TreeList Events

This article explains the events available in the Telerik TreeList for Blazor. They are grouped logically.

• CUD Events - events related to Creating, Updating and Deleting items
• Other Events - other events the treelist provides

CUD Events

The OnAdd, OnCreate, OnUpdate and OnDelete events let you get the data item that the user changed so you can transfer the user action to the actual data source.

The OnEdit and OnCancel events let you respond to user actions - when they want to edit an item and when they want to cancel changes on an item they have been editing. You can use them to, for example, prevent editing of certain items based on some condition.

You can read more about the CUD events in the Editing Overview article.

Other Events

• OnExpand and OnCollapse
• Command Button Click
• SelectedItemsChanged
• OnModelInit
• OnRowClick
• OnRowDoubleClick
• OnRowContextMenu
• OnRowRender
• OnRowDrop
• PageChanged
• PageSizeChanged

OnExpand and OnCollapse

The OnExpand event fires when the user clicks the expand arrow on a row that has children but they are collapsed. It receives arguments of type TreeListExpandEventArgs<T> where T is the model you bind the treelist to, and the Item field in the event arguments is the current model.

You can use OnExpand to know the user action and/or to load data on demand.

The OnCollapse event fires when the user collapses an expanded row through the collapse arrow. It receives arguments of type TreeListCollapseEventArgs<T> where T is the model you bind the treelist to, and the Item field in the event arguments is the current model.

If you set the ShouldRender field of the event arguments to true, the component will re-render after the event (it will call StateHasChanged()). This can be useful if you need to change its parameters or state during the event execution and especially if you need to execute async logic in the event handler.

Handle OnExpand and OnCollapse

@lastAction

<TelerikTreeList Data="@Data"
                 ItemsField="@(nameof(Employee.DirectReports))"
                 OnExpand="@OnExpand"
                 OnCollapse="@OnCollapse"
                 Pageable="true" Width="850px">
    <TreeListColumns>
        <TreeListColumn Field="Name" Expandable="true" Width="320px" />
        <TreeListColumn Field="Id" Editable="false" Width="120px" />
        <TreeListColumn Field="EmailAddress" Width="220px" />
        <TreeListColumn Field="HireDate" Width="220px" />
    </TreeListColumns>
</TelerikTreeList>

@code {
    public List<Employee> Data { get; set; }

    string lastAction { get; set; }

    // get when the user expands an item
    void OnExpand(TreeListExpandEventArgs args)
    {
        Employee currRow = args.Item as Employee;
        lastAction = $"The user expanded {currRow.Name} with ID {currRow.Id}";
    }

    // get when the user collapses an item
    void OnCollapse(TreeListCollapseEventArgs args)
    {
        Employee currRow = args.Item as Employee;
        lastAction = $"The user collapsed {currRow.Name} with ID {currRow.Id}";
    }

    // sample model

    public class Employee
    {
        // hierarchical data collections
        public List<Employee> DirectReports { get; set; }

        // data fields for display
        public int Id { get; set; }
        public string Name { get; set; }
        public string EmailAddress { get; set; }
        public DateTime HireDate { get; set; }
    }

    // data generation

    // used in this example for data generation and retrieval for CUD operations on the current view-model data
    public int LastId { get; set; } = 1;

    protected override async Task OnInitializedAsync()
    {
        Data = await GetTreeListData();
    }

    async Task<List<Employee>> GetTreeListData()
    {
        List<Employee> data = new List<Employee>();

        for (int i = 1; i < 15; i++)
        {
            Employee root = new Employee
            {
                Id = LastId,
                Name = $"root: {i}",
                EmailAddress = $"{i}@example.com",
                HireDate = DateTime.Now.AddYears(-i),
                DirectReports = new List<Employee>(), // prepare a collection for the child items, will be populated later in the code
            };
            data.Add(root);
            LastId++;

            for (int j = 1; j < 4; j++)
            {
                int currId = LastId;
                Employee firstLevelChild = new Employee
                {
                    Id = currId,
                    Name = $"first level child {j} of {i}",
                    EmailAddress = $"{currId}@example.com",
                    HireDate = DateTime.Now.AddDays(-currId),
                    DirectReports = new List<Employee>(), // collection for child nodes
                };
                root.DirectReports.Add(firstLevelChild); // populate the parent's collection
                LastId++;

                for (int k = 1; k < 3; k++)
                {
                    int nestedId = LastId;
                    // populate the parent's collection
                    firstLevelChild.DirectReports.Add(new Employee
                    {
                        Id = LastId,
                        Name = $"second level child {k} of {j} and {i}",
                        EmailAddress = $"{nestedId}@example.com",
                        HireDate = DateTime.Now.AddMinutes(-nestedId)
                    }); ;
                    LastId++;
                }
            }
        }

        return await Task.FromResult(data);
    }
}

Command Button Click

The command buttons of a treelist provide an OnClick event before firing their built-in command (such as opening a row for editing, or adding a new row). You can do this to implement some additional logic and to also handle custom commands - both from a Command Column, and from a Toolbar Button.

SelectedItemsChanged

Fires when the item selection is enabled and the user changes the selected item or items.

OnModelInit

The OnModelInit event fires before editing and adding new item in the component. The event allows you to:

• bind the component to a class that has no parameterless constructor

• bind the component to an interface

• bind the component to an abstract class

To achieve the desired behavior you can provide an instance of the model that the component is bound to in the OnModelInit event handler.

