If the ComboBox Value is set during initialization and the ValueMapper executes too fast and before the component has rendered, its Value doesn't show.

The problem also occurs in the MultiColumnComboBox.

Possible workarounds:

• Set the component Value a bit later.
• Delay the ValueMapper execution until OnAfterRenderAsync fires.
• Rebind() the ComboBox in OnAfterRenderAsync. This will fire OnRead again.
• Render the ComboBox conditionally in the first OnAfterRenderAsync call.

To reproduce:

@using Telerik.DataSource
@using Telerik.DataSource.Extensions

<p>ComboBox Value: @ComboBoxValue</p>

<TelerikComboBox ItemHeight="30"
                 OnRead="@OnComboBoxRead"
                 PageSize="20"
                 ScrollMode="@DropDownScrollMode.Virtual"
                 TItem="@ListItem"
                 TValue="@(int?)"
                 @bind-Value="@ComboBoxValue"
                 ValueMapper="@ComboBoxValueMapper"
                 Width="240px" />

@code {
    private List<ListItem>? ComboBoxData { get; set; }

    private int? ComboBoxValue { get; set; } = 3;

    private async Task OnComboBoxRead(ReadEventArgs args)
    {
        DataSourceResult result = await ComboBoxData.ToDataSourceResultAsync(args.Request);

        args.Data = result.Data;
        args.Total = result.Total;
    }

    private async Task<ListItem?> ComboBoxValueMapper(int? selectValue)
    {
        // Triggers the bug
        await Task.Yield();

        ListItem? result = ComboBoxData?.FirstOrDefault(x => selectValue == x.Value);

        return result;
    }

    protected override void OnInitialized()
    {
        ComboBoxData = Enumerable
            .Range(1, 1234)
            .Select(x => new ListItem()
                {
                    Value = x,
                    Text = $"Item {x}"
                })
            .ToList();
    }

    public class ListItem
    {
        public int Value { get; set; }
        public string Text { get; set; } = string.Empty;
    }
}

The DropDownButton and SplitButton exhibit the following accessibility issues:

• The screen reader cannot read the items in the DropDownButton and SplitButton popup.
• When the DropDownButton is opened with Enter, the user cannot navigate the dropdown items with the arrow keys (tested in NVDA).

I am resetting the Grid State by calling Grid.SetState(null). This doesn't reset ColumnState<T>.Locked boolean to false and the columns remain locked.

---

ADMIN EDIT

---

A possible workaround for the time being is to additionally loop through the ColumnStates collection of the State and set the Locked property to false for each column.

Example: https://blazorrepl.telerik.com/QTYmkpvb49c6CPxa42

The problem with the extra characters at the beginning of the PDF document has resurfaced.

The bytes returned by GetFileAsync() don't start with %PDF-, but with JS.ReceiveByteArray. Some PDF readers and my antivirus flag the file as corrupt or suspicious. I worked around it by stripping everything before the first %PDF- occurrence in the bytes before writing to disk.

I use TelerikPdfViewer to let my users annotate PDF documents (highlights, text boxes, drawings). Since the component only provides a built-in Download button (client-side) and not a Save to backend, I implemented a custom Save button that:

1. Calls await pdfViewerRef.GetFileAsync() to retrieve th e annotated PDF as byte[].
2. Sends the bytes to my server via a Blazor service call.
3. The server persists them to a file share with File.WriteAllBytesAsync(path, bytes).

Simplified:

<PdfViewerToolBarCustomTool>
    <TelerikButton OnClick="@SaveAnnotationsAsync">Save</TelerikButton>
</PdfViewerToolBarCustomTool>

var annotatedPdf = await pdfViewerRef.GetFileAsync();
await _scanFlowApi.SaveAnnotatedDocumentAsync(documentId, annotatedPdf);
// server-side: await File.WriteAllBytesAsync(path, annotatedPdf, ct);

It works — the annotations are saved and I can reopen the file in the viewer without issues. But after saving and opening the file in Adobe Reader, closing it shows the prompt "Do you want to save the changes made to this document?" — even though the user hasn't modified anything in Adobe. The PDF seems to contain incremental updates appended at the end.

The PDF standard allows two ways to configure Acro fields and relate them to inputs (widget annotations):

1. The field can be independent of the input widget. There can even be multiple inputs that point to the same field.
2. The field and the widget can be represented by the same object in the PDF file.

