Bind RadTreeView to Hierarchical Data from WCF Service and Use Load on Demand

The purpose of this tutorial is to show you how to populate RadTreeView with hierarchical data loaded from WCF service.

Here is a simple treeview declaration:

<UserControl.Resources> 
 
    <example:HierarchicalDataSource x:Key="Source" /> 
 
    <HierarchicalDataTemplate x:Key="NodeTemplate" 
        ItemsSource="{Binding Children}"> 
        <TextBlock Text="{Binding Text}"/> 
    </HierarchicalDataTemplate> 
 
</UserControl.Resources> 
 
<Grid x:Name="LayoutRoot" Background="White"> 
 
    <telerik:RadTreeView x:Name="radTreeView" Margin="8" 
        ItemsSource="{Binding Source={StaticResource Source}}" 
        ItemTemplate="{StaticResource NodeTemplate}"/> 
 
</Grid> 

The web service will return an observable collection with objects of type TableItem. Here is the TableItem structure:

public class TableItem 
{ 
    public TableItem() 
    { 
        this.Children = new List<TableItem>(); 
    } 
    public int Id 
    { 
        get; 
        set; 
    } 
    public int ParentId 
    { 
        get; 
        set; 
    } 
    public string Text 
    { 
        get; 
        set; 
    } 
    public List<TableItem> Children 
    { 
        get; 
        set; 
    } 
} 
Public Class TableItem 
    Public Sub New() 
        Me.Children = New List(Of TableItem)() 
    End Sub 
 
Private _Id As Integer 
    Public Property Id() As Integer 
        Get 
            Return _Id 
        End Get 
        Set(ByVal value As Integer) 
            _Id = value 
        End Set 
    End Property 
 
Private _ParentId As Integer 
    Public Property ParentId() As Integer 
        Get 
            Return _ParentId 
        End Get 
        Set(ByVal value As Integer) 
            _ParentId = value 
        End Set 
    End Property 
 
Private _Text As String 
    Public Property Text() As String 
        Get 
            Return _Text 
        End Get 
        Set(ByVal value As String) 
            _Text = value 
        End Set 
    End Property 
 
Private _Children As List(Of TableItem) 
    Public Property Children() As List(Of TableItem) 
        Get 
            Return _Children 
        End Get 
        Set(ByVal value As List(Of TableItem)) 
            _Children = value 
        End Set 
    End Property 
End Class 

Now that you have the basis set up, it's time to go on. First you should create your data source object. Add a new class named HierarchicalDataSource which derives from ObservableCollection of TableItem.

public class HierarchicalDataSource : ObservableCollection<TableItem> 
{ 
    public HierarchicalDataSource() 
    { 
    } 
} 
Public Class HierarchicalDataSource 
    Inherits ObservableCollection(Of TableItem) 
    Public Sub New() 
    End Sub 
End Class 

Next, you need to add a reference to the WCF service and load the data. You also need a list that holds all items that come from the web service result.

public class HierarchicalDataSource : ObservableCollection<TableItem> 
{ 
    // This list holds all the items that come from the web service result 
    private List<TableItem> unsortedList = new List<TableItem>(); 
    public HierarchicalDataSource() 
    { 
        SampleWcfServiceClient serviceClient = new SampleWcfServiceClient(); 
        serviceClient.LoadHierarchicalDataCompleted += new EventHandler<LoadHierarchicalDataCompletedEventArgs>( serviceClient_LoadHierarchicalDataCompleted ); 
        serviceClient.LoadHierarchicalDataAsync(); 
    } 
    private void serviceClient_LoadHierarchicalDataCompleted( object sender, LoadHierarchicalDataCompletedEventArgs e ) 
    { 
        // transfer all the items from the result to the unsorted list 
        foreach ( TableItem item in e.Result ) 
        { 
            TableItem genericItem = new TableItem() 
            { 
                Text = item.Text, 
                Id = item.Id, 
                ParentId = item.ParentId 
            }; 
            this.unsortedList.Add( genericItem ); 
        } 
        // Get all the first level nodes. 
        var rootNodes = this.unsortedList.Where( x => x.ParentId == 0 ); 
        // Foreach root node, get all its children and add the node to the HierarchicalDataSource. 
        // see below how the FindChildren method works 
        foreach ( TableItem node in rootNodes ) 
        { 
            this.FindChildren( node ); 
            this.Add( node ); 
        } 
    } 
} 
Public Class HierarchicalDataSource 
    Inherits ObservableCollection(Of TableItem) 
    ' This list holds all the items that come from the web service result' 
    Private unsortedList As New List(Of TableItem)() 
 
    Public Sub New() 
        Dim serviceClient As New SampleWcfServiceClient() 
        AddHandler serviceClient.LoadHierarchicalDataCompleted, AddressOf serviceClient_LoadHierarchicalDataCompleted 
        serviceClient.LoadHierarchicalDataAsync() 
    End Sub 
 