The different use-cases of the OnModelInit event

@* Bind the TreeList to a class without a parameterless constructor *@

@using System.ComponentModel.DataAnnotations

<TelerikTreeList Data="@Data"
                 EditMode="@TreeListEditMode.Popup"
                 OnModelInit="@OnModelInitHandler"
                 OnUpdate="@UpdateItem"
                 OnDelete="@DeleteItem"
                 OnCreate="@CreateItem"
                 OnCancel="@OnCancelHandler"
                 Pageable="true" ItemsField="@(nameof(Employee.DirectReports))"
                 Width="850px">
    <TreeListToolBarTemplate>
        <TreeListCommandButton Command="Add" Icon="@FontIcon.Plus">Add</TreeListCommandButton>
    </TreeListToolBarTemplate>
    <TreeListColumns>
        <TreeListCommandColumn Width="280px">
            <TreeListCommandButton Command="Add" Icon="@FontIcon.Plus">Add Child</TreeListCommandButton>
            <TreeListCommandButton Command="Edit" Icon="@FontIcon.Pencil">Edit</TreeListCommandButton>
            <TreeListCommandButton Command="Delete" Icon="@FontIcon.Trash">Delete</TreeListCommandButton>
            <TreeListCommandButton Command="Save" Icon="@FontIcon.Save" ShowInEdit="true">Update</TreeListCommandButton>
            <TreeListCommandButton Command="Cancel" Icon="@FontIcon.Cancel" ShowInEdit="true">Cancel</TreeListCommandButton>
        </TreeListCommandColumn>

        <TreeListColumn Field="Name" Expandable="true" Width="320px" />
        <TreeListColumn Field="Id" Editable="false" Width="120px" />
        <TreeListColumn Field="EmailAddress" Width="220px" />
        <TreeListColumn Field="HireDate" Width="220px" />
    </TreeListColumns>
</TelerikTreeList>


@code {
    public List<Employee> Data { get; set; }

    private Employee OnModelInitHandler()
    {
        return new Employee(1, "Test", "[e-mail]", DateTime.Today, null, false);
    }

    // Sample CUD operations for the local data
    async Task UpdateItem(TreeListCommandEventArgs args)
    {
        var item = args.Item as Employee;

        // perform actual data source operations here through your service
        await MyService.Update(item);

        // update the local view-model data with the service data
        await GetTreeListData();
    }

    async Task CreateItem(TreeListCommandEventArgs args)
    {
        var item = args.Item as Employee;
        var parentItem = args.ParentItem as Employee;

        // perform actual data source operations here through your service
        await MyService.Create(item, parentItem);

        // update the local view-model data with the service data
        await GetTreeListData();
    }

    async Task DeleteItem(TreeListCommandEventArgs args)
    {
        var item = args.Item as Employee;

        // perform actual data source operations here through your service
        await MyService.Delete(item);

        // update the local view-model data with the service data
        await GetTreeListData();
    }

    // OnCancel handler

    async Task OnCancelHandler(TreeListCommandEventArgs args)
    {
        Employee empl = args.Item as Employee;
        // if necessary, perform actual data source operation here through your service
    }


    // sample model

    public class Employee
    {
        public int Id { get; set; }

        [Required(ErrorMessage = "The employee must have a name")]
        public string Name { get; set; }
        [EmailAddress]
        public string EmailAddress { get; set; }
        public DateTime HireDate { get; set; }

        public List<Employee> DirectReports { get; set; }
        public bool HasChildren { get; set; }

        public Employee(int id, string name, string email, DateTime date, List<Employee> reports, bool hasChildren)
        {
            Id = id;
            Name = name;
            EmailAddress = email;
            HireDate = date;
            DirectReports = reports;
            HasChildren = hasChildren;
        }

        // Used for the editing so replacing the object in the view-model data
        // will treat it as the same object and keep its state - otherwise it will
        // collapse after editing is done, which is not what the user would expect
        public override bool Equals(object obj)
        {
            if (obj is Employee)
            {
                return this.Id == (obj as Employee).Id;
            }
            return false;
        }
    }

    // data generation

    async Task GetTreeListData()
    {
        Data = await MyService.Read();
    }

    protected override async Task OnInitializedAsync()
    {
        await GetTreeListData();
    }

    // the following static class mimics an actual data service that handles the actual data source
    // replace it with your actual service through the DI, this only mimics how the API can look like and works for this standalone page
    public static class MyService
    {
        private static List<Employee> _data { get; set; } = new List<Employee>();
        // used in this example for data generation and retrieval for CUD operations on the current view-model data
        private static int LastId { get; set; } = 1;

        public static async Task Create(Employee itemToInsert, Employee parentItem)
        {
            InsertItemRecursive(_data, itemToInsert, parentItem);
        }

        public static async Task<List<Employee>> Read()
        {
            if (_data.Count < 1)
            {
                for (int i = 1; i < 15; i++)
                {
                    Employee root = new Employee(LastId, $"root: {i}", $"{i}@example.com", DateTime.Now.AddYears(-i), new List<Employee>(), true);

                    _data.Add(root);

                    LastId++;

                    for (int j = 1; j < 4; j++)
                    {
                        int currId = LastId;

                        Employee firstLevelChild = new Employee(currId, $"first level child {j} of {i}", $"{currId}@example.com", DateTime.Now.AddDays(-currId), new List<Employee>(), true);

                        root.DirectReports.Add(firstLevelChild);
                        LastId++;

                        for (int k = 1; k < 3; k++)
                        {
                            int nestedId = LastId;

                            firstLevelChild.DirectReports.Add(new Employee(LastId, $"second level child {k} of {j} and {i}", $"{nestedId}@example.com", DateTime.Now.AddMinutes(-nestedId), null, false));
                        }
                    }
                }
            }

            return await Task.FromResult(_data);
        }

        public static async Task Update(Employee itemToUpdate)
        {
            UpdateItemRecursive(_data, itemToUpdate);
        }

        public static async Task Delete(Employee itemToDelete)
        {
            RemoveChildRecursive(_data, itemToDelete);
        }

