Expand and Select Item with Load on Demand Enabled RadTreeView

This tutorial will demonstrate you how to expand and select an item when the RadTreeView is in load on demand mode (IsLoadOnDemandEnabled property is set to True).

For the purpose of this topic a RadTreeView which is data bound to a business object will be used. The next several code snippets show you the RadTreeView declaration and the business object structure.

XAML

	        <Grid>
	            <Grid.Resources>
	                <HierarchicalDataTemplate x:Key="treeViewTemplate" ItemsSource="{Binding Children}">
	                    <TextBlock Text="{Binding Title}" />
	                </HierarchicalDataTemplate>
	            </Grid.Resources>
	            <Grid.ColumnDefinitions>
	                <ColumnDefinition Width="Auto" />
	                <ColumnDefinition Width="300" />
	            </Grid.ColumnDefinitions>
	
	            <telerik:RadTreeView x:Name="treeView"
	                             Margin="8"
	                             HorizontalAlignment="Stretch"
	                             IsLoadOnDemandEnabled="True"
	                             IsVirtualizing="True"
	                             ItemTemplate="{StaticResource treeViewTemplate}"
	                             telerik:TextSearch.TextPath="Title" />
	
	            <StackPanel Grid.Column="1"
	                    Width="300"
	                    HorizontalAlignment="Right"
	                    VerticalAlignment="Top">
	                <Button Click="Button_Click_1" Content="Bring Item" />
	                <TextBox x:Name="userInput" />
	            </StackPanel>
	        </Grid>

The data source for the radtreeview will be consisted of DataItems, only.

C#

	public class DataItem : ViewModelBase
	    {
	        private string title;
	        private List<DataItem> children;
	
	        public String Title
	        {
	            get
	            {
	                return this.title;
	            }
	            set
	            {
	                if (this.title != value)
	                {
	                    this.title = value;
	                    this.OnPropertyChanged("Title");
	                }
	            }
	        }
	
	        public List<DataItem> Children
	        {
	            get
	            {
	                return this.children;
	            }
	        }
	    }

VB.NET

	Public Class DataItem
	        Inherits ViewModelBase
	        Private m_title As String
	        Private m_children As List(Of DataItem)
	
	        Public Property Title() As [String]
	            Get
	                Return Me.m_title
	            End Get
	            Set(value As [String])
	                If Me.m_title <> value Then
	                    Me.m_title = value
	                    Me.OnPropertyChanged("Title")
	                End If
	            End Set
	        End Property
	
	        Public ReadOnly Property Children() As List(Of DataItem)
	            Get
	                Return Me.m_children
	            End Get
	        End Property
	    End Class

Set a DataItem instance to the ItemsSource property of the RadTreeView and create some simple data like in the code snippet below.

C#

	this.treeView.ItemsSource = Enumerable.Range(1, 10).Select(i => new DataItem()
	{
	    Title = string.Format("Item {0}", i)
	}).ToList();

The actual loading on demand of the business items can be implemented in the getter of the Children property of the DataItem class. The LoadOnDemand feature of the RadTreeView control is used to visualize the expander icon in the front of each RadTreeViewItem. We do not use the built-in LoadOnDemand event to load the business items into the control. Instead, the HierarchicalDataTemplate will trigger the getter of its ItemsSource property on load. For demonstration purposes, we will load a fixed number of business data every time the getter is triggered and the children field is not yet instantiated.

C#

	public List<DataItem> Children
	{
	    get
	    {
	        if (this.children == null)
	        {
	            this.children = new List<DataItem>();
	            for (int i = 0; i < 5; i++)
	            {
	                DataItem item = new DataItem() { Title = string.Format("{0}.{1}", this.Title, i) };
	                this.children.Add(item);
	            }
	        }
	        return this.children;
	    }
	}

VB.NET

	Public ReadOnly Property Children() As List(Of DataItem)
	        Get
	            If Me.children Is Nothing Then
	                Me.children = New List(Of DataItem)()
	                For i As Integer = 0 To 4
					Dim item As New DataItem() With { _
						Key .Title = String.Format("{0}.{1}", Me.Title, i) _
					}
	                    Me.children.Add(item)
	                Next
	            End If
	            Return Me.children
	        End Get
	    End Property

The next step is to implement the custom logic for creating the path in order to use the BringPathIntoView() method.

C#

	private void Button_Click_1(object sender, RoutedEventArgs e)
	{
	    string[] headerAndIndexes = this.userInput.Text.Split(' ');
	    string[] indexes = headerAndIndexes.LastOrDefault().Split('.');
	    bool areIndexesValid = false;
	    int i;
	
	    if (headerAndIndexes != null && indexes != null)
	    {
	        foreach (string index in indexes)
	        {
	            areIndexesValid = int.TryParse(index, out i);
	        }
	
	        if (headerAndIndexes.FirstOrDefault().Contains("Item") && areIndexesValid)
	        {
	            RadTreeViewItem item = this.treeView.GetItemByPath(this.GenetatePath(this.userInput.Text));
	            if (item != null)
	            {
	                item.IsSelected = true;
	                item.IsExpanded = true;
	            }
	        }
	    }
	}
	  
	private string GenetatePath(string itemToExpand)
	{
	    string path = string.Empty;
	    string buffer;
	    string[] header = itemToExpand.Split(' ');
	    string[] indexes = header.LastOrDefault().Split('.');
	
	    header[0] = string.Format("{0} {1}", header[0], indexes[0]);
	    path = string.Format("{0}\\", header[0]);
	
	    for (int i = 1; i < indexes.Length; i++)
	    {
	        buffer = string.Format("{0}.{1}", header[0], indexes[i]);
	        header[0] = buffer;
	        path += string.Format("{0}\\", buffer);
	    }
	    return path.TrimEnd('\\');
	}

VB.NET

	
	    Private Sub Button_Click_1(sender As Object, e As RoutedEventArgs)
	        Dim headerAndIndexes As String() = Me.userInput.Text.Split(" "c)
	        Dim indexes As String() = headerAndIndexes.LastOrDefault().Split("."c)
	        Dim areIndexesValid As Boolean = False
	        Dim i As Integer
	
	        If headerAndIndexes IsNot Nothing AndAlso indexes IsNot Nothing Then
	            For Each index As String In indexes
	                areIndexesValid = Integer.TryParse(index, i)
	            Next
	
	            If headerAndIndexes.FirstOrDefault().Contains("Item") AndAlso areIndexesValid Then
	                Dim item As RadTreeViewItem = Me.treeView.GetItemByPath(Me.GenetatePath(Me.userInput.Text))
	                If item IsNot Nothing Then
	                    item.IsSelected = True
	                    item.IsExpanded = True
	                End If
	            End If
	        End If
	    End Sub
	
	    Private Function GenetatePath(itemToExpand As String) As String
	        Dim path As String = String.Empty
	        Dim buffer As String
	        Dim header As String() = itemToExpand.Split(" "c)
	        Dim indexes As String() = header.LastOrDefault().Split("."c)
	
	        header(0) = String.Format("{0} {1}", header(0), indexes(0))
	        path = String.Format("{0}\", header(0))
	
	        For i As Integer = 1 To indexes.Length - 1
	            buffer = String.Format("{0}.{1}", header(0), indexes(i))
	            header(0) = buffer
	            path += String.Format("{0}\", buffer)
	        Next
	        Return path.TrimEnd("\"c)
	    End Function

The final result after bringing Item 2.3.1.4 should look like this

See Also

• Get Item by Path
• Selection
• Get Previous, Next, Parent and Sibling Node of a Specific TreeView Item