为什么有时两个对象引用相同但不总是相同
为什么有时两个对象引用相同但不总是相同
提问于 2019-02-18 20:53:49
下面是最后一个答案：Recursive method to convert flat collection to hierarchal collection?
我想对层次结构之外的另一个对象使用相同的方法CreateTree : ItemNode：
public class ItemNode
{
public string Id { get; set; }
public Item Item { get; set; }
public ICollection<ItemNode> Children { get; set; }
}以及项目的定义：
public class Item
{
public string ID { get; set; }
public string Name { get; set; }
public int Level { get; set; }
public string ParentId { get; set; }
}下面是带有ItemNode的CreateTree方法：
static List<ItemNode> CreateTreeItems(IEnumerable<ItemNode> nodes)
{
Dictionary<string,ItemNode> idToNode = nodes.ToDictionary(n => n.Id, n => n);
List<ItemNode> roots = new List<ItemNode>();
ItemNode root = null;
foreach (var n in nodes)
{
if (n.Item.ParentId == null)
{
if (root != null)
{
roots.Add(root);
}
root = n;
continue;
}
ItemNode parent = idToNode[n.Item.ParentId];
//if (!idToNode.TryGetValue(n.Item.ParentId, out parent))
//{
// //Parent doesn't exist, orphaned entry
//}
parent?.Children.Add(n);
// RETURNS FALSE WHEREAS IN THE ORIGINAL METHOD IT RETURNS TRUE
var test = Object.ReferenceEquals(parent, root);
Debug.WriteLine(test);
}
if (root == null)
{
//There was no root element
}
roots.Add(root);
return roots;
}它不起作用，因为父对象和根对象不引用相同的对象(而在原始方法中，它引用了)。我猜这是因为我向ItemNode类添加了一个Item属性。但我不知道该怎么解决它。
谢谢！
回答 1
Stack Overflow用户
回答已采纳
发布于 2019-02-18 21:54:43
为什么您期望根节点和父节点引用相等？每个根节点都可能是父节点，但并非每个父节点都是根节点。
可能会出现引用相等的情况，但这在很大程度上取决于nodes集合的排序顺序。实际上，当根节点放置在第一级子节点之前时，您将看到引用相等的情况。
我认为您的问题出在其他地方，例如，如果Nodes集合根本没有根节点，它可能无法工作。
这是一个例子，在这里试试https://dotnetfiddle.net/4r52xP
using System;
using System.Collections.Generic;
using System.Linq;
public class Hierarchy
{
public Hierarchy(string iD, string name, int level, string parentID, string topParent)
{
ID = iD;
Name = name;
Level = level;
ParentID = parentID;
Children = new HashSet<Hierarchy>();
}
public string ID { get; set; }
public string Name{ get; set; }
public int Level { get; set; }
public string ParentID { get; set; }
public ICollection<Hierarchy> Children { get; set; }
}
public class Program
{
static Hierarchy CreateTree(IEnumerable<Hierarchy> Nodes)
{
var idToNode = Nodes.ToDictionary(n => n.ID, n => n);
Hierarchy root = null;
foreach (var n in Nodes)
{
if (n.ParentID == null)
{
if (root != null)
{
//there are multiple roots in the data
}
root = n;
continue;
}
Hierarchy parent = null;
if (!idToNode.TryGetValue(n.ParentID, out parent))
{
//Parent doesn't exist, orphaned entry
}
parent.Children.Add(n);
Console.WriteLine("ReferenceEquals: {0}", Object.ReferenceEquals(parent, root));
}
if (root == null)
{
//There was no root element
}
return root;
}
public static void Main()
{
Console.WriteLine("Test #1");
List<Hierarchy> l = new List<Hierarchy>();
l.Add(new Hierarchy("295152","name1",1,null, null)); // <-root node at the top of the list
l.Add(new Hierarchy("12345","child1",2,"295152", null));
l.Add(new Hierarchy("54321","child2",2,"295152", null));
l.Add(new Hierarchy("44444","child1a",3,"12345", null));
l.Add(new Hierarchy("33333","child1b",3,"12345", null));
l.Add(new Hierarchy("22222","child2a",3,"54321", null));
l.Add(new Hierarchy("22221","child2b",3,"54321", null));
l.Add(new Hierarchy("22002","child2c",3,"54321", null));
l.Add(new Hierarchy("20001","child2a2",4,"22222", null));
l.Add(new Hierarchy("20101","child2b2",4,"22222", null));
CreateTree(l);
Console.WriteLine("\nTest #2");
l = new List<Hierarchy>();
l.Add(new Hierarchy("12345","child1",2,"295152", null));
l.Add(new Hierarchy("54321","child2",2,"295152", null));
l.Add(new Hierarchy("44444","child1a",3,"12345", null));
l.Add(new Hierarchy("33333","child1b",3,"12345", null));
l.Add(new Hierarchy("22222","child2a",3,"54321", null));
l.Add(new Hierarchy("22221","child2b",3,"54321", null));
l.Add(new Hierarchy("22002","child2c",3,"54321", null));
l.Add(new Hierarchy("20001","child2a2",4,"22222", null));
l.Add(new Hierarchy("20101","child2b2",4,"22222", null));
l.Add(new Hierarchy("295152","name1",1,null, null)); // <-root node at the bottom of the list
CreateTree(l);
}
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/54747804
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