        // sample helper methods for handling the view-model data hierarchy
        static void UpdateItemRecursive(List<Employee> items, Employee itemToUpdate)
        {
            for (int i = 0; i < items.Count; i++)
            {
                if (items[i].Id.Equals(itemToUpdate.Id))
                {
                    items[i] = itemToUpdate;
                    return;
                }

                if (items[i].DirectReports?.Count > 0)
                {
                    UpdateItemRecursive(items[i].DirectReports, itemToUpdate);
                }
            }
        }

        static void RemoveChildRecursive(List<Employee> items, Employee item)
        {
            for (int i = 0; i < items.Count(); i++)
            {
                if (item.Equals(items[i]))
                {
                    items.Remove(item);

                    return;
                }
                else if (items[i].DirectReports?.Count > 0)
                {
                    RemoveChildRecursive(items[i].DirectReports, item);

                    if (items[i].DirectReports.Count == 0)
                    {
                        items[i].HasChildren = false;
                    }
                }
            }
        }

        static void InsertItemRecursive(List<Employee> Data, Employee insertedItem, Employee parentItem)
        {
            insertedItem.Id = LastId++;
            if (parentItem != null)
            {
                parentItem.HasChildren = true;
                if (parentItem.DirectReports == null)
                {
                    parentItem.DirectReports = new List<Employee>();
                }

                parentItem.DirectReports.Insert(0, insertedItem);
            }
            else
            {
                Data.Insert(0, insertedItem);
            }
        }
    }
}

@* Bind the TreeList to an interface *@

@using System.ComponentModel.DataAnnotations

<TelerikTreeList Data="@Data"
                 EditMode="@TreeListEditMode.Popup"
                 OnModelInit="@OnModelInitHandler"
                 OnUpdate="@UpdateItem"
                 OnDelete="@DeleteItem"
                 OnCreate="@CreateItem"
                 OnCancel="@OnCancelHandler"
                 Pageable="true" ItemsField="@(nameof(Employee.DirectReports))"
                 Width="850px">
    <TreeListToolBarTemplate>
        <TreeListCommandButton Command="Add" Icon="@FontIcon.Plus">Add</TreeListCommandButton>
    </TreeListToolBarTemplate>
    <TreeListColumns>
        <TreeListCommandColumn Width="280px">
            <TreeListCommandButton Command="Add" Icon="@FontIcon.Plus">Add Child</TreeListCommandButton>
            <TreeListCommandButton Command="Edit" Icon="@FontIcon.Pencil">Edit</TreeListCommandButton>
            <TreeListCommandButton Command="Delete" Icon="@FontIcon.Trash">Delete</TreeListCommandButton>
            <TreeListCommandButton Command="Save" Icon="@FontIcon.Save" ShowInEdit="true">Update</TreeListCommandButton>
            <TreeListCommandButton Command="Cancel" Icon="@FontIcon.Cancel" ShowInEdit="true">Cancel</TreeListCommandButton>
        </TreeListCommandColumn>

        <TreeListColumn Field="Name" Expandable="true" Width="320px" />
        <TreeListColumn Field="Id" Editable="false" Width="120px" />
        <TreeListColumn Field="EmailAddress" Width="220px" />
        <TreeListColumn Field="HireDate" Width="220px" />
    </TreeListColumns>
</TelerikTreeList>


@code {
    public List<IEmployee> Data { get; set; }

    private Employee OnModelInitHandler()
    {
        return new Employee(1, "Test", "[e-mail]", DateTime.Today, null, false);
    }

    // Sample CUD operations for the local data
    async Task UpdateItem(TreeListCommandEventArgs args)
    {
        var item = args.Item as Employee;

        // perform actual data source operations here through your service
        await MyService.Update(item);

        // update the local view-model data with the service data
        await GetTreeListData();
    }

    async Task CreateItem(TreeListCommandEventArgs args)
    {
        var item = args.Item as Employee;
        var parentItem = args.ParentItem as Employee;

        // perform actual data source operations here through your service
        await MyService.Create(item, parentItem);

        // update the local view-model data with the service data
        await GetTreeListData();
    }

    async Task DeleteItem(TreeListCommandEventArgs args)
    {
        var item = args.Item as Employee;

        // perform actual data source operations here through your service
        await MyService.Delete(item);

        // update the local view-model data with the service data
        await GetTreeListData();
    }

    // OnCancel handler

    async Task OnCancelHandler(TreeListCommandEventArgs args)
    {
        Employee empl = args.Item as Employee;
        // if necessary, perform actual data source operation here through your service
    }


    // sample model
    public interface IEmployee
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public string EmailAddress { get; set; }
        public DateTime HireDate { get; set; }

        public List<IEmployee> DirectReports { get; set; }
        public bool HasChildren { get; set; }
    }

    public class Employee : IEmployee
    {
        public int Id { get; set; }

        [Required(ErrorMessage = "The employee must have a name")]
        public string Name { get; set; }
        [EmailAddress]
        public string EmailAddress { get; set; }
        public DateTime HireDate { get; set; }

        public List<IEmployee> DirectReports { get; set; }
        public bool HasChildren { get; set; }

        public Employee(int id, string name, string email, DateTime date, List<IEmployee> reports, bool hasChildren)
        {
            Id = id;
            Name = name;
            EmailAddress = email;
            HireDate = date;
            DirectReports = reports;
            HasChildren = hasChildren;
        }

        // Used for the editing so replacing the object in the view-model data
        // will treat it as the same object and keep its state - otherwise it will
        // collapse after editing is done, which is not what the user would expect
        public override bool Equals(object obj)
        {
            if (obj is Employee)
            {
                return this.Id == (obj as Employee).Id;
            }
            return false;
        }
    }

    // data generation

    async Task GetTreeListData()
    {
        Data = await MyService.Read();
    }

    protected override async Task OnInitializedAsync()
    {
        await GetTreeListData();
    }