Adobe Acrobat supports both options. Telerik PdfProcessing supports only the first option, which is more commonly used. The PDF Viewer supports only the second option. If the PDF Viewer loads a file with the first configuration, the component saves new field values in such a way that they can't be retrieved by PdfProcessing. Moreover, if the PDF file is opened locally, it looks like the new values are there, but when you click on a field, the original value shows. The new value behaves like a placeholder rather than a real value.

To Reproduce

1. Open a file with Acro fields in the PDF Viewer with enabled form filling
2. Edit the fields and save the file.
3. Open the file with a desktop client like Adobe Acrobat Reader.
4. Click on a textbox.
5. Result - the old value shows. Instead, the new value should persist.
   

With an active Blazor trial, the Telerik Document Processing NuGet packages are not found in the Visual Studio Package Manager and in the Terminal as well:

Telerik input components inside EditorTemplate render the whole grid on each keystroke

<AdminEdit>

As a workaround, you can use the standard Input components provided by the framework together with a CSS class that would visually make them like the Telerik Input Components. An example for the TextArea:

<InputTextArea class="k-textarea" @bind-Value="@myValue"></InputTextArea>

</AdminEdit>

With `PersistTabContent="true"`, when tabs start with `Visible="false"` and later become `Visible="true"`, all visible tab contents are instantiated simultaneously instead of only the active tab.

Reproduction: 

@page "/TestPage"

<button @onclick="Load">Load</button>

<TelerikTabStrip PersistTabContent="true">
    <TabStripTab Title="Tab 1" Visible="@_tabsVisible">
        <TestInitComponent Message="Hello from tab1" />
    </TabStripTab>
    <TabStripTab Title="Tab 2" Visible="@_tabsVisible">
        <TestInitComponent Message="Hello from tab2" />
    </TabStripTab>
    <TabStripTab Title="Tab 3" Visible="@_tabsVisible">
        <TestInitComponent Message="Hello from tab3" />
    </TabStripTab>
</TelerikTabStrip>

@code {
    private bool _tabsVisible = false;

    private void Load()
    {
        _tabsVisible = true;
    }
}

TestInitComponent.razor

<h3>TestInitComponent</h3>

@code {

    [Parameter]
    public string Message { get; set; } = string.Empty;

    protected override void OnInitialized()
    {
        base.OnInitialized();
        Console.WriteLine($"TestInitComponent OnInitialized {Message}");
    }
}

Steps: Open page → click Load.

The appointments at the start of the day seem accurate. If you scroll down, the position of the appointments does not line up with the grid line for the hour that it starts at or ends at. The issue can be observed in the live demo.

The Grid performance worsens progressively with each subsequent edit operation. Please optimize that.

Test page: https://blazorrepl.telerik.com/mJuHFNbb17FpJu9b54

Click on a Price or Quantity cell to start edit mode and tab repetitively to observe the degradation.

Hi Support,

I have an issue with the DragToSelect feature of a Telerik grid in Blazor when this grid is inside a TelerikWindow. 

Summary
When a TelerikGrid configured with GridSelectionSettings DragToSelect="true" is rendered inside the <WindowContent> of a <TelerikWindow>, the drag-to-select (rubber-band) behavior is not working properly — the user can only select cells/rows via individual clicks.

Single-click selection continues to work in both cases. The issue is specific to the drag gesture.

Steps to reproduce
Create a page with a TelerikWindow set to Visible="true".
Inside <WindowContent>, place a TelerikGrid with:
SelectionMode="@GridSelectionMode.Multiple"
SelectedCells / SelectedCellsChanged bound
<GridSettings><GridSelectionSettings SelectionType="@GridSelectionType.Cell" DragToSelect="true" /></GridSettings>
Open the window and try to select multiple cells by pressing the mouse button on a cell and dragging over neighboring cells.

Expected behavior
A rubber-band selection rectangle appears and all cells the pointer passes over become selected — same as when the identical grid is placed on a regular page (outside a modal window).

Actual behavior
Drag selection occur rarely. Only the single cell under the initial mousedown gets selected. The rubber-band rectangle rarely appears, and SelectedCellsChanged fires with a single descriptor instead of the full drag range.

