How to load data on demand using events in wpf treegrid

CS/App.xaml

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+<Application x:Class="OnDemandLoading.App"
+             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:syncfusion="http://schemas.syncfusion.com/wpf"
+             StartupUri="MainWindow.xaml">
+    <Application.Resources />
+</Application>

CS/App.xaml.cs

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+#region Copyright Syncfusion Inc. 2001 - 2015
+// Copyright Syncfusion Inc. 2001 - 2015. All rights reserved.
+// Use of this code is subject to the terms of our license.
+// A copy of the current license can be obtained at any time by e-mailing
+// licensing@syncfusion.com. Any infringement will be prosecuted under
+// applicable laws. 
+#endregion
+using System;
+using System.Collections.Generic;
+using System.Configuration;
+using System.Data;
+using System.Linq;
+using System.Windows;
+
+namespace OnDemandLoading
+{
+    /// <summary>
+    /// Interaction logic for App.xaml
+    /// </summary>
+    public partial class App : Application
+    {
+        public App()
+        {            
+        }
+    }
+}

CS/Behavior/RequestTreeItemsBehavior.cs

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+using Microsoft.Xaml.Behaviors;
+using Syncfusion.UI.Xaml.Grid;
+using Syncfusion.UI.Xaml.TreeGrid;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace OnDemandLoading
+{
+    class RequestTreeItemsBehavior : Behavior<SfTreeGrid>
+    {
+        ViewModel viewModel;
+        protected override void OnAttached()
+        {
+            base.OnAttached();
+            viewModel = this.AssociatedObject.DataContext as ViewModel;
+            this.AssociatedObject.RequestTreeItems += AssociatedObject_RequestTreeItems;
+
+        }
+
+        void AssociatedObject_RequestTreeItems(object sender, TreeGridRequestTreeItemsEventArgs args)
+        {
+            if (args.ParentItem == null)
+            {
+                //get the root list - get all employees who have no boss 
+                args.ChildItems = viewModel.EmployeeDetails.Where(x => x.ReportsTo == -1); //get all employees whose boss's id is -1 (no boss)
+            }
+            else //if ParentItem not null, then set args.ChildList to the child items for the given ParentItem.
+            {   //get the children of the parent object
+                EmployeeInfo emp = args.ParentItem as EmployeeInfo;
+                if (emp != null)
+                {
+                    //get all employees that report to the parent employee
+                    args.ChildItems = viewModel.GetReportees(emp.ID);
+                }
+            }
+        }       
+
+        protected override void OnDetaching()
+        {
+            base.OnDetaching();
+            this.AssociatedObject.RequestTreeItems -= AssociatedObject_RequestTreeItems;
+        }
+    }
+}

CS/MainWindow.xaml

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+<syncfusion:ChromelessWindow x:Class="OnDemandLoading.MainWindow"
+                             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+                             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"                             
+                             xmlns:local="clr-namespace:OnDemandLoading"
+                             xmlns:interactivity="http://schemas.microsoft.com/xaml/behaviors"
+                             xmlns:syncfusion="http://schemas.syncfusion.com/wpf"                             
+                             Icon="App.ico"
+                             WindowStartupLocation="CenterScreen">
+    <syncfusion:ChromelessWindow.DataContext>
+        <local:ViewModel />
+    </syncfusion:ChromelessWindow.DataContext>
+
+    <Grid>
+        <syncfusion:SfTreeGrid Name="treeGrid"
+                                       AutoGenerateColumns="False"                                       
+                                       ItemsSource="{Binding EmployeeDetails}">
+            <interactivity:Interaction.Behaviors>
+                <local:RequestTreeItemsBehavior />
+            </interactivity:Interaction.Behaviors>
+
+            <syncfusion:SfTreeGrid.Columns>
+                <syncfusion:TreeGridTextColumn HeaderText="First Name" MappingName="FirstName" />
+                <syncfusion:TreeGridTextColumn HeaderText="Employee ID"
+                                                       MappingName="ID"
+                                                       TextAlignment="Left" />
+
+                <syncfusion:TreeGridTextColumn HeaderText="Last Name" MappingName="LastName" />
+                <syncfusion:TreeGridTextColumn MappingName="Title" />
+                <syncfusion:TreeGridCurrencyColumn MappingName="Salary" />
+                <syncfusion:TreeGridTextColumn HeaderText="Reports To" MappingName="ReportsTo" />
+            </syncfusion:SfTreeGrid.Columns>
+        </syncfusion:SfTreeGrid>
+    </Grid>
+</syncfusion:ChromelessWindow>

