c# - 在树结构上实现 IEnumerable

Question

基于这些人的工作:

• http://dvanderboom.wordpress.com/2008/03/15/treet-implementing-a-non-binary-tree-in-c/
• http://www.matthidinger.com/archive/2009/02/08/asp.net-mvc-recursive-treeview-helper.aspx

我正在尝试实现一个 TreeView 助手，它可以这样使用:

<%= Html.TreeView("records", 
                  Library.Instance.Records, 
                  r => r.Children, 
                  r => r.ID) %>

树结构定义如下:

public class Tree<T> : TreeNode<T> where T : TreeNode<T>
{ }


public class TreeNode<T> : IDisposable where T : TreeNode<T>
{
    public T Parent { get; set; }
    public TreeNodeList<T> Children { get; set; }
}


public class TreeNodeList<T> : List<TreeNode<T>> where T : TreeNode<T>
{
    public T Parent;

    public T Add(T node)
    {
        base.Add(node);
        node.Parent = (T)Parent;
        return node;
    }

    public void Remove(T node)
    {
        if (node != null)
            node.Parent = null;
        base.Remove(node);
    }
}

TreeView 助手有这个签名:

public static string TreeView<T>(this HtmlHelper htmlHelper, string treeId,
   IEnumerable<T> rootItems, Func<T, IEnumerable<T>> childrenProperty, 
   Func<T, string> itemContent, bool includeJavascript, string emptyContent)
{
    ...
}   

因此，我需要我的树结构来实现 IEnumerable，这样我就可以将它与 TreeView 助手一起使用，这就引出了一个问题:在这种情况下，我应该在哪里以及如何实现 IEnumerable？

Answer 1

我不完全理解您的树结构的确切细节，但这是一个简单的实现，它采用通用节点树并将其递归呈现为 html 列表。

public static string TreeView<T>(IEnumerable<T> rootItems,
                                 Func<T, IEnumerable<T>> childrenProperty,
                                 Func<T, string> itemContent)
{
    if (rootItems == null || !rootItems.Any()) return null;

    var builder = new StringBuilder();
    builder.AppendLine("<ul>");

    foreach (var item in rootItems)
    {
        builder.Append("  <li>").Append(itemContent(item)).AppendLine("</li>");
        var childContent = htmlHelper.TreeView(treeId,
                                               childrenProperty(item),
                                               childrenProperty,
                                               itemContent);

        if (childContent != null)
        {
            var indented = childContent.Replace(Environment.NewLine,
                                                Environment.NewLine + "  ");
            builder.Append("  ").AppendLine(indented);
        }
    }

    builder.Append("</ul>");
    return builder.ToString();
}

我使用的节点类相对简单，只有两个属性。

public class Node<T>
{
    public Node(T data)
    {
        Data = data;
        Children = new List<Node<T>>();
    }

    public T Data { get; private set; }
    public ICollection<Node<T>> Children { get; private set; }
}

下面是一些将树输出到控制台的测试代码。

var Records = new[] {
    new Node<string>("one") {
        Children = {
            new Node<string>("one-one") {
                Children = {
                    new Node<string>("one-one-one"),
                    new Node<string>("one-one-two"),
                    new Node<string>("one-one-three")
                }
            },
            new Node<string>("one-two"),
            new Node<string>("one-three")
        }
    },
    new Node<string>("two"),
    new Node<string>("three")
};
Console.WriteLine(TreeView(Records,
                           r => r.Children,
                           r => r.Data));

下面是上述代码的结果。

<ul>
  <li>one</li>
  <ul>
    <li>one-one</li>
    <ul>
      <li>one-one-one</li>
      <li>one-one-two</li>
      <li>one-one-three</li>
    </ul>
    <li>one-two</li>
    <li>one-three</li>
  </ul>
  <li>two</li>
  <li>three</li>
</ul>