据如下:

+====+============+==========+
| ID |   Title    | ParentID |
+====+============+==========+
|  1 | Google     |          |
+----+------------+----------+
|  2 | Microsoft  |          |
+----+------------+----------+
|  3 | Oracle     |          |
+----+------------+----------+
|  4 | Gmail      |        1 |
+----+------------+----------+
|  5 | Sheets     |        1 |
+----+------------+----------+
|  6 | Adsense    |        1 |
+----+------------+----------+
|  7 | Azure      |        2 |
+----+------------+----------+
|  8 | SharePoint |        2 |
+----+------------+----------+
|  9 | Office     |        2 |
+----+------------+----------+
| 10 | Java       |        3 |
+----+------------+----------+
| 11 | Word       |        9 |
+----+------------+----------+
| 12 | Excel      |        9 |
+----+------------+----------+
| 13 | PowerPoint |        9 |
+----+------------+----------+

我已经有了从上面的示例数据中提取所有信息并将其转换为 List<FlatItem> 对象。

最好的方法是什么? List<NavigationItem> 对象,其外观如下所示:

谷歌
- Gmail
- 希茨
- AdSense
微软
- 蔚蓝
- 共享点
- 办公室
  - 词
  - 擅长
  - 幻灯片演示文稿软件
甲骨文公司
- 爪哇

我正在考虑创建一个递归方法来遍历 列表<扁平项> 然后将其结构为一个导航项的嵌套列表。

4 回复 | 直到 6 年前

ViRuSTriNiTy 6 年前

不需要递归。可以使用linq轻松构建结构:

List<FlatItem> flatItems = ...;

var navigationItems = flatItems.Select(
    i => new NavigationItem { ID = i.ID, Title = i.Title, ParentID = i.ParentID }
).ToList();

foreach (var i in navigationItems)
    i.Children = navigationItems.Where(n => n.ParentID == i.ID).ToList();

// get Google, Microsoft, Oracle items
var rootNavigationItems = navigationItems.Where(n => n.ParentID == 0);

TheGeneral 6 年前

未经测试,但你可以试试这个,应该也相当快

var list = new List<FlatItem>();
var result = new List<NavigationItem>();

// just a helper to remember ids
var dict = new Dictionary<int, NavigationItem>();

foreach (var item in list)
{
   var nav = new NavigationItem()
                  {
                     ID = item.ID,
                     ParentID = item.ParentID,
                     Title = item.Title,
                     Children = new List<NavigationItem>()                                   
                  };

   if (!dict.ContainsKey(nav.ParentID))
      result.Add(nav);       
   else
      dict[nav.ParentID].Children.Add(nav);

   dict.Add(item.ID, nav);
}

Konamiman 6 年前

如果可以使用递归,则可以创建如下函数:

public List<NavigationItem> ChildrenOf(List<FlatItem> flatItems, int parentId)
{
    var childrenFlatItems = flatItems.Where(i => i.ParentID == parentId);
    return childrenFlatItems.Select(i => new NavigationItem {
        ID = i.ID,
        Title = i.Title,
        ParentID = i.ParentID, 
        Children = ChildrenOf(flatItems, i.ID)})
    .ToList();
}

然后,假设您的根项的父ID为0(因为您没有使用可为空的类型),您将生成包含以下内容的完整列表:

ChildrenOf(flatsItems, 0)

Enigmativity 6 年前

试试这个:

List<FlatItem> source = new List<UserQuery.FlatItem>()
{
    new FlatItem() { ID = 1, Title = "Google", ParentID = null },
    new FlatItem() { ID = 2, Title = "Microsoft", ParentID = null },
    new FlatItem() { ID = 3, Title = "Oracle", ParentID = null },
    new FlatItem() { ID = 4, Title = "Gmail", ParentID = 1 },
    new FlatItem() { ID = 5, Title = "Sheets", ParentID = 1 },
    new FlatItem() { ID = 6, Title = "Adsense", ParentID = 1 },
    new FlatItem() { ID = 7, Title = "Azure", ParentID = 2 },
    new FlatItem() { ID = 8, Title = "SharePoint", ParentID = 2 },
    new FlatItem() { ID = 9, Title = "Office", ParentID = 2 },
    new FlatItem() { ID = 10, Title = "Java", ParentID = 3 },
    new FlatItem() { ID = 11, Title = "Word", ParentID = 9 },
    new FlatItem() { ID = 12, Title = "Excel", ParentID = 9 },
    new FlatItem() { ID = 13, Title = "PowerPoint", ParentID = 9 },
};

var lookup = source.ToLookup(x => x.ParentID);

Func<int?, List<NavigationItem>> build = null;
build = pid =>
    lookup[pid]
        .Select(x => new NavigationItem()
        {
            ID = x.ID,
            Title = x.Title,
            ParentID = x.ParentID,
            Children = build(x.ID)
        })
        .ToList();

启动进程调用 build(null) . 这让我想到:

这确实假设 ParentId 财产是 int? -你的数据表确实建议。