LoadOnDemand in WPF TreeViewAdv (Classic)

19 Oct 20224 minutes to read

The LoadOnDemand feature enables users to load items dynamically when a particular TreeViewItem is expanded. Hence the items are loaded on demand and reduce the loading time.

1. To load items on demand:
   • LoadOnDemand event is used to load the sub-items when a particular item is expanded.
   • LoadingHeader is used to display the text while sub-items are being loaded.
   • IsLoadOnDemand value has to be set to true if the item is to be loaded on demand.
   XAML

   <syncfusion:TreeViewAdv x:Name="treeViewAdv" LoadOnDemand="treeViewAdv_LoadOnDemand">
   <syncfusion:TreeViewItemAdv Header="Root1" IsLoadOnDemand="True" LoadingHeader="Loading....." />
   <syncfusion:TreeViewItemAdv Header="Root2" IsLoadOnDemand="True" LoadingHeader="Loading....." />
   </syncfusion:TreeViewAdv>

   C#

   public partial class MainWindow : Window
   {
       public MainWindow()
       {
           InitializeComponent();
           timer = new DispatcherTimer();
           timer.Interval = new TimeSpan(0, 0, 0, 0, 800);
           timer.Tick += new EventHandler(timer_Tick);
       }
       private void timer_Tick(object sender, EventArgs e)
       {
           if(loadingitem!=null)
           {
               for (int i = 0; i <= 5; i++)
               {
                   loadingitem.Items.Add(new TreeViewItemAdv() { Header = "Node" + i });
               }
               loadingitem.IsLoadOnDemand = false;
               timer.Stop();
           }
       }
       private DispatcherTimer timer;
       private TreeViewItemAdv loadingitem;
       private void treeViewAdv_LoadOnDemand(object sender, LoadonDemandEventArgs args)
       {
           loadingitem = args.TreeViewItem as TreeViewItemAdv;
           timer.Start();
       }
   }

   VB.NET

   Partial Public Class MainWindow
   Inherits Window
   Public Sub New()
   InitializeComponent()
   timer = New DispatcherTimer()
   timer.Interval = New TimeSpan(0, 0, 0, 0, 800)
   AddHandler timer.Tick, AddressOf timer_Tick
   End Sub
   Private Sub timer_Tick(ByVal sender As Object, ByVal e As EventArgs)
   If loadingitem IsNot Nothing Then
   For i As Integer = 0 To 5
   loadingitem.Items.Add(New TreeViewItemAdv() With {.Header = "Node" & i})
   Next i
   loadingitem.IsLoadOnDemand = False
   timer.Stop()
   End If
   End Sub
   Private timer As DispatcherTimer
   Private loadingitem As TreeViewItemAdv
   Private Sub treeViewAdv_LoadOnDemand(ByVal sender As Object, ByVal args As LoadonDemandEventArgs)
   loadingitem = TryCast(args.TreeViewItem, TreeViewItemAdv)
   timer.Start()
   End Sub
   End Class