    // the following static class mimics an actual data service that handles the actual data source
    // replace it with your actual service through the DI, this only mimics how the API can look like and works for this standalone page
    public static class MyService
    {
        private static List<IEmployee> _data { get; set; } = new List<IEmployee>();
        // used in this example for data generation and retrieval for CUD operations on the current view-model data
        private static int LastId { get; set; } = 1;

        public static async Task Create(Employee itemToInsert, Employee parentItem)
        {
            InsertItemRecursive(_data, itemToInsert, parentItem);
        }

        public static async Task<List<IEmployee>> Read()
        {
            if (_data.Count < 1)
            {
                for (int i = 1; i < 15; i++)
                {
                    Employee root = new Employee(LastId, $"root: {i}", $"{i}@example.com", DateTime.Now.AddYears(-i), new List<IEmployee>(), true);

                    _data.Add(root);

                    LastId++;

                    for (int j = 1; j < 4; j++)
                    {
                        int currId = LastId;

                        Employee firstLevelChild = new Employee(currId, $"first level child {j} of {i}", $"{currId}@example.com", DateTime.Now.AddDays(-currId), new List<IEmployee>(), true);

                        root.DirectReports.Add(firstLevelChild);
                        LastId++;

                        for (int k = 1; k < 3; k++)
                        {
                            int nestedId = LastId;

                            firstLevelChild.DirectReports.Add(new Employee(LastId, $"second level child {k} of {j} and {i}", $"{nestedId}@example.com", DateTime.Now.AddMinutes(-nestedId), null, false));
                        }
                    }
                }
            }

            return await Task.FromResult(_data);
        }

        public static async Task Update(Employee itemToUpdate)
        {
            UpdateItemRecursive(_data, itemToUpdate);
        }

        public static async Task Delete(Employee itemToDelete)
        {
            RemoveChildRecursive(_data, itemToDelete);
        }

        // sample helper methods for handling the view-model data hierarchy
        static void UpdateItemRecursive(List<IEmployee> items, Employee itemToUpdate)
        {
            for (int i = 0; i < items.Count; i++)
            {
                if (items[i].Id.Equals(itemToUpdate.Id))
                {
                    items[i] = itemToUpdate;
                    return;
                }

                if (items[i].DirectReports?.Count > 0)
                {
                    UpdateItemRecursive(items[i].DirectReports, itemToUpdate);
                }
            }
        }

        static void RemoveChildRecursive(List<IEmployee> items, Employee item)
        {
            for (int i = 0; i < items.Count(); i++)
            {
                if (item.Equals(items[i]))
                {
                    items.Remove(item);

                    return;
                }
                else if (items[i].DirectReports?.Count > 0)
                {
                    RemoveChildRecursive(items[i].DirectReports, item);

                    if (items[i].DirectReports.Count == 0)
                    {
                        items[i].HasChildren = false;
                    }
                }
            }
        }

        static void InsertItemRecursive(List<IEmployee> Data, Employee insertedItem, Employee parentItem)
        {
            insertedItem.Id = LastId++;
            if (parentItem != null)
            {
                parentItem.HasChildren = true;
                if (parentItem.DirectReports == null)
                {
                    parentItem.DirectReports = new List<IEmployee>();
                }

                parentItem.DirectReports.Insert(0, insertedItem);
            }
            else
            {
                Data.Insert(0, insertedItem);
            }
        }
    }
}

@* Bind the TreeList to an abstract class *@

@using System.ComponentModel.DataAnnotations

<TelerikTreeList Data="@Data"
                 EditMode="@TreeListEditMode.Popup"
                 OnModelInit="@OnModelInitHandler"
                 OnUpdate="@UpdateItem"
                 OnDelete="@DeleteItem"
                 OnCreate="@CreateItem"
                 OnCancel="@OnCancelHandler"
                 Pageable="true" ItemsField="@(nameof(Employee.DirectReports))"
                 Width="850px">
    <TreeListToolBarTemplate>
        <TreeListCommandButton Command="Add" Icon="@FontIcon.Plus">Add</TreeListCommandButton>
    </TreeListToolBarTemplate>
    <TreeListColumns>
        <TreeListCommandColumn Width="280px">
            <TreeListCommandButton Command="Add" Icon="@FontIcon.Plus">Add Child</TreeListCommandButton>
            <TreeListCommandButton Command="Edit" Icon="@FontIcon.Pencil">Edit</TreeListCommandButton>
            <TreeListCommandButton Command="Delete" Icon="@FontIcon.Trash">Delete</TreeListCommandButton>
            <TreeListCommandButton Command="Save" Icon="@FontIcon.Save" ShowInEdit="true">Update</TreeListCommandButton>
            <TreeListCommandButton Command="Cancel" Icon="@FontIcon.Cancel" ShowInEdit="true">Cancel</TreeListCommandButton>
        </TreeListCommandColumn>

        <TreeListColumn Field="Name" Expandable="true" Width="320px" />
        <TreeListColumn Field="Id" Editable="false" Width="120px" />
        <TreeListColumn Field="EmailAddress" Width="220px" />
        <TreeListColumn Field="HireDate" Width="220px" />
    </TreeListColumns>
</TelerikTreeList>


@code {
    public List<EmployeeBase> Data { get; set; }

    private Employee OnModelInitHandler()
    {
        return new Employee(1, "Test", "[e-mail]", DateTime.Today, null, false);
    }

    // Sample CUD operations for the local data
    async Task UpdateItem(TreeListCommandEventArgs args)
    {
        var item = args.Item as Employee;

        // perform actual data source operations here through your service
        await MyService.Update(item);

        // update the local view-model data with the service data
        await GetTreeListData();
    }

    async Task CreateItem(TreeListCommandEventArgs args)
    {
        var item = args.Item as Employee;
        var parentItem = args.ParentItem as Employee;

        // perform actual data source operations here through your service
        await MyService.Create(item, parentItem);

        // update the local view-model data with the service data
        await GetTreeListData();
    }

    async Task DeleteItem(TreeListCommandEventArgs args)
    {
        var item = args.Item as Employee;

