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Problem with TelerikComboBox and NullReferenceException

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ComboBox
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web
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web asked on 23 Mar 2020, 05:29 PM

Hello,

I have setup a ServerSide Blazor Project. I have tried many different options by i always get NullReferenceException.

My Blazor html

 

<TelerikComboBox Data="@ProductsList" Value="@Filters.ProductId"
                                         Placeholder="Επιλογή Project"
                                         TextField="Title"
                                         ValueField="Id"
                                         Id="CbProject"
                                         ValueChanged="@( (System.Guid? id) => ProjectSelected2(id) )">
                        </TelerikComboBox>

 

My exception

NullReferenceException: Object reference not set to an instance of an object.
Telerik.Blazor.Components.RootComponent.TelerikRootComponentFragmentBase.Dispose()
Microsoft.AspNetCore.Components.Rendering.ComponentState.Dispose()
Microsoft.AspNetCore.Components.RenderTree.Renderer.Dispose(bool disposing)
Microsoft.AspNetCore.Components.Rendering.HtmlRenderer.HandleException(Exception exception)
Microsoft.AspNetCore.Components.RenderTree.Renderer.Dispose(bool disposing)
Microsoft.AspNetCore.Components.RenderTree.Renderer.Dispose()
Microsoft.AspNetCore.Mvc.ViewFeatures.StaticComponentRenderer.PrerenderComponentAsync(ParameterView parameters, HttpContext httpContext, Type componentType)
Microsoft.AspNetCore.Mvc.ViewFeatures.ComponentRenderer.PrerenderedServerComponentAsync(HttpContext context, ServerComponentInvocationSequence invocationId, Type type, ParameterView parametersCollection)
Microsoft.AspNetCore.Mvc.ViewFeatures.ComponentRenderer.RenderComponentAsync(ViewContext viewContext, Type componentType, RenderMode renderMode, object parameters)
Microsoft.AspNetCore.Mvc.TagHelpers.ComponentTagHelper.ProcessAsync(TagHelperContext context, TagHelperOutput output)
Microsoft.AspNetCore.Razor.Runtime.TagHelpers.TagHelperRunner.<RunAsync>g__Awaited|0_0(Task task, TagHelperExecutionContext executionContext, int i, int count)
AspNetCore.Views__Blazor_Index.ExecuteAsync() in Index.cshtml
+
<component type="typeof(CenterConsole.Blazor.Pages.App)" render-mode="ServerPrerendered" />

Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderPageCoreAsync(IRazorPage page, ViewContext context)
Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderPageAsync(IRazorPage page, ViewContext context, bool invokeViewStarts)
Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderAsync(ViewContext context)
Microsoft.AspNetCore.Mvc.ViewFeatures.ViewExecutor.ExecuteAsync(ViewContext viewContext, string contentType, Nullable<int> statusCode)
Microsoft.AspNetCore.Mvc.ViewFeatures.ViewExecutor.ExecuteAsync(ViewContext viewContext, string contentType, Nullable<int> statusCode)
Microsoft.AspNetCore.Mvc.ViewFeatures.ViewExecutor.ExecuteAsync(ActionContext actionContext, IView view, ViewDataDictionary viewData, ITempDataDictionary tempData, string contentType, Nullable<int> statusCode)
Microsoft.AspNetCore.Mvc.ViewFeatures.ViewResultExecutor.ExecuteAsync(ActionContext context, ViewResult result)
Microsoft.AspNetCore.Mvc.ViewResult.ExecuteResultAsync(ActionContext context)
Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeResultAsync>g__Logged|21_0(ResourceInvoker invoker, IActionResult result)
Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResultFilterAsync>g__Awaited|29_0<TFilter, TFilterAsync>(ResourceInvoker invoker, Task lastTask, State next, Scope scope, object state, bool isCompleted)
Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResultExecutedContextSealed context)
Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.ResultNext<TFilter, TFilterAsync>(ref State next, ref Scope scope, ref object state, ref bool isCompleted)
Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeResultFilters>g__Awaited|27_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, object state, bool isCompleted)
Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResourceFilter>g__Awaited|24_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, object state, bool isCompleted)
Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResourceExecutedContextSealed context)
Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Next(ref State next, ref Scope scope, ref object state, ref bool isCompleted)
Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeFilterPipelineAsync>g__Awaited|19_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, object state, bool isCompleted)
Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Logged|17_1(ResourceInvoker invoker)
Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger)

....

.

2 Answers, 1 is accepted

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web
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answered on 23 Mar 2020, 05:32 PM
I don't know what to investigate next, please give some hint.
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Marin Bratanov
Telerik team
answered on 24 Mar 2020, 08:34 AM

Hi,

This indicates that the TelerikRootComponent is missing. You can read more about it here: https://docs.telerik.com/blazor-ui/getting-started/what-you-need#project-configuration.

From the stack trace it seems you are using Razor components that use our components in an MVC app, so I suggest you review this example, its readme file and code comments on this scenario: https://github.com/telerik/blazor-ui/tree/master/common/razor-components. The key thing is that you need to have the TelerikRootComponent in each individual razor component because they are scoped and cannot find instances higher in the hierarchy.

 

Regards,
Marin Bratanov
Progress Telerik

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Marin Bratanov
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