Questions on UI for Blazor Forum

1 answer

38 views

[Solved] No OnUpdate event after Dropdown value changes in TelerikGrid having GridEditMode.incell

Given this markup:

<TelerikGrid Data="@PrognoseData" EditMode="GridEditMode.Incell" OnUpdate="@OnGridUpdate">
	<GridColumns>
		<GridColumn Title="Prijs/eenh." Field="PrognoseKostenModel.EenheidId" Width="120px">
			<EditorTemplate>
      @{
        var model = (PrognoseKostenModel)context;
        <TelerikDropDownList Data="@_eenheden" 
                             @bind-Value="@model.EenheidId" 
                             TextField="@nameof(PrijsEenheidDto.Sign)" 
                             ValueField="@nameof(PrijsEenheidDto.Id)" >
					<DropDownListSettings>
						<DropDownListPopupSettings Height="auto"/>
					</DropDownListSettings>
				</TelerikDropDownList>
      }
      </EditorTemplate>
			<Template>
        @{
          var model = (PrognoseKostenModel)context;
        }

          <span>@model.Eenheid</span>
      </Template>
		</GridColumn>
	</GridColumns>
</TelerikGrid>

So eg:

1. the initial value is "vkm2"
2. User selects "post" in dropdown
3. Dropdown is automatically closed, but value in grid remains "vkm2"
4. User clicks in different field in same row: OnGridUpdate is fired and value in grid changes to "post"

Any idea how to get OnGridUpdate immediately after the selection in the dropdown?

DropDownList

Grid

answered on 17 Apr 2026

1 answer

37 views

[Solved] FormItem template invalidation state for custom DropDownList component

Hy,

I have an issue with the validation state of a FormItem that uses a custom Template.

I have created the following TelerikForm:

MyForm.razor

DepartmentSelect.razor

LineInefficientyRegistryDto.cs

According with the link Blazor Form Form Items Template - Telerik UI for Blazor, I expect to obtain the following result when the field is not valid after the form submit:

But I have this:

As you can see, the DropDownList is not being highlighted in red.

Does anyone know why this happens and how to resolve the issue?

Regards,

Marco

DropDownList

Form

answered on 05 Mar 2026

0 answers

104 views

issue where the prefilled AutoComplete value was cleared on initial focus-out on after page initialization

combobox issue in blazor

ComboBox

DropDownList

TextBox

updated question on 09 Jan 2026

1 answer

241 views

Add a filter option to the dropdownlists for the fields within the filter component

Hi, we are using the filter component extensively and our model has a large number of fields. It is cumbersome locating the correct field to filter on from the drop down list. Is it possible to add a filter to the field drop down as shown below the same as what is available when using filterable = true on a drop down list?

.

DropDownList

Filter

answered on 25 Dec 2025

1 answer

125 views

ComboBox and DropDownList Options all start with weird character.

I've followed everything i can find about enforcing UTF-8 encoding, but this is still happening. It only happens in the drop down options of the aforementioned components, not after they are selected and not in the ASP.NET core <InputSelect> component.

ComboBox

DropDownList

updated answer on 13 Nov 2025

1 answer

69 views

Missing Open method for TelerikDropDownButton

The Dropdownlist has an Open method to open it programatically, the DropdownButton has no such functionality.

DropDownButton

DropDownList

answered on 30 Oct 2025

1 answer

61 views

DropdownList, OnRead, Grouping

Hi there

I'm trying to use DropDownlist with the Grouping field and the OnReadEvent, with mode = DropDownScrollMode.Scrollable

The OnRead event provides the grouping field to the request. The request is sent to my (API) server that handles the request, and the result is returned . Then after my OnReadHandler method ands, I get an internal exception: "System.NullReferenceException: 'Object reference not set to an instance of an object.'"

with following stack:

