Working with ItemPrepared Event

The purpose of this tutorial is to show you how to work with the RadTreeView's ItemPrepared event. This event occurs when a child RadTreeViewItem has been prepared and is now ready for use. The main goal of this event is to perform binding of RadTreeViewItem properties to the data objects.

The example shown in this tutorial will demonstrate you how to bind the check state of individual treeview items to a ToggleState property of a class.

In few words, the approaches that you should follow are:

• Create a sample data source

  For the purpose of this example the following business objects will be used:

      public class DataItem 
      { 
          public DataItem() 
          { 
              this.Items = new List<DataItem>(); 
          } 
   
          public string Name 
          { 
              get; 
              set; 
          } 
   
          public System.Windows.Automation.ToggleState CheckState 
          { 
              get; 
              set; 
          } 
   
          public List<DataItem> Items 
          { 
              get; 
              set; 
          } 
      } 
  

      Public Class DataItem 
          Public Sub New() 
              Me.Items = New List(Of DataItem)() 
          End Sub 
   
      Private _Name As String 
          Public Property Name() As String 
              Get 
                  Return _Name 
              End Get 
              Set(ByVal value As String) 
                  _Name = value 
              End Set 
          End Property 
   
      Private _CheckState As System.Windows.Automation.ToggleState 
          Public Property CheckState() As System.Windows.Automation.ToggleState 
              Get 
                  Return _CheckState 
              End Get 
              Set(ByVal value As System.Windows.Automation.ToggleState) 
                  _CheckState = value 
              End Set 
          End Property 
   
      Private _Items As List(Of DataItem) 
          Public Property Items() As List(Of DataItem) 
              Get 
                  Return _Items 
              End Get 
              Set(ByVal value As List(Of DataItem)) 
                  _Items = value 
              End Set 
          End Property 
      End Class 
  

  The CheckState property of the DataItem class will be bound to the CheckState property of the RadTreeViewItem.

      public class RawDataSource : List<DataItem> 
      { 
          public RawDataSource() 
          { 
              Random rand = new Random( ( int )DateTime.Now.Ticks ); 
              for ( int i = 1; i < 11; i++ ) 
              { 
                  DataItem item = new DataItem() 
                  { 
                      Name = String.Format( "Item {0}", i.ToString() ), 
                      CheckState = GetToggleState( rand.Next( 0, 3 ) ) 
                  }; 
                  for ( int j = 1; j < 11; j++ ) 
                  { 
                      DataItem subItem = new DataItem() 
                      { 
                          Name = String.Format( "Item {0}.{1}", i.ToString(), j.ToString() ), 
                          CheckState = GetToggleState( rand.Next( 0, 3 ) ) 
                      }; 
                      item.Items.Add( subItem ); 
                  } 
                  this.Add( item ); 
              } 
          } 
   
          private System.Windows.Automation.ToggleState GetToggleState( int code ) 
          { 
              switch ( code ) 
              { 
                  case 0: 
                      return System.Windows.Automation.ToggleState.Off; 
                  case 1: 
                      return System.Windows.Automation.ToggleState.On; 
                  case 2: 
                      return System.Windows.Automation.ToggleState.Indeterminate; 
                  default: 
                      return System.Windows.Automation.ToggleState.Off; 
              } 
          } 
      } 
  

      Public Class RawDataSource 
          Inherits List(Of DataItem) 
          Public Sub New() 
              Dim rand As New Random(CInt(DateTime.Now.Ticks)) 
              For i As Integer = 1 To 10 
                  Dim item As New DataItem() 
   
                  For j As Integer = 1 To 10 
                      Dim subItem As New DataItem() 
                      item.Items.Add(subItem) 
                  Next 
   
                  Me.Add(item) 
              Next 
          End Sub 
   
          Private Function GetToggleState(ByVal code As Integer) As System.Windows.Automation.ToggleState 
              Select Case code 
                  Case 0 
                      Return System.Windows.Automation.ToggleState.Off 
                  Case 1 
                      Return System.Windows.Automation.ToggleState.[On] 
                  Case 2 
                      Return System.Windows.Automation.ToggleState.Indeterminate 
                  Case Else 
                      Return System.Windows.Automation.ToggleState.Off 
              End Select 
          End Function 
      End Class 
  

  The RawDataSource does nothing special, except for initializing the sample data for the RadTreeView. This is the data source for the treeview.

• Add a new RadTreeView declaration. Enable the following properties:

  • IsOptionElementsEnabled
  • IsTriStateMode

      <telerik:RadTreeView x:Name="radTreeView" IsOptionElementsEnabled="True" IsTriStateMode="True"/> 
  

• Declare a RawDataSource object as a resource in your XAML and set the RadTreeView's ItemsSource property.

      <UserControl.Resources> 
          <example:RawDataSource x:Key="DataSource"/> 
      </UserControl.Resources> 
      .... 
      <telerik:RadTreeView x:Name="radTreeView"  
                           IsOptionElementsEnabled="True"  
                           IsTriStateMode="True"  
                           ItemsSource="{StaticResource DataSource}"/> 
  

• Declare a new HierarchicalDataTemplate in your XAML resources and set the RadTreeView's ItemTemplate property.