        // perform actual data source operations here through your service
        await MyService.Delete(item);

        // update the local view-model data with the service data
        await GetTreeListData();
    }

    // OnCancel handler

    async Task OnCancelHandler(TreeListCommandEventArgs args)
    {
        Employee empl = args.Item as Employee;
        // if necessary, perform actual data source operation here through your service
    }


    // sample model
    public abstract class EmployeeBase
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public string EmailAddress { get; set; }
        public DateTime HireDate { get; set; }

        public List<EmployeeBase> DirectReports { get; set; }
        public bool HasChildren { get; set; }
    }

    public class Employee : EmployeeBase
    {
        public Employee(int id, string name, string email, DateTime date, List<EmployeeBase> reports, bool hasChildren)
        {
            Id = id;
            Name = name;
            EmailAddress = email;
            HireDate = date;
            DirectReports = reports;
            HasChildren = hasChildren;
        }

        // Used for the editing so replacing the object in the view-model data
        // will treat it as the same object and keep its state - otherwise it will
        // collapse after editing is done, which is not what the user would expect
        public override bool Equals(object obj)
        {
            if (obj is Employee)
            {
                return this.Id == (obj as Employee).Id;
            }
            return false;
        }
    }

    // data generation

    async Task GetTreeListData()
    {
        Data = await MyService.Read();
    }

    protected override async Task OnInitializedAsync()
    {
        await GetTreeListData();
    }

    // the following static class mimics an actual data service that handles the actual data source
    // replace it with your actual service through the DI, this only mimics how the API can look like and works for this standalone page
    public static class MyService
    {
        private static List<EmployeeBase> _data { get; set; } = new List<EmployeeBase>();
        // used in this example for data generation and retrieval for CUD operations on the current view-model data
        private static int LastId { get; set; } = 1;

        public static async Task Create(Employee itemToInsert, Employee parentItem)
        {
            InsertItemRecursive(_data, itemToInsert, parentItem);
        }

        public static async Task<List<EmployeeBase>> Read()
        {
            if (_data.Count < 1)
            {
                for (int i = 1; i < 15; i++)
                {
                    Employee root = new Employee(LastId, $"root: {i}", $"{i}@example.com", DateTime.Now.AddYears(-i), new List<EmployeeBase>(), true);

                    _data.Add(root);

                    LastId++;

                    for (int j = 1; j < 4; j++)
                    {
                        int currId = LastId;

                        Employee firstLevelChild = new Employee(currId, $"first level child {j} of {i}", $"{currId}@example.com", DateTime.Now.AddDays(-currId), new List<EmployeeBase>(), true);

                        root.DirectReports.Add(firstLevelChild);
                        LastId++;

                        for (int k = 1; k < 3; k++)
                        {
                            int nestedId = LastId;

                            firstLevelChild.DirectReports.Add(new Employee(LastId, $"second level child {k} of {j} and {i}", $"{nestedId}@example.com", DateTime.Now.AddMinutes(-nestedId), null, false));
                        }
                    }
                }
            }

            return await Task.FromResult(_data);
        }

        public static async Task Update(Employee itemToUpdate)
        {
            UpdateItemRecursive(_data, itemToUpdate);
        }

        public static async Task Delete(Employee itemToDelete)
        {
            RemoveChildRecursive(_data, itemToDelete);
        }

        // sample helper methods for handling the view-model data hierarchy
        static void UpdateItemRecursive(List<EmployeeBase> items, Employee itemToUpdate)
        {
            for (int i = 0; i < items.Count; i++)
            {
                if (items[i].Id.Equals(itemToUpdate.Id))
                {
                    items[i] = itemToUpdate;
                    return;
                }

                if (items[i].DirectReports?.Count > 0)
                {
                    UpdateItemRecursive(items[i].DirectReports, itemToUpdate);
                }
            }
        }

        static void RemoveChildRecursive(List<EmployeeBase> items, Employee item)
        {
            for (int i = 0; i < items.Count(); i++)
            {
                if (item.Equals(items[i]))
                {
                    items.Remove(item);

                    return;
                }
                else if (items[i].DirectReports?.Count > 0)
                {
                    RemoveChildRecursive(items[i].DirectReports, item);

                    if (items[i].DirectReports.Count == 0)
                    {
                        items[i].HasChildren = false;
                    }
                }
            }
        }

        static void InsertItemRecursive(List<EmployeeBase> Data, Employee insertedItem, Employee parentItem)
        {
            insertedItem.Id = LastId++;
            if (parentItem != null)
            {
                parentItem.HasChildren = true;
                if (parentItem.DirectReports == null)
                {
                    parentItem.DirectReports = new List<EmployeeBase>();
                }

                parentItem.DirectReports.Insert(0, insertedItem);
            }
            else
            {
                Data.Insert(0, insertedItem);
            }
        }
    }
}

OnRowClick

The OnRowClick event fires when the user:

• Clicks or taps on a data row.
• Hits Enter while the row has focus. This scenario requires enabled keyboard navigation (Navigable="true").

The event does not fire when the user:

• Clicks or taps on a command button;
• Selects a row via the built-in checkbox column;
• Expands or collapses the hierarchy;
• When the clicked row is in edit mode.

OnRowClick event fires before selection.

The OnRowClick event handler receives a TreeListRowClickEventArgs argument, which has the following properties.

Property	Type	Description
EventArgs	EventArgs	This object maps to MouseEventArgs or KeyboardEventArgs depending on the user action.
Item	object	The data item. Cast the object to your model type to access its members.
ShouldRender	bool	Sets if the component will re-render after the event via StateHasChanged() call. This can be useful if you need to change the component parameters or state during the event execution, and especially if you need to execute async logic in the event handler.