Minimal repro (REPL-ready)
<TelerikWindow Visible="true" Width="800px" Height="500px">
    <WindowTitle>Repro</WindowTitle>
    <WindowContent>
        <TelerikGrid Data="@Data" TItem="SampleItem"
                     SelectionMode="@GridSelectionMode.Multiple"
                     SelectedCells="@SelectedCells"
                     SelectedCellsChanged="@((IEnumerable<GridSelectedCellDescriptor> c) => SelectedCells = c)">
            <GridSettings>
                <GridSelectionSettings SelectionType="@GridSelectionType.Cell" DragToSelect="true" />
            </GridSettings>
            <GridColumns>
                <GridColumn Field="@nameof(SampleItem.Id)" />
                <GridColumn Field="@nameof(SampleItem.Name)" />
            </GridColumns>
        </TelerikGrid>
    </WindowContent>
</TelerikWindow>

@code {
    public record SampleItem(int Id, string Name);
    private List<SampleItem> Data = Enumerable.Range(1, 20).Select(i => new SampleItem(i, $"Item {i}")).ToList();
    private IEnumerable<GridSelectedCellDescriptor> SelectedCells = Enumerable.Empty<GridSelectedCellDescriptor>();
}

Now my questions :
- Is this a known limitation of DragToSelect when the grid is inside a modal TelerikWindow?
- Is there an officially supported workaround (CSS pointer-events tweak on .k-overlay, event capture override, grid setting, etc.)?
- If it is a bug, could you open a public issue we can track?

Many thanks you in advance.

Franck Boisdé

Hello,

I see this often when running your Product updater, or it may come from within VS 2026 when it prompts to update projects. I had Telerik UI for Blazor 13.2 installed, updated using the product updater and got the prompt for the project updater and now 13.3.0 is active. The problem though is when you add a new version entry in the nuget package sources the older version(s) are not being removed. This breaks the build, it will fail to restore packages, etc. 

Bug report

Reproduction of the problem

(bug report only)
Regression introduced in 13.0.0.
1. Run this example: https://blazorrepl.telerik.com/wUuSGClv00orFeRm59

Current behavior

(optional)
The Size, Rounded, FillMode parameters are ignored.

Expected/desired behavior

The parameter values should apply and change the appearance of the SearchBox.

Environment

• Browser: [all ]

When SchedulerGroupOrientation is set to vertical, increasing the height of the `SchedulerResourceGroupHeader` breaks the rendering of the Scheduler cells, which causes misalignment of the appointments. In my scenario, I want to have a Button and an Icon in the group header cell.

Reproduction example: https://blazorrepl.telerik.com/wJElGYvF02XSsN6j42

The value in a numeric textbox cannot be changed for negative numerbes unless you erase all the text and restart.

(Also applies to AutoComplete, DropDownList, MultiSelect, MultiColumnComboBox).

When using Height="auto" in the popup settings and filtering with a dropdown above the component, the dropdown detaches from the main component.

<ComboBoxPopupSettings Height="auto"></ComboBoxPopupSettings>

https://blazorrepl.telerik.com/cKkSQGFO50ovCpr829

A possible workaround is to use a MaxHeight that is less than half the browser viewport.

<ComboBoxPopupSettings Height="auto" MaxHeight="45vh"></ComboBoxPopupSettings>

Description

File data is not available in the Upload's OnSuccess event.

Regression in version 9.0.0 introduced with the addition of the chunk upload functionality.

https://github.com/telerik/blazor/blob/master/js/telerik-blazor/src/upload/upload.ts#L282-L288

Steps To Reproduce

1. Attach a handler to the OnSuccess event:

<TelerikUpload SaveUrl="/api/upload/save"
               RemoveUrl="/api/upload/remove"
               OnSuccess="@OnSuccessHandler" />

@code {
    async Task OnSuccessHandler(UploadSuccessEventArgs e)
    {
        foreach (var file in e.Files)
        {
            Console.WriteLine($"Name = {file.Name}, Size = {file.Size}, Extension = {file.Extension}");
        }

        StateHasChanged();
    }
}

2. Upload a file and try to access its Name, Size, and Extension properties in the event handler.

Actual Behavior

The properties have their default values (null for Name and Extension and 0 for Size).

Expected Behavior

The actual file data is accessible in the OnSuccess event handler.

Browser

All

Last working version of Telerik UI for Blazor (if regression)

8.1.1