如何将此 IEnumerable<T> 序列化为 JSON？ (DnnApiController)

Question

问题

我遇到的问题是，在构建后返回“treeNode”时，通过 API 沿线路发送时它不会序列化。对象 [和嵌套元素] 在调试时看起来很棒，但是当浏览器接收到树的数据时，它会转换为空数组（当嵌套更深的子节点时，一些具有正确的长度）。任何帮助表示赞赏，请参阅下面的代码和输出。

跑步：

TreeNode<GenericClass> treeNode = new TreeNode<GenericClass>(new GenericClass() { Title = "Root", URL = null });
GenericClass Google = new GenericClass() { Title = "Google", URL = "https://www.google.com" };
GenericClass Yahoo = new GenericClass() { Title = "Yahoo", URL = "https://www.yahoo.com" };
GenericClass Bing = new GenericClass() { Title = "Bing", URL = "https://www.bing.com" };
treeNode.AddChild(Google);
treeNode.AddChild(Yahoo);
treeNode.AddChild(Bing);
// return treeNode.ToString(); <- Doesnt work
// return treeNode.ToList(); <- Doesnt work
// return JsonConvert.SerializeObject(treeNode); <-Doesnt work
return treeNode;

TreeNode（树/层次结构类）：

public class TreeNode<T> : IEnumerable<TreeNode<T>>
{
    #region Properties
    public T Data { get; set; }
    public TreeNode<T> Parent { get; set; }
    public ICollection<TreeNode<T>> Children { get; set; }
    public Boolean IsRoot
    {
        get { return Parent == null; }
    }
    public Boolean IsLeaf
    {
        get { return Children.Count == 0; }
    }
    public int Level
    {
        get
        {
            if (this.IsRoot)
            {
                return 0;
            }
            return Parent.Level + 1;
        }
    }
    #endregion

    public TreeNode(T data)
    {
        this.Data = data;
        this.Children = new LinkedList<TreeNode<T>>();
        this.ElementsIndex = new LinkedList<TreeNode<T>>();
        this.ElementsIndex.Add(this);
    }

    public TreeNode<T> AddChild(T child)
    {
        TreeNode<T> childNode = new TreeNode<T>(child) { Parent = this };
        this.Children.Add(childNode);
        this.RegisterChildForSearch(childNode);
        return childNode;
    }

    public override string ToString()
    {
        return Data != null ? Data.ToString() : "[data null]";
    }

    private ICollection<TreeNode<T>> ElementsIndex { get; set; }

    private void RegisterChildForSearch(TreeNode<T> node)
    {
        ElementsIndex.Add(node);
        if (Parent != null)
        {
            Parent.RegisterChildForSearch(node);
        } 
    }

    public TreeNode<T> FindTreeNode(Func<TreeNode<T>, bool> predicate)
    {
        return this.ElementsIndex.FirstOrDefault(predicate);
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }

    public IEnumerator<TreeNode<T>> GetEnumerator()
    {
        yield return this;
        foreach (var directChild in this.Children)
        {
            foreach (var anyChild in directChild)
            {
                yield return anyChild;
            }  
        }
    }
}

输出（序列化前）：

输出（序列化后）：

Answer 1

在您的 IEnumerator 实现中，您有一行

yield return this;

这对我来说没有意义。

---

JSON.Net 正在返回

Newtonsoft.Json.JsonSerializationException：自引用循环 检测到

因为它检测到很快 .Net 将返回 StackOverflowException。这个 JSON 看起来如何？

---

超出原始问题的范围，为什么不应该像这样实现您的GetEnumerator 函数？

public IEnumerator<TreeNode<T>> GetEnumerator()
{
    return this.Children.GetEnumerator()
}

乍一看，您的代码似乎在枚举孙子，而不是子孙。

最简单的方法是调试序列化过程。 （如果没有自我引用，这可能需要一段时间。）

Answer 2

*适合我的解决方案

跑步：

TreeNode<GenericClass> treeNode = new TreeNode<GenericClass>(new GenericClass() { Title = "Root", URL = null });
GenericClass Google = new GenericClass() { Title = "Google", URL = "https://www.google.com" };
GenericClass Yahoo = new GenericClass() { Title = "Yahoo", URL = "https://www.yahoo.com" };
GenericClass Bing = new GenericClass() { Title = "Bing", URL = "https://www.bing.com" };
treeNode.AddChild(Google);
treeNode.AddChild(Yahoo);
treeNode.AddChild(Bing);
return JsonConvert.SerializeObject(treeNode, Formatting.Indented, new JsonSerializerSettings() { ReferenceLoopHandling = ReferenceLoopHandling.Ignore });

TreeNode 类：

public class TreeNode<T>
{
    #region Properties
    public T Data { get; set; }
    public TreeNode<T> Parent { get; set; }
    public ICollection<TreeNode<T>> Children { get; set; }
    public Boolean IsRoot
    {
        get { return Parent == null; }
    }
    public Boolean IsLeaf
    {
        get { return Children.Count == 0; }
    }
    public int Level
    {
        get
        {
            if (this.IsRoot)
            {
                return 0;
            }
            return Parent.Level + 1;
        }
    }
    #endregion

    public TreeNode(T data)
    {
        this.Data = data;
        this.Children = new LinkedList<TreeNode<T>>();
        this.ElementsIndex = new LinkedList<TreeNode<T>>();
        this.ElementsIndex.Add(this);
    }

    public TreeNode<T> AddChild(T child)
    {
        TreeNode<T> childNode = new TreeNode<T>(child) { Parent = this };
        this.Children.Add(childNode);
        this.RegisterChildForSearch(childNode);
        return childNode;
    }

    public override string ToString()
    {
        return Data != null ? Data.ToString() : "[data null]";
    }

    private ICollection<TreeNode<T>> ElementsIndex { get; set; }

    private void RegisterChildForSearch(TreeNode<T> node)
    {
        ElementsIndex.Add(node);
        if (Parent != null)
        {
            Parent.RegisterChildForSearch(node);
        } 
    }

    public TreeNode<T> FindTreeNode(Func<TreeNode<T>, bool> predicate)
    {
        return this.ElementsIndex.FirstOrDefault(predicate);
    }
}

返回：

{
  "Data": {
    "Title": "Root",
    "URL": null
  },
  "Parent": null,
  "Children": [
    {
      "Data": {
        "Title": "Google",
        "URL": "https://www.google.com"
      },
      "Children": [],
      "IsRoot": false,
      "IsLeaf": true,
      "Level": 1
    },
    {
      "Data": {
        "Title": "Yahoo",
        "URL": "https://www.yahoo.com"
      },
      "Children": [],
      "IsRoot": false,
      "IsLeaf": true,
      "Level": 1
    },
    {
      "Data": {
        "Title": "Bing",
        "URL": "https://www.bing.com"
      },
      "Children": [],
      "IsRoot": false,
      "IsLeaf": true,
      "Level": 1
    }
  ],
  "IsRoot": true,
  "IsLeaf": false,
  "Level": 0
}