Using the TreeList OnRowClick event

@* Use the OnRowClick event for the TreeList *@

<TelerikTreeList Data="@Data"
                 IdField="Id" ParentIdField="ParentId"
                 Pageable="true" Width="850px" Height="400px" 
                 OnRowClick="@OnRowClickHander">
    <TreeListColumns>
        <TreeListColumn Field="Name" Expandable="true" Width="320px" />
        <TreeListColumn Field="Id" Width="120px" />
        <TreeListColumn Field="ParentId" Width="120px" />
        <TreeListColumn Field="EmailAddress" Width="120px" />
        <TreeListColumn Field="HireDate" Width="220px" />
    </TreeListColumns>
</TelerikTreeList>

@code {
    private void OnRowClickHander(TreeListRowClickEventArgs args)
    {
        var clickedRow = args.Item as Employee;
    }

    public List<Employee> Data { get; set; }

    protected override async Task OnInitializedAsync()
    {
        Data = await GetTreeListData();
    }

    // sample model

    public class Employee
    {
        // denote the parent-child relationship between items
        public int Id { get; set; }
        public int? ParentId { get; set; }

        // custom data fields for display
        public string Name { get; set; }
        public string EmailAddress { get; set; }
        public DateTime HireDate { get; set; }
    }

    // data generation

    async Task<List<Employee>> GetTreeListData()
    {
        List<Employee> data = new List<Employee>();

        for (int i = 1; i < 15; i++)
        {
            data.Add(new Employee
            {
                Id = i,
                ParentId = null, // indicates a root-level item
                Name = $"root: {i}",
                EmailAddress = $"{i}@example.com",
                HireDate = DateTime.Now.AddYears(-i)
            }); ;

            for (int j = 1; j < 4; j++)
            {
                int currId = i * 100 + j;
                data.Add(new Employee
                {
                    Id = currId,
                    ParentId = i,
                    Name = $"first level child {j} of {i}",
                    EmailAddress = $"{currId}@example.com",
                    HireDate = DateTime.Now.AddDays(-currId)
                });

                for (int k = 1; k < 3; k++)
                {
                    int nestedId = currId * 1000 + k;
                    data.Add(new Employee
                    {
                        Id = nestedId,
                        ParentId = currId,
                        Name = $"second level child {k} of {i} and {currId}",
                        EmailAddress = $"{nestedId}@example.com",
                        HireDate = DateTime.Now.AddMinutes(-nestedId)
                    }); ;
                }
            }
        }

        return await Task.FromResult(data);
    }
}

OnRowDoubleClick

The OnRowDoubleClick event fires when the user double-clicks or double-taps on a data row.

The event does not fire when the user:

• Clicks or taps on a command button;
• Selects a row via the built-in checkbox column;
• Expands or collapses the hierarchy;
• When the clicked row is in edit mode.

OnRowDoubleClick event fires before selection.

The OnRowDoubleClick event handler receives a TreeListRowClickEventArgs argument, which has the following properties.

Property	Type	Description
EventArgs	EventArgs	This object maps to MouseEventArgs or KeyboardEventArgs depending on the user action.
Item	object	The data item. Cast the object to your model type to access its members.
ShouldRender	bool	Sets if the component will re-render after the event via StateHasChanged() call. This can be useful if you need to change the component parameters or state during the event execution, and especially if you need to execute async logic in the event handler.

Using the TreeList OnRowDoubleClick event

@* Use the OnRowDoubleClick event for the TreeList. *@ 

<TelerikTreeList Data="@Data"
                 IdField="Id" ParentIdField="ParentId"
                 Pageable="true" Width="850px" Height="400px" 
                 OnRowDoubleClick="@OnRowDoubleClickHander">
    <TreeListColumns>
        <TreeListColumn Field="Name" Expandable="true" Width="320px" />
        <TreeListColumn Field="Id" Width="120px" />
        <TreeListColumn Field="ParentId" Width="120px" />
        <TreeListColumn Field="EmailAddress" Width="120px" />
        <TreeListColumn Field="HireDate" Width="220px" />
    </TreeListColumns>
</TelerikTreeList>

@code {
    private void OnRowDoubleClickHander(TreeListRowClickEventArgs args)
    {
        var clickedRow = args.Item as Employee;
    }

    public List<Employee> Data { get; set; }

    protected override async Task OnInitializedAsync()
    {
        Data = await GetTreeListData();
    }

    // sample model

    public class Employee
    {
        // denote the parent-child relationship between items
        public int Id { get; set; }
        public int? ParentId { get; set; }

        // custom data fields for display
        public string Name { get; set; }
        public string EmailAddress { get; set; }
        public DateTime HireDate { get; set; }
    }

    // data generation

    async Task<List<Employee>> GetTreeListData()
    {
        List<Employee> data = new List<Employee>();

        for (int i = 1; i < 15; i++)
        {
            data.Add(new Employee
            {
                Id = i,
                ParentId = null, // indicates a root-level item
                Name = $"root: {i}",
                EmailAddress = $"{i}@example.com",
                HireDate = DateTime.Now.AddYears(-i)
            }); ;

            for (int j = 1; j < 4; j++)
            {
                int currId = i * 100 + j;
                data.Add(new Employee
                {
                    Id = currId,
                    ParentId = i,
                    Name = $"first level child {j} of {i}",
                    EmailAddress = $"{currId}@example.com",
                    HireDate = DateTime.Now.AddDays(-currId)
                });

                for (int k = 1; k < 3; k++)
                {
                    int nestedId = currId * 1000 + k;
                    data.Add(new Employee
                    {
                        Id = nestedId,
                        ParentId = currId,
                        Name = $"second level child {k} of {i} and {currId}",
                        EmailAddress = $"{nestedId}@example.com",
                        HireDate = DateTime.Now.AddMinutes(-nestedId)
                    }); ;
                }
            }
        }

        return await Task.FromResult(data);
    }
}

OnRowContextMenu

The OnRowContextMenu event fires when the user:

• Right-clicks or taps-and-holds a data row;
• Hits the context menu keyboard button while the row has focus. This scenario requires enabled keyboard navigation (Navigable="true").

