Use the Node Iterator

• Dec 17, 2020
• 3 minutes to read

The ASPxTreeList introduces the Node Iterator, which allows you to traverse through the nodes and avoid writing recursive code.

To use the Node Iterator you should create a new instance of the TreeListNodeIterator object. A start node is specified within the constructor.

C#

TreeListNodeIterator iterator = new TreeListNodeIterator(startNode);

VB.NET

Dim iterator As TreeListNodeIterator = New TreeListNodeIterator(startNode)

To start traversing from the root node, pass the ASPxTreeList.RootNode as a parameter.

C#

TreeListNodeIterator iterator = new TreeListNodeIterator(treeList.RootNode);

VB.NET

Dim iterator As TreeListNodeIterator = New TreeListNodeIterator(treeList.RootNode)

You can also use the ASPxTreeList.CreateNodeIterator method to create the Nodes Iterator.

C#

TreeListNodeIterator iterator = treeList.CreateNodeIterator(startNode);

// Starts traversing from the root node
TreeListNodeIterator iteratorFromRoot = treeList.CreateNodeIterator();

VB.NET

Dim iterator As TreeListNodeIterator = treeList.CreateNodeIterator(startNode)

' Starts traversing from the root node
Dim iteratorFromRoot As TreeListNodeIterator = treeList.CreateNodeIterator()

The current node is returned by the TreeListNodeIterator.Current property. To obtain the next node, use the TreeListNodeIterator.GetNext method.

To return the Node Iterator to its default state, call the TreeListNodeIterator.Reset method.

Example

This example shows how to collect the key values of all parent nodes displayed within the ASPxTreeList. The TreeListNodeIterator object is used to traverse through the nodes.

ASPX

<dx:ASPxTreeList ID="treeList" runat="server" Width="100%" KeyFieldName="ID" ParentFieldName="Parent_ID"
    AutoGenerateColumns="False" OnDataBound="treeList_DataBound">
    <Columns>
        <dx:TreeListDataColumn FieldName="Title" VisibleIndex="0" />
    </Columns>
</dx:ASPxTreeList>

C#

using DevExpress.Web.ASPxTreeList;
using System;
using System.Collections.Generic;
using System.Data;

protected void Page_Load(object sender, EventArgs e) {
    DataTable dt = new DataTable();
    dt.Columns.Add("ID");
    dt.Columns.Add("Parent_ID");
    dt.Columns.Add("Title");

    dt.Rows.Add(dt.NewRow());
    dt.Rows[dt.Rows.Count - 1]["ID"] = 1;
    dt.Rows[dt.Rows.Count - 1]["Parent_ID"] = null;
    dt.Rows[dt.Rows.Count - 1]["Title"] = "One";

    dt.Rows.Add(dt.NewRow());
    dt.Rows[dt.Rows.Count - 1]["ID"] = 4;
    dt.Rows[dt.Rows.Count - 1]["Parent_ID"] = 1;
    dt.Rows[dt.Rows.Count - 1]["Title"] = "One A";

    dt.Rows.Add(dt.NewRow());
    dt.Rows[dt.Rows.Count - 1]["ID"] = 5;
    dt.Rows[dt.Rows.Count - 1]["Parent_ID"] = 1;
    dt.Rows[dt.Rows.Count - 1]["Title"] = "One B";

    treeList.DataSource = dt;
    treeList.DataBind();
}

protected void treeList_DataBound(object sender, EventArgs e) {
    ASPxTreeList list = sender as ASPxTreeList;
    ProcessNodes(list.Nodes[0]);
}
List<string> nodeKeys;
void ProcessNodes(TreeListNode startNode) {
    if (startNode == null) return;
    TreeListNodeIterator iterator = new TreeListNodeIterator(startNode);
    nodeKeys = new List<string>();
    while (iterator.Current != null) {
        GetParentNodeKey(iterator.Current);
        iterator.GetNext();
    }
}

private void GetParentNodeKey(TreeListNode node) {
    if (node != treeList.RootNode && node.HasChildren)
        nodeKeys.Add(node.Key);
}

VB.NET

Imports DevExpress.Web.ASPxTreeList
Imports System
Imports System.Collections.Generic
Imports System.Data

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
    Dim dt As System.Data.DataTable = New System.Data.DataTable()
    dt.Columns.Add("ID")
    dt.Columns.Add("Parent_ID")
    dt.Columns.Add("Title")
    dt.Rows.Add(dt.NewRow())
    dt.Rows(dt.Rows.Count - 1)("ID") = 1
    dt.Rows(dt.Rows.Count - 1)("Parent_ID") = Nothing
    dt.Rows(dt.Rows.Count - 1)("Title") = "One"
    dt.Rows.Add(dt.NewRow())
    dt.Rows(dt.Rows.Count - 1)("ID") = 4
    dt.Rows(dt.Rows.Count - 1)("Parent_ID") = 1
    dt.Rows(dt.Rows.Count - 1)("Title") = "One A"
    dt.Rows.Add(dt.NewRow())
    dt.Rows(dt.Rows.Count - 1)("ID") = 5
    dt.Rows(dt.Rows.Count - 1)("Parent_ID") = 1
    dt.Rows(dt.Rows.Count - 1)("Title") = "One B"
    treeList.DataSource = dt
    treeList.DataBind()
End Sub

Protected Sub treeList_DataBound(ByVal sender As Object, ByVal e As EventArgs)
    Dim list As ASPxTreeList = TryCast(sender, ASPxTreeList)
    ProcessNodes(list.Nodes(0))
End Sub

Private nodeKeys As List(Of String)

Private Sub ProcessNodes(ByVal startNode As TreeListNode)
    If startNode Is Nothing Then Return
    Dim iterator As TreeListNodeIterator = New TreeListNodeIterator(startNode)
    nodeKeys = New List(Of String)()

    While iterator.Current IsNot Nothing
        GetParentNodeKey(iterator.Current)
        iterator.GetNext()
    End While
End Sub

Private Sub GetParentNodeKey(ByVal node As TreeListNode)
    If Not node Is treeList.RootNode AndAlso node.HasChildren Then
        nodeKeys.Add(node.Key)
    End If
End Sub