面试题：Visual Basic动态类型与ExpandoObject在复杂数据结构中的应用

Question

假设你需要使用Visual Basic的动态类型和ExpandoObject来构建一个类似树状的数据结构，每个节点都可以动态添加属性，并且节点之间有父子关系。请描述实现思路并给出核心代码片段，说明如何遍历这个树状结构并获取特定节点的所有动态属性。

Answer 1

实现思路

1. 使用ExpandoObject创建动态节点：ExpandoObject允许在运行时动态添加属性，符合每个节点可动态添加属性的要求。
2. 建立父子关系：在每个ExpandoObject中添加一个属性来存储子节点列表，以构建树状结构。
3. 遍历树状结构：可以使用递归或迭代的方式遍历树，找到特定节点，并获取其所有动态属性。

核心代码片段

Imports System.Dynamic

' 创建树节点
Public Function CreateTreeNode() As ExpandoObject
    Dim node As New ExpandoObject()
    Dim childrenList As New List(Of ExpandoObject)()
    CType(node, IDictionary(Of String, Object)).Add("Children", childrenList)
    Return node
End Function

' 添加子节点
Public Sub AddChild(parent As ExpandoObject, child As ExpandoObject)
    Dim children = CType(CType(parent, IDictionary(Of String, Object))("Children"), List(Of ExpandoObject))
    children.Add(child)
End Sub

' 动态添加属性到节点
Public Sub AddDynamicProperty(node As ExpandoObject, propertyName As String, propertyValue As Object)
    CType(node, IDictionary(Of String, Object)).Add(propertyName, propertyValue)
End Sub

' 递归遍历树并获取特定节点的所有动态属性
Public Function GetPropertiesOfNode(root As ExpandoObject, targetNode As ExpandoObject) As Dictionary(Of String, Object)
    Dim result As New Dictionary(Of String, Object)()
    If root Is targetNode Then
        For Each kvp In CType(root, IDictionary(Of String, Object))
            If kvp.Key <> "Children" Then
                result.Add(kvp.Key, kvp.Value)
            End If
        Next
        Return result
    End If
    Dim children = CType(CType(root, IDictionary(Of String, Object))("Children"), List(Of ExpandoObject))
    For Each child In children
        Dim childResult = GetPropertiesOfNode(child, targetNode)
        If childResult.Count > 0 Then
            Return childResult
        End If
    Next
    Return result
End Function

示例使用

Module Module1
    Sub Main()
        ' 创建根节点
        Dim root = CreateTreeNode()
        AddDynamicProperty(root, "Name", "RootNode")

        ' 创建子节点
        Dim child1 = CreateTreeNode()
        AddDynamicProperty(child1, "Name", "Child1")
        AddChild(root, child1)

        Dim child2 = CreateTreeNode()
        AddDynamicProperty(child2, "Name", "Child2")
        AddChild(root, child2)

        ' 获取Child1的所有动态属性
        Dim properties = GetPropertiesOfNode(root, child1)
        For Each kvp In properties
            Console.WriteLine($"{kvp.Key}: {kvp.Value}")
        Next
    End Sub
End Module

遍历和获取特定节点属性说明

1. 遍历：GetPropertiesOfNode方法采用递归方式遍历树。从根节点开始，如果当前节点是目标节点，则将其除“Children”之外的所有属性添加到结果字典中并返回。否则，递归地在子节点中查找目标节点。
2. 获取属性：找到目标节点后，通过IDictionary(Of String, Object)接口遍历节点的属性，将非“Children”属性添加到结果字典，以此获取特定节点的所有动态属性。