Use OnRowContextMenu to integrate the Context menu with the table rows.

The OnRowContextMenu event handler receives a TreeListRowClickEventArgs argument, which has the following properties.

Property	Type	Description
EventArgs	EventArgs	This object maps to MouseEventArgs or KeyboardEventArgs depending on the user action.
Item	object	The data item. Cast the object to your model type to access its members.
ShouldRender	bool	Sets if the component will re-render after the event via StateHasChanged() call. This can be useful if you need to change the component parameters or state during the event execution, and especially if you need to execute async logic in the event handler.

Using the TreeList OnRowContextMenu event

@* Get the row model from a context menu action (right click/long tap) *@

<TelerikTreeList Data="@Data"
                 IdField="Id" 
                 ParentIdField="ParentId"
                 Pageable="true"
                 Width="850px"
                 Height="400px" 
                 OnRowContextMenu="@OnRowContextMenuHandler">
    <TreeListColumns>
        <TreeListColumn Field="Name" Expandable="true" Width="320px" />
        <TreeListColumn Field="Id" Width="120px" />
        <TreeListColumn Field="ParentId" Width="120px" />
        <TreeListColumn Field="EmailAddress" Width="120px" />
        <TreeListColumn Field="HireDate" Width="220px" />
    </TreeListColumns>
</TelerikTreeList>

<br />

@logger

@code {
    public string logger { get; set; } = String.Empty;

    private void OnRowContextMenuHandler(TreeListRowClickEventArgs args)
    {
        var clickedRow = args.Item as Employee;

        logger = $"OnRowContextMenu event fired from right clicking on {clickedRow.Name}";


        if (args.EventArgs is KeyboardEventArgs keyboardEventArgs)
        {
            Console.WriteLine($"The user pressed {keyboardEventArgs.Key} on row {model.Name}");
        }
        else if (args.EventArgs is MouseEventArgs mouseEventArgs)
        {
            Console.WriteLine($"The user clicked {mouseEventArgs.ClientX} {mouseEventArgs.ClientY} on row {model.Name}");
        }
    }

    public List<Employee> Data { get; set; }

    protected override async Task OnInitializedAsync()
    {
        Data = await GetTreeListData();
    }

    // sample model

    public class Employee
    {
        // denote the parent-child relationship between items
        public int Id { get; set; }
        public int? ParentId { get; set; }

        // custom data fields for display
        public string Name { get; set; }
        public string EmailAddress { get; set; }
        public DateTime HireDate { get; set; }
    }

    // data generation

    async Task<List<Employee>> GetTreeListData()
    {
        List<Employee> data = new List<Employee>();

        for (int i = 1; i < 15; i++)
        {
            data.Add(new Employee
            {
                Id = i,
                ParentId = null, // indicates a root-level item
                Name = $"root: {i}",
                EmailAddress = $"{i}@example.com",
                HireDate = DateTime.Now.AddYears(-i)
            }); ;

            for (int j = 1; j < 4; j++)
            {
                int currId = i * 100 + j;
                data.Add(new Employee
                {
                    Id = currId,
                    ParentId = i,
                    Name = $"first level child {j} of {i}",
                    EmailAddress = $"{currId}@example.com",
                    HireDate = DateTime.Now.AddDays(-currId)
                });

                for (int k = 1; k < 3; k++)
                {
                    int nestedId = currId * 1000 + k;
                    data.Add(new Employee
                    {
                        Id = nestedId,
                        ParentId = currId,
                        Name = $"second level child {k} of {i} and {currId}",
                        EmailAddress = $"{nestedId}@example.com",
                        HireDate = DateTime.Now.AddMinutes(-nestedId)
                    }); ;
                }
            }
        }

        return await Task.FromResult(data);
    }
}

OnRowRender

This event fires upon the rendering of the TreeList rows. It receives an argument of type TreeListRowRenderEventArgs which exposes the following fields:

• Item - an object you can cast to your model class to obtain the current data item.
• Class - the CSS class that will be applied to the rows of the TreeList. The CSS rules that are set for that class will be visibly rendered on the TreeList rows.

Use the OnRowRender event to apply custom format to TreeList rows based on certain condition

@* Conditional styling/formatting for a row *@

<style>
    .k-treelist tr.myCustomTreeListRowFormatting,
    .k-treelist tr.myCustomTreeListRowFormatting:hover {
        background-color: blue;
        color: white;
        font-size: 10px;
        font-weight: bolder;
    }
</style>

<TelerikTreeList Data="@Data"
                 ItemsField="@(nameof(Employee.DirectReports))"
                 Pageable="true" Width="850px" OnRowRender="@OnRowRenderHandler">
    <TreeListColumns>
        <TreeListColumn Field="Name" Expandable="true" Width="320px" />
        <TreeListColumn Field="Id" Width="120px" Visible="false" />
        <TreeListColumn Field="EmailAddress" Width="220px" />
        <TreeListColumn Field="HireDate" Width="220px" />
    </TreeListColumns>
</TelerikTreeList>