      <UserControl.Resources> 
          <example:RawDataSource x:Key="DataSource"/> 
          <telerik:HierarchicalDataTemplate x:Key="ItemTemplate" ItemsSource="{Binding Items}"> 
              <StackPanel Orientation="Horizontal"> 
                  <TextBlock Text="{Binding Name}" /> 
              </StackPanel> 
          </telerik:HierarchicalDataTemplate> 
      </UserControl.Resources> 
      .... 
      <telerik:RadTreeView x:Name="radTreeView"  
                           IsOptionElementsEnabled="True" 
                           IsTriStateMode="True" 
                           ItemsSource="{StaticResource DataSource}"  
                           ItemTemplate="{StaticResource ItemTemplate}"/> 
  

• The final and most important step is to attach to the ItemPrepared event of the RadTreeView.

      <telerik:RadTreeView x:Name="radTreeView" 
                                 IsOptionElementsEnabled="True" 
                                 IsTriStateMode="True" 
                                 ItemsSource="{StaticResource DataSource}" 
                                 ItemTemplate="{StaticResource ItemTemplate}" 
                                 ItemPrepared="radTreeView_ItemPrepared"/> 
  

  Switch to the code-behind and in the event handler add a code, synchronizing the CheckState property of the RadTreeViewItem object with the CheckState property of the DataItem object.

      private void radTreeView_ItemPrepared( object sender, Telerik.Windows.Controls.RadTreeViewItemPreparedEventArgs e ) 
      { 
          e.PreparedItem.CheckState = ( e.PreparedItem.Item as DataItem ).CheckState; 
      } 
  

      Private Sub radTreeView_ItemPrepared(ByVal sender As Object, ByVal e As Telerik.Windows.Controls.RadTreeViewItemPreparedEventArgs) 
          e.PreparedItem.CheckState = TryCast(e.PreparedItem.Item, DataItem).CheckState 
      End Sub 
  

• The example so far is almost complete. However, there are some drawbacks. The RadTreeViewItem's CheckState property is synchronized just once. If the user checks\unchecks a specific treeview item, the source object will not be updated. In order to solve this problem you should attach to the RadTreeViewItem's Checked and Unchecked events.

      private void radTreeView_ItemPrepared( object sender, Telerik.Windows.Controls.RadTreeViewItemPreparedEventArgs e ) 
      { 
          e.PreparedItem.CheckState = ( e.PreparedItem.Item as DataItem ).CheckState; 
          e.PreparedItem.Checked += new EventHandler<Telerik.Windows.RadRoutedEventArgs>( PreparedItem_Checked ); 
          e.PreparedItem.Unchecked += new EventHandler<Telerik.Windows.RadRoutedEventArgs>( PreparedItem_Unchecked ); 
      } 
   
      void PreparedItem_Unchecked( object sender, Telerik.Windows.RadRoutedEventArgs e ) 
      { 
          RadTreeViewItem item = sender as RadTreeViewItem; 
          if ( item != null ) 
          { 
              ( item.Item as DataItem ).CheckState = System.Windows.Automation.ToggleState.Off; 
          } 
      } 
   
      void PreparedItem_Checked( object sender, Telerik.Windows.RadRoutedEventArgs e ) 
      { 
          RadTreeViewItem item = sender as RadTreeViewItem; 
          if ( item != null ) 
          { 
              ( item.Item as DataItem ).CheckState = System.Windows.Automation.ToggleState.On; 
          } 
      } 
  

      Private Sub radTreeView_ItemPrepared(ByVal sender As Object, ByVal e As Telerik.Windows.Controls.RadTreeViewItemPreparedEventArgs) 
          e.PreparedItem.CheckState = TryCast(e.PreparedItem.Item, DataItem).CheckState 
          AddHandler e.PreparedItem.Checked, AddressOf PreparedItem_Checked 
          AddHandler e.PreparedItem.Unchecked, AddressOf PreparedItem_Unchecked 
      End Sub 
   
      Private Sub PreparedItem_Unchecked(ByVal sender As Object, ByVal e As Telerik.Windows.RadRoutedEventArgs) 
          Dim item As RadTreeViewItem = TryCast(sender, RadTreeViewItem) 
          If item IsNot Nothing Then 
              TryCast(item.Item, DataItem).CheckState = System.Windows.Automation.ToggleState.Off 
          End If 
      End Sub 
   
      Private Sub PreparedItem_Checked(ByVal sender As Object, ByVal e As Telerik.Windows.RadRoutedEventArgs) 
          Dim item As RadTreeViewItem = TryCast(sender, RadTreeViewItem) 
          If item IsNot Nothing Then 
              TryCast(item.Item, DataItem).CheckState = System.Windows.Automation.ToggleState.[On] 
          End If 
      End Sub 
  

See Also

• Events-Overview