' 导入命名空间
Imports System.Collections
Imports System.Collections.Specialized
Imports System.Data
Imports System.Data.OleDb
Imports System.Security.Permissions
Imports System.Web

Namespace Samples.AspNet.VB.Controls
 
    ' An extremely simple AccessSiteMapProvider that only supports a
    ' site map node hierarchy one level deep.
    <AspNetHostingPermission(SecurityAction.Demand, Level:=AspNetHostingPermissionLevel.Minimal)> _
    Public Class AccessSiteMapProvider
        Inherits StaticSiteMapProvider

        Private aRootNode As SiteMapNode = Nothing
        Private accessConnection As OleDbConnection = Nothing

        ' This string is case sensitive.
        Private AccessConnectionStringName As String = "accessSiteMapConnectionString"

        ' Implement a default constructor.
        Public Sub New()
        End Sub

        ' Some basic state to help track the initialization state of the provider.
        Private initialized As Boolean = False

        Public Overridable ReadOnly Property IsInitialized() As Boolean
            Get
                Return initialized
            End Get
        End Property

        ' Return the root node of the current site map.
        Public Overrides ReadOnly Property RootNode() As SiteMapNode
            Get
                Return BuildSiteMap()
            End Get
        End Property

        Protected Overrides Function GetRootNodeCore() As SiteMapNode
            Return RootNode
        End Function

        ' Initialize is used to initialize the properties and any state that the
        ' AccessProvider holds, but is not used to build the site map.
        ' The site map is built when the BuildSiteMap method is called.
        Public Overrides Sub Initialize(ByVal name As String, ByVal attributes As NameValueCollection)
            If IsInitialized Then
                Return
            End If
            MyBase.Initialize(name, attributes)

            ' Create and test the connection to the Microsoft Access database.
            ' Retrieve the Value of the Access connection string from the
            ' attributes NameValueCollection.
            Dim connectionString As String = attributes(AccessConnectionStringName)

            If Nothing = connectionString OrElse connectionString.Length = 0 Then
                Throw New Exception("The connection string was not found.")
            Else
                accessConnection = New OleDbConnection(connectionString)
            End If
            initialized = True
        End Sub

        ' SiteMapProvider and StaticSiteMapProvider methods that this derived class must override.
        '
        ' Clean up any collections or other state that an instance of this may hold.
        Protected Overrides Sub Clear()
            SyncLock Me
                aRootNode = Nothing
                MyBase.Clear()
            End SyncLock
        End Sub

        ' Build an in-memory representation from persistent
        ' storage, and return the root node of the site map.
        Public Overrides Function BuildSiteMap() As SiteMapNode

            ' Since the SiteMap class is static, make sure that it is
            ' not modified while the site map is built.
            SyncLock Me

                ' If there is no initialization, this method is being
                ' called out of order.
                If Not IsInitialized Then
                    Throw New Exception("BuildSiteMap called incorrectly.")
                End If

                ' If there is no root node, then there is no site map.
                If aRootNode Is Nothing Then
                    ' Start with a clean slate
                    Clear()

                    ' Select the root node of the site map from Microsoft Access.
                    Dim rootNodeId As Integer = -1

                    If accessConnection.State = ConnectionState.Closed Then
                        accessConnection.Open()
                    End If
                    Dim rootNodeCommand As New OleDbCommand("SELECT nodeid, url, name FROM SiteMap WHERE parentnodeid IS NULL", accessConnection)
                    Dim rootNodeReader As OleDbDataReader = rootNodeCommand.ExecuteReader()

                    If rootNodeReader.HasRows Then
                        rootNodeReader.Read()
                        rootNodeId = rootNodeReader.GetInt32(0)
                        ' Create a SiteMapNode that references the current StaticSiteMapProvider.
                        aRootNode = New SiteMapNode(Me, rootNodeId.ToString(), rootNodeReader.GetString(1), rootNodeReader.GetString(2))
                    Else
                        Return Nothing
                    End If
                    rootNodeReader.Close()
                    ' Select the child nodes of the root node.
                    Dim childNodesCommand As New OleDbCommand("SELECT nodeid, url, name FROM SiteMap WHERE parentnodeid = ?", accessConnection)
                    Dim rootParam As New OleDbParameter("parentid", OleDbType.Integer)
                    rootParam.Value = rootNodeId
                    childNodesCommand.Parameters.Add(rootParam)

                    Dim childNodesReader As OleDbDataReader = childNodesCommand.ExecuteReader()

                    If childNodesReader.HasRows Then

                        Dim childNode As SiteMapNode = Nothing
                        While childNodesReader.Read()
                            childNode = New SiteMapNode(Me, _
                            childNodesReader.GetInt32(0).ToString(), _
                            childNodesReader.GetString(1), _
                            childNodesReader.GetString(2))

                            ' Use the SiteMapNode AddNode method to add
                            ' the SiteMapNode to the ChildNodes collection.
                            AddNode(childNode, aRootNode)
                        End While
                    End If

                    childNodesReader.Close()
                    accessConnection.Close()
                End If
                Return aRootNode
            End SyncLock

        End Function 'BuildSiteMap

    End Class

End Namespace