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Export Events
Updated on Jul 15, 2026
You can customize the files exported to Excel by using the OnBeforeExport and the OnAfterExport events exposed to the TreeListExcelExport tag.
OnBeforeExport
The OnBeforeExport event fires after the user clicks the ExcelExport command button and before the export process starts. You can use the event to configure the exported TreeList columns or change the exported data. The event handler receives a TreeListBeforeExcelExportEventArgs object, which provides the following properties:
-
Columns—List<TreeListExcelExportColumn>—A collection of all exportable columns in the TreeList. These are all visibleTreeListColumninstances. You can customize the following attributes of the TreeList column before exporting it into Excel:Width—Define the width of the column in pixels.Title—Define the column title to be shown in the Excel file header.NumberFormat—Provide an Excel-compatible number/date formatField—Set the data bound field of the column.
To export a hidden TreeList column that has its Visible parameter set to false, you can manually define an instance of the TreeListExcelExportColumn in the handler for the OnBeforeExport event and add that column to the args.Columns collection.
-
Data—IEnumerable<object>—Assign a custom collection of data to be exported to Excel. -
IsCancelled—bool—Cancel theOnBeforeExcelevent by setting theisCancelledproperty totrue.
Using the TreeList OnBeforeExport with Excel export
@using Telerik.Documents.SpreadsheetStreaming
<TelerikTreeList @ref="@TreeListRef"
Data="@TreeListData"
IdField="@nameof(Employee.Id)"
Height="400px"
Pageable="true">
<TreeListExport>
<TreeListExcelExport AllPages="true"
ExpandAll="true"
FileName="telerik-treelist-export"
OnBeforeExport="@OnTreeListBeforeExport" />
</TreeListExport>
<TreeListToolBarTemplate>
<TreeListCommandButton Command="ExcelExport" Icon="@SvgIcon.FileExcel">Export to Excel</TreeListCommandButton>
</TreeListToolBarTemplate>
<TreeListColumns>
<TreeListColumn Field="@nameof(Employee.Name)" Expandable="true" Width="300px" />
<TreeListColumn Field="@nameof(Employee.Salary)" DisplayFormat="{0:C2}" Width="120px" />
<TreeListColumn Field="@nameof(Employee.HireDate)" DisplayFormat="{0:d}" Width="180px" />
<TreeListColumn Field="@nameof(Employee.IsDriver)" Visible="false" />
</TreeListColumns>
</TelerikTreeList>
@code {
private TelerikTreeList<Employee>? TreeListRef;
private IEnumerable<Employee>? TreeListData { get; set; }
private EmployeeService TreeListEmployeeService { get; set; } = new();
private void OnTreeListBeforeExport(TreeListBeforeExcelExportEventArgs args)
{
// Export the hidden IsDriver column that has Visible="false"
var exportableHiddenColumn = new TreeListExcelExportColumn()
{
Title = "Is Driver",
Field = nameof(Employee.IsDriver)
};
args.Columns.Add(exportableHiddenColumn);
// Customize the Width of the first exported column
args.Columns[0].Width = "360px";
// Change the format of the Salary column
// BuiltInNumberFormats is part of the Telerik.Documents.SpreadsheetStreaming namespace
args.Columns[1].NumberFormat = BuiltInNumberFormats.GetCurrency2();
// Change the format and title of the HireDate column
args.Columns[2].NumberFormat = BuiltInNumberFormats.GetShortDate();
args.Columns[2].Title = "Hired On";
// Set IsCancelled to true if you want to prevent exporting
// args.IsCancelled = false;
}
protected override async Task OnInitializedAsync()
{
TreeListData = await TreeListEmployeeService.Read();
}
public class Employee
{
public int Id { get; set; }
public bool HasChildren { get; set; }
public List<Employee>? Items { get; set; }
public string Name { get; set; } = string.Empty;
public string Notes { get; set; } = string.Empty;
public decimal? Salary { get; set; }
public DateTime? HireDate { get; set; }
public bool IsDriver { get; set; }
public override bool Equals(object? obj)
{
return obj is Employee && ((Employee)obj).Id == Id;
}
public override int GetHashCode()
{
return base.GetHashCode();
}
}
#region Data Service
public class EmployeeService
{
private List<Employee> Items { get; set; } = new();
private readonly int TreeLevelCount;
private readonly int RootItemCount;
private readonly int ChildItemCount;
private int LastId { get; set; }
private readonly Random Rnd = Random.Shared;
public async Task<List<Employee>> Read()
{
await SimulateAsyncOperation();
return Items;
}
private async Task SimulateAsyncOperation()
{
await Task.Delay(100);
}
private void PopulateItems(List<Employee> items, int level)
{
for (int i = 1; i <= (level == 1 ? RootItemCount : ChildItemCount); i++)
{
var itemId = ++LastId;
Employee newItem = new Employee()
{
Id = itemId,
HasChildren = level < TreeLevelCount,
Name = $"Employee Name {itemId} ({level}-{i})",
Notes = $"Multi-line\nnotes {itemId}",
Salary = Rnd.Next(1_000, 10_000) * 1.23m,
HireDate = DateTime.Today.AddDays(-Rnd.Next(365, 3650)),
IsDriver = itemId % 2 == 0
};
items.Add(newItem);
}
if (level < TreeLevelCount)
{
PopulateChildren(items, level + 1);
}
}
private void PopulateChildren(List<Employee> items, int level)
{
foreach (var item in items)
{
item.Items = new List<Employee>();
PopulateItems(item.Items, level);
}
}
public EmployeeService(int treeLevelCount = 3, int rootItemCount = 5, int childItemCount = 3)
{
TreeLevelCount = treeLevelCount;
RootItemCount = rootItemCount;
ChildItemCount = childItemCount;
List<Employee> items = new();
PopulateItems(items, 1);
Items = items;
}
}
#endregion Data Service
}OnAfterExport
The OnAfterExport event fires after OnBeforeExport and before the generated file is provided to the user. You can use the event to make changes to the exported file. The event handler receives a TreeListAfterExcelExportEventArgs object, which provides the following properties:
Stream—MemoryStream—The output of the Excel export as a memory stream. The stream itself is finalized, so that the resource does not leak. To read and work with the stream, clone its available binary data to a newMemoryStreaminstance. Then, use Telerik Document Processing to make changes to the exported file, for example, apply custom cell formatting with RadSpreadProcessing.
