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.

        <Grid> 
            <Grid.Resources> 
                <telerik:HierarchicalDataTemplate x:Key="treeViewTemplate" ItemsSource="{Binding Children}"> 
                    <TextBlock Text="{Binding Title}" /> 
                </telerik: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.

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; 
            } 
        } 
    } 
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.

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 whenever the expander is clicked. For demonstration purposes we will load fixed number of business data every time the getter is triggered and the children field is not yet instantiated.

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; 
    } 
} 
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.

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('\'); 
} 
    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 Rad Tree View How To Expand And Select Item

See Also

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