@code {
    void OnRowRenderHandler(TreeListRowRenderEventArgs args)
    {
        var item = args.Item as Employee;

        if (item.Id.Equals(3))
        {
            args.Class = "myCustomTreeListRowFormatting";
        }
    }

    public List<Employee> Data { get; set; }

    public class Employee
    {
        public List<Employee> DirectReports { get; set; }

        public int Id { get; set; }
        public string Name { get; set; }
        public string EmailAddress { get; set; }
        public DateTime HireDate { get; set; }
    }

    public int LastId { get; set; } = 1;

    protected override async Task OnInitializedAsync()
    {
        Data = await GetTreeListData();
    }

    async Task<List<Employee>> GetTreeListData()
    {
        List<Employee> data = new List<Employee>();

        for (int i = 1; i < 15; i++)
        {
            Employee root = new Employee
            {
                Id = LastId,
                Name = $"root: {i}",
                EmailAddress = $"{i}@example.com",
                HireDate = DateTime.Now.AddYears(-i),
                DirectReports = new List<Employee>()
            };
            data.Add(root);
            LastId++;

            for (int j = 1; j < 4; j++)
            {
                int currId = LastId;
                Employee firstLevelChild = new Employee
                {
                    Id = currId,
                    Name = $"first level child {j} of {i}",
                    EmailAddress = $"{currId}@example.com",
                    HireDate = DateTime.Now.AddDays(-currId),
                    DirectReports = new List<Employee>(),
                };
                root.DirectReports.Add(firstLevelChild);
                LastId++;

                for (int k = 1; k < 3; k++)
                {
                    int nestedId = LastId;
                    // populate the parent's collection
                    firstLevelChild.DirectReports.Add(new Employee
                    {
                        Id = LastId,
                        Name = $"second level child {k} of {j} and {i}",
                        EmailAddress = $"{nestedId}@example.com",
                        HireDate = DateTime.Now.AddMinutes(-nestedId)
                    }); ;
                    LastId++;
                }
            }
        }

        return await Task.FromResult(data);
    }
}

The result from the code snippet above

OnRowDrop

The OnRowDrop event fires when the user drags and drops rows in the TreeList or between TreeLists. You can read more on setting it up and using the TreeList row dragging feature in the Row Drag and Drop article.

PageChanged

The event fires when the user pages the treelist.

@result

<TelerikTreeList Data="@Data"
                 Pageable="true" PageChanged="@PageChangedHandler"
                 IdField="Id" ParentIdField="ParentId"
                 Width="650px">
    <TreeListColumns>
        <TreeListColumn Field="Name" Expandable="true" Width="300px"></TreeListColumn>
        <TreeListColumn Field="Id"></TreeListColumn>
    </TreeListColumns>
</TelerikTreeList>

@code {
    public List<Employee> Data { get; set; }

    string result { get; set; }
    async Task PageChangedHandler(int currPage)
    {
        result = $"the user is now on page {currPage}. Note - the indexes are 1-based, not 0-based";
    }

    protected override async Task OnInitializedAsync()
    {
        Data = await GetTreeListData();
    }

    // sample models and data generation

    public class Employee
    {
        public int Id { get; set; }
        public int? ParentId { get; set; }
        public string Name { get; set; }
    }

    async Task<List<Employee>> GetTreeListData()
    {
        List<Employee> data = new List<Employee>();

        for (int i = 1; i < 15; i++)
        {
            data.Add(new Employee
            {
                Id = i,
                ParentId = null,
                Name = $"root: {i}"
            });

            for (int j = 2; j < 5; j++)
            {
                int currId = i * 100 + j;
                data.Add(new Employee
                {
                    Id = currId,
                    ParentId = i,
                    Name = $"first level child of {i}"
                });

                for (int k = 3; k < 5; k++)
                {
                    data.Add(new Employee
                    {
                        Id = currId * 1000 + k,
                        ParentId = currId,
                        Name = $"second level child of {i} and {currId}"
                    }); ;
                }
            }
        }

        return await Task.FromResult(data);
    }
}

PageSizeChanged

The PageSizeChanged event fires when the user changes the page size via the pager DropDownList. The existence of this event also ensures that the TreeList PageSize attribute supports two-way binding.

If the user selects the "All" option from the page size DropDownList, the PageSizeChanged event will receive the total item count as an argument.

Make sure to update the current page size when using the event.

Handle PageSizeChanged

<TelerikTreeList Data="@Data"
                 Pageable="true"
                 @bind-Page="@CurrentPage"
                 PageSize="@PageSize"
                 PageSizeChanged="@PageSizeChangedHandler"
                 IdField="Id" ParentIdField="ParentId"
                 Width="650px">
    <TreeListSettings>
        <TreeListPagerSettings PageSizes="@PageSizes" />
    </TreeListSettings>
    <TreeListColumns>
        <TreeListColumn Field="Name" Expandable="true" Width="300px"></TreeListColumn>
        <TreeListColumn Field="Id"></TreeListColumn>
    </TreeListColumns>
</TelerikTreeList>

@code {
    int PageSize { get; set; } = 15;
    int CurrentPage { get; set; } = 3;

    protected List<int?> PageSizes { get; set; } = new List<int?> { 15, 30, null };

    void PageSizeChangedHandler(int newPageSize)
    {
        PageSize = newPageSize;
    }

    public List<Employee> Data { get; set; }

    protected override async Task OnInitializedAsync()
    {
        Data = await GetTreeListData();
    }

    // sample models and data generation

    public class Employee
    {
        public int Id { get; set; }
        public int? ParentId { get; set; }
        public string Name { get; set; }
    }

    async Task<List<Employee>> GetTreeListData()
    {
        List<Employee> data = new List<Employee>();

        for (int i = 1; i < 15; i++)
        {
            data.Add(new Employee
            {
                Id = i,
                ParentId = null,
                Name = $"root: {i}"
            });

            for (int j = 2; j < 5; j++)
            {
                int currId = i * 100 + j;
                data.Add(new Employee
                {
                    Id = currId,
                    ParentId = i,
                    Name = $"first level child of {i}"
                });

                for (int k = 3; k < 5; k++)
                {
                    data.Add(new Employee
                    {
                        Id = currId * 1000 + k,
                        ParentId = currId,
                        Name = $"second level child of {i} and {currId}"
                    }); ;
                }
            }
        }

        return await Task.FromResult(data);
    }
}

See Also

• TreeList Overview
• TreeList Column Events
• TreeList Editing Overview