Get the stream of the exported Excel file
<TelerikTreeList @ref="@TreeListRef"
Data="@TreeListData"
IdField="@nameof(Employee.Id)"
Height="400px"
Pageable="true">
<TreeListExport>
<TreeListExcelExport AllPages="true"
ExpandAll="true"
FileName="telerik-treelist-export"
OnAfterExport="@OnTreeListAfterExport" />
</TreeListExport>
<TreeListToolBarTemplate>
<TreeListCommandButton Command="ExcelExport" Icon="@SvgIcon.FileExcel">Export to Excel</TreeListCommandButton>
</TreeListToolBarTemplate>
<TreeListColumns>
<TreeListColumn Field="@nameof(Employee.Name)" Expandable="true" Width="300px" />
<TreeListColumn Field="@nameof(Employee.Salary)" DisplayFormat="{0:C2}" Width="120px" />
<TreeListColumn Field="@nameof(Employee.HireDate)" DisplayFormat="{0:d}" Width="180px" />
<TreeListColumn Field="@nameof(Employee.IsDriver)" Visible="false" />
</TreeListColumns>
</TelerikTreeList>
@code {
private TelerikTreeList<Employee>? TreeListRef;
private IEnumerable<Employee>? TreeListData { get; set; }
private EmployeeService TreeListEmployeeService { get; set; } = new();
private void OnTreeListAfterExport(TreeListAfterExcelExportEventArgs args)
{
byte[] streamBytes = args.Stream.ToArray();
MemoryStream excelStream = new MemoryStream(streamBytes);
}
protected override async Task OnInitializedAsync()
{
TreeListData = await TreeListEmployeeService.Read();
}
public class Employee
{
public int Id { get; set; }
public bool HasChildren { get; set; }
public List<Employee>? Items { get; set; }
public string Name { get; set; } = string.Empty;
public string Notes { get; set; } = string.Empty;
public decimal? Salary { get; set; }
public DateTime? HireDate { get; set; }
public bool IsDriver { get; set; }
public override bool Equals(object? obj)
{
return obj is Employee && ((Employee)obj).Id == Id;
}
public override int GetHashCode()
{
return base.GetHashCode();
}
}
#region Data Service
public class EmployeeService
{
private List<Employee> Items { get; set; } = new();
private readonly int TreeLevelCount;
private readonly int RootItemCount;
private readonly int ChildItemCount;
private int LastId { get; set; }
private readonly Random Rnd = Random.Shared;
public async Task<List<Employee>> Read()
{
await SimulateAsyncOperation();
return Items;
}
private async Task SimulateAsyncOperation()
{
await Task.Delay(100);
}
private void PopulateItems(List<Employee> items, int level)
{
for (int i = 1; i <= (level == 1 ? RootItemCount : ChildItemCount); i++)
{
var itemId = ++LastId;
Employee newItem = new Employee()
{
Id = itemId,
HasChildren = level < TreeLevelCount,
Name = $"Employee Name {itemId} ({level}-{i})",
Notes = $"Multi-line\nnotes {itemId}",
Salary = Rnd.Next(1_000, 10_000) * 1.23m,
HireDate = DateTime.Today.AddDays(-Rnd.Next(365, 3650)),
IsDriver = itemId % 2 == 0
};
items.Add(newItem);
}
if (level < TreeLevelCount)
{
PopulateChildren(items, level + 1);
}
}
private void PopulateChildren(List<Employee> items, int level)
{
foreach (var item in items)
{
item.Items = new List<Employee>();
PopulateItems(item.Items, level);
}
}
public EmployeeService(int treeLevelCount = 3, int rootItemCount = 5, int childItemCount = 3)
{
TreeLevelCount = treeLevelCount;
RootItemCount = rootItemCount;
ChildItemCount = childItemCount;
List<Employee> items = new();
PopulateItems(items, 1);
Items = items;
}
}
#endregion Data Service
}