    Private Sub serviceClient_LoadHierarchicalDataCompleted(ByVal sender As Object, ByVal e As LoadHierarchicalDataCompletedEventArgs) 
        ' transfer all the items from the result to the unsorted list' 
        For Each item As TableItem In e.Result 
            Dim genericItem As New TableItem() 
            Me.unsortedList.Add(genericItem) 
        Next 
 
        ' Get all the first level nodes.' 
        Dim rootNodes = Me.unsortedList.Where(Function(x) x.ParentId = 0) 
 
        ' Foreach root node, get all its children and add the node to the HierarchicalDataSource.' 
        ' see below how the FindChildren method works' 
        For Each node As TableItem In rootNodes 
            Me.FindChildren(node) 
            Me.Add(node) 
        Next 
    End Sub 
End Class 

Add the FindChildren() method to the HierarchicalDataSource file. It will find all child nodes by a given item.

private void FindChildren( TableItem item ) 
{ 
    // find all the children of the item 
    var children = unsortedList.Where( x => x.ParentId == item.Id && x.Id != item.Id ); 
    // add the child to the item's children collection and call the FindChildren recursively, in case the child has children 
    foreach ( TableItem child in children ) 
    { 
        // By not calling iteratively FindChildren() here we prevent 
        // the automatic loading of all items in the data 
        // source and load only the next level in the hierarchy 
        item.Children.Add( child ); 
    } 
} 
Private Sub FindChildren(ByVal item As TableItem) 
    ' find all the children of the item' 
    Dim children = unsortedList.Where(Function(x) x.ParentId = item.Id AndAlso x.Id <> item.Id) 
 
    ' add the child to the items children collection and call the FindChildren recursively, in case the child has children' 
    For Each child As TableItem In children 
        ' By not calling iteratively FindChildren() here we prevent' 
        ' the automatic loading of all items in the data' 
        ' source and load only the next level in the hierarchy' 
        item.Children.Add(child) 
    Next 
End Sub 

Add a public method named LoadItemChildren(). This method visits all current items and adds their direct children to the data source, if there are any.

public void LoadItemChildren( TableItem item ) 
{ 
    foreach ( TableItem i in item.Children ) 
    { 
        FindChildren( i ); 
    } 
} 
Public Sub LoadItemChildren(ByVal item As TableItem) 
    For Each i As TableItem In item.Children 
        FindChildren(i) 
    Next 
End Sub 

Finally add an event handler in your treeview declaration for the Expanded event.

<telerik:RadTreeView x:Name="radTreeView" Margin="8" 
    Expanded="radTreeView_Expanded" 
    ItemsSource="{Binding Source={StaticResource Source}}" 
    ItemTemplate="{StaticResource NodeTemplate}"/> 
Switch to the code-behind and the following code to handle the event.

private void radTreeView_Expanded( object sender, Telerik.Windows.RadRoutedEventArgs e ) 
{ 
    Telerik.Windows.Controls.RadTreeView tree = sender as Telerik.Windows.Controls.RadTreeView; 
    RadTreeViewItem item = e.OriginalSource as RadTreeViewItem; 
    if ( ( tree != null ) && ( item != null ) ) 
    { 
        // Load the next level from the data hierarchy 
        HierarchicalDataSource source = this.Resources[ "Source" ] as HierarchicalDataSource; 
        TableItem ti = item.DataContext as TableItem; 
        if ( ( ti != null ) && ( source != null ) ) 
        { 
            source.LoadItemChildren( ti ); 
        } 
    } 
} 
Private Sub radTreeView_Expanded(ByVal sender As Object, ByVal e As Telerik.Windows.RadRoutedEventArgs) 
    Dim tree As Telerik.Windows.Controls.RadTreeView = TryCast(sender, Telerik.Windows.Controls.RadTreeView) 
    Dim item As RadTreeViewItem = TryCast(e.OriginalSource, RadTreeViewItem) 
    If (tree IsNot Nothing) AndAlso (item IsNot Nothing) Then 
        ' Load the next level from the data hierarchy' 
        Dim source As HierarchicalDataSource = TryCast(Me.Resources("Source"), HierarchicalDataSource) 
        Dim ti As TableItem = TryCast(item.DataContext, TableItem) 
        If (ti IsNot Nothing) AndAlso (source IsNot Nothing) Then 
            source.LoadItemChildren(ti) 
        End If 
    End If 
End Sub 

Here, you first get references to the treeview and the item that was expanded. Then, you get a reference to the hierarchical data source and call its LoadItemChildren() method and pass the value of the expanded item. What the method does is fetching the children of that data item via the web service and adding them as children of the treeview.

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