 	Telerik.Blazor.dll!Telerik.Blazor.Components.Common.TelerikSelectBase<SNG.LccNion.API.Model.Dto.IDDescriptiveDto, string>.ProcessGroupData(System.Collections.IEnumerable data)	Unknown
 	Telerik.Blazor.dll!Telerik.Blazor.Components.Common.TelerikSelectBase<SNG.LccNion.API.Model.Dto.IDDescriptiveDto, string>.SetProcessedData(System.Collections.IEnumerable data)	Unknown
 	Telerik.Blazor.dll!Telerik.Blazor.Components.TelerikDropDownList<SNG.LccNion.API.Model.Dto.IDDescriptiveDto, string>.SetProcessedData(System.Collections.IEnumerable data)	Unknown
 	Telerik.Blazor.dll!Telerik.Blazor.Components.Common.DataBoundComponent<SNG.LccNion.API.Model.Dto.IDDescriptiveDto>.ProcessOnReadResult(Telerik.Blazor.Components.ReadEventArgs args)	Unknown
 	Telerik.Blazor.dll!Telerik.Blazor.Components.Common.TelerikSelectBase<SNG.LccNion.API.Model.Dto.IDDescriptiveDto, string>.ProcessOnReadResult(Telerik.Blazor.Components.ReadEventArgs args)	Unknown
 	Telerik.Blazor.dll!Telerik.Blazor.Components.Common.DataBoundComponent<SNG.LccNion.API.Model.Dto.IDDescriptiveDto>.ProcessOnReadData()	Unknown
 	[Resuming Async Method]	
>	System.Private.CoreLib.dll!System.Runtime.CompilerServices.AsyncTaskMethodBuilder<System.Threading.Tasks.VoidTaskResult>.AsyncStateMachineBox<Telerik.Blazor.Components.Common.DataBoundComponent<SNG.LccNion.API.Model.Dto.IDDescriptiveDto>.<ProcessOnReadData>d__39>.ExecutionContextCallback(object s) Line 292	C#
 	System.Private.CoreLib.dll!System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state) Line 179	C#
 	System.Private.CoreLib.dll!System.Runtime.CompilerServices.AsyncTaskMethodBuilder<System.Threading.Tasks.VoidTaskResult>.AsyncStateMachineBox<Telerik.Blazor.Components.Common.DataBoundComponent<SNG.LccNion.API.Model.Dto.IDDescriptiveDto>.<ProcessOnReadData>d__39>.MoveNext(System.Threading.Thread threadPoolThread) Line 372	C#
 	System.Private.CoreLib.dll!System.Runtime.CompilerServices.AsyncTaskMethodBuilder<System.Threading.Tasks.VoidTaskResult>.AsyncStateMachineBox<Telerik.Blazor.Components.Common.DataBoundComponent<System.__Canon>.<ProcessOnReadData>d__39>.MoveNext() Line 350	C#
 	System.Private.CoreLib.dll!System.Runtime.CompilerServices.TaskAwaiter.OutputWaitEtwEvents.AnonymousMethod__12_0(System.Action innerContinuation, System.Threading.Tasks.Task innerTask) Line 281	C#
 	System.Private.CoreLib.dll!System.Threading.Tasks.AwaitTaskContinuation.RunCallback(System.Threading.ContextCallback callback, object state, ref System.Threading.Tasks.Task currentTask) Line 697	C#
 	System.Private.CoreLib.dll!System.Threading.Tasks.Task.RunContinuations(object continuationObject) Line 3486	C#
 	System.Private.CoreLib.dll!System.Runtime.CompilerServices.AsyncTaskMethodBuilder<Telerik.Blazor.Components.ReadEventArgs>.SetResult(Telerik.Blazor.Components.ReadEventArgs result) Line 478	C#
 	[Completed] Telerik.Blazor.dll!Telerik.Blazor.Components.TelerikDropDownList<SNG.LccNion.API.Model.Dto.IDDescriptiveDto, string>.TriggerReadAsync(Telerik.DataSource.DataSourceRequest request)	Unknown

I am struggling to handle the request correctly and provide an answer back to the list that it can handle properly.

Nevertheless I get errors. Is there a working example of using the OnRead event with the GroupField property set to a property of the TItem? Or is this combination impossible inspite of DropDownScrollMode.Scrollable mode?

BTW - In case of large dropdownlist result set I want to fall back to virtual mode, and drop the grouping option, as it is documented that these are not compatible. (This is handled blazor side by checking the dataset count before the first OnRead call)

DropDownList

answered on 30 Oct 2025

1 answer

187 views

[Solved] How to control visual layout of DropDownListPopupSettings ... list of the .k class selectors?

I've tried to find documentation on how to modify the CSS for the dropdownlist and it's popup but can't seem to figure out how to change the "Search" area size, nor the "Select Type" (they are too large).

I was able to figure out how to adjust the actual items:

.custom-compact-dropdownlist-popup .k-list-item {
    padding-top: 2px;
    padding-bottom: 2px;
    font-size: 0.90em;
}

and reference:

<DropDownListSettings>
    <DropDownListPopupSettings Class="custom-compact-dropdownlist-popup" />

but I don't know what to use in CSS ... is there a list somewhere of the ".k" class selectors?

Rob.

DropDownList

answered on 27 Oct 2025

0 answers

110 views

TypeError: Cannot read properties of null (reading 'addEventListener')

I have this javascript exception when use MultiColumnComboBox (but sometime also with ComboBox / DropDown).

If i continue debugging it go without issue, but it break always on component load.

ComboBox

DropDownList

MultiColumnComboBox

asked on 18 Jun 2025

1 answer

162 views

[Solved] How to change DropDownList Size?

I'm trying to adjust the existing size definitions as outlined here in your docs:

https://www.telerik.com/blazor-ui/documentation/components/dropdownlist/appearance

I'd like to adjust the definition for sm, md, lg as they don't work well with TailwindCSS settings. For example lg is just a tad too large and md is a tad too small

This is lg:

This md:

I want to match the border size to our standard input text (aka Postal Code example above). I can't seem to find where sm, lg, md are defined? And, is there a relative "simple" way to modify without going down a "custom" theme path?

Rob.

DropDownList

answered on 10 Jun 2025