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dimodi merged 1 commit into from
Jul 15, 2026
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Merge treelist-excel-3796 into production #3802

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348 changes: 348 additions & 0 deletions components/treelist/export/events.md
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---
title: Export Events
page_title: TreeList - Export Events
description: Learn about the Blazor TreeList events related to exporting the component data.
slug: treelist-export-events
tags: telerik,blazor,treelist,export,events
published: True
position: 15
components: ["treelist"]
---

# Export Events

You can customize the files exported to Excel by using the [OnBeforeExport](#onbeforeexport) and the [OnAfterExport](#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`&mdash;`List<TreeListExcelExportColumn>`&mdash;A collection of all exportable columns in the TreeList. These are all visible `TreeListColumn` instances. You can customize the following attributes of the TreeList column before exporting it into Excel:

* `Width`&mdash;Define the width of the column **in pixels**.
* `Title`&mdash;Define the column title to be shown in the Excel file header.
* `NumberFormat`&mdash;Provide an Excel-compatible number/date format
* `Field`&mdash;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`&mdash;`IEnumerable<object>`&mdash;Assign a custom collection of data to be exported to Excel.

* `IsCancelled`&mdash; `bool`&mdash;Cancel the `OnBeforeExcel` event by setting the `isCancelled` property to `true`.

>caption Using the TreeList OnBeforeExport with Excel export

````RAZOR
@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](#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`&mdash;`MemoryStream`&mdash;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 new `MemoryStream` instance. Then, use [Telerik Document Processing](slug:dpl-in-blazor) to make changes to the exported file, for example, [apply custom cell formatting with RadSpreadProcessing](slug:grid-kb-custom-cell-formatting-with-radspreadprocessing).

>caption Get the stream of the exported Excel file

````RAZOR Excel
<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
}
````

## See Also

* [TreeList Excel Export](slug:treelist-export-excel)
* [Custom cell formatting of the exported file with RadSpreadProcessing](slug:grid-kb-custom-cell-formatting-with-radspreadprocessing)
* [Custom cell formatting of the exported file with RadSpreadStreamProcessing](slug:grid-kb-custom-cell-formatting-with-radspreadstreamprocessing)
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