CS/MainWindow.xaml.cs

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+#region Copyright Syncfusion Inc. 2001 - 2016
+// Copyright Syncfusion Inc. 2001 - 2016. All rights reserved.
+// Use of this code is subject to the terms of our license.
+// A copy of the current license can be obtained at any time by e-mailing
+// licensing@syncfusion.com. Any infringement will be prosecuted under
+// applicable laws. 
+#endregion
+using Syncfusion.Windows.Shared;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Windows;
+using System.Windows.Controls;
+using System.Windows.Data;
+using System.Windows.Documents;
+using System.Windows.Input;
+using System.Windows.Media;
+using System.Windows.Media.Imaging;
+using System.Windows.Navigation;
+using System.Windows.Shapes;
+
+namespace OnDemandLoading
+{
+    /// <summary>
+    /// Interaction logic for MainWindow.xaml
+    /// </summary>
+    public partial class MainWindow : ChromelessWindow
+    {
+        public MainWindow()
+        {
+            InitializeComponent();            
+        }
+    }
+}

CS/Model/EmployeeInfo.cs

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+#region Copyright Syncfusion Inc. 2001 - 2016
+// Copyright Syncfusion Inc. 2001 - 2016. All rights reserved.
+// Use of this code is subject to the terms of our license.
+// A copy of the current license can be obtained at any time by e-mailing
+// licensing@syncfusion.com. Any infringement will be prosecuted under
+// applicable laws. 
+#endregion
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using Syncfusion.Windows.Shared;
+using System.ComponentModel;
+using System.ComponentModel.DataAnnotations;
+
+namespace OnDemandLoading
+{
+    public class EmployeeInfo : NotificationObject//, IComparable<EmployeeInfo>
+    {
+        int _id;
+        /// <summary>
+        /// Gets or sets the ID.
+        /// </summary>
+        /// <value>The ID.</value>
+        public int ID
+        {
+            get
+            {
+                return _id;
+            }
+            set
+            {
+                _id = value;
+                RaisePropertyChanged("ID");
+            }
+        }
+        string _firstName;
+
+        /// <summary>
+        /// Gets or sets the first name.
+        /// </summary>
+        /// <value>The first name.</value>
+        public string FirstName
+        {
+            get
+            {
+                return _firstName;
+            }
+            set
+            {
+                _firstName = value;
+                RaisePropertyChanged("FirstName");
+            }
+        }
+        string _lastName;
+
+        /// <summary>
+        /// Gets or sets the last name.
+        /// </summary>
+        /// <value>The last name.</value>
+        public string LastName
+        {
+            get
+            {
+                return _lastName;
+            }
+            set
+            {
+                _lastName = value;
+                RaisePropertyChanged("LastName");
+            }
+        }
+        string _department;
+
+        /// <summary>
+        /// Gets or sets the department.
+        /// </summary>
+        /// <value>The department.</value>
+        public string Department
+        {
+            get
+            {
+                return _department;
+            }
+            set
+            {
+                _department = value;
+                RaisePropertyChanged("Department");
+            }
+        }
+        private string _title;
+
+        /// <summary>
+        /// Gets or sets the title.
+        /// </summary>
+        /// <value>The title.</value>
+        public string Title
+        {
+            get
+            {
+                return _title;
+            }
+            set
+            {
+                _title = value;
+                RaisePropertyChanged("Title");
+            }
+        }
+
+        double? _salary;
+        /// <summary>
+        /// Gets or sets the salary.
+        /// </summary>
+        /// <value>The salary.</value>
+        public double? Salary
+        {
+            get
+            {
+                return _salary;
+            }
+            set
+            {
+                _salary = value;
+                RaisePropertyChanged("Salary");
+            }
+        }
+
+        int _reportsTo;
+        /// <summary>
+        /// Gets or sets the reports to.
+        /// </summary>
+        /// <value>The reports to.</value>
+        public int ReportsTo
+        {
+            get
+            {
+                return _reportsTo;
+            }
+            set
+            {
+                _reportsTo = value;
+                RaisePropertyChanged("ReportsTo");
+            }
+        }
+
+        #region IComparable<Employee> Members
+
+        //public int CompareTo(EmployeeInfo other)
+        //{
+        //    // return this.reportsTo - other.reportsTo;
+        //    if (other == null)
+        //        return -1;
+
+        //    return this.ReportsTo.CompareTo(other.ReportsTo);
+        //}
+
+        #endregion
+    }
+}