Last Updated: 06 Jul 2021 09:46 by ADMIN
Created on: 01 Jul 2021 17:29
Category: SpreadProcessing
Type: Bug Report
Blazor Web Assembly: Importing XLSX file (from MemoryStream) very slow

Importing XLSX file in Blazor Web Assembly for .NET 5.0 is very slow.


          <InputFile OnChange="@HandleFileSelected" />


async Task HandleFileSelected(InputFileChangeEventArgs e)


   var ms = new MemoryStream((int)e.File.Size);
        Telerik.Windows.Documents.Spreadsheet.FormatProviders.OpenXml.Xlsx.XlsxFormatProvider formatProvider = new Telerik.Windows.Documents.Spreadsheet.FormatProviders.OpenXml.Xlsx.XlsxFormatProvider();
        using (Stream ey = e.File.OpenReadStream(e.File.Size))
            await ey.CopyToAsync(ms,(int)e.File.Size);
        oWorkbook = formatProvider.Import(ms);


1 comment
Posted on: 06 Jul 2021 09:46

Hello Michael,

Importing data in Blazor WASM is a very slow operation that will take a long time in the framework due to the many smaller operations that need to be performed internally to parse the content. I highly recommend you send to the client only what it needs at the moment and perform the data operations on the server as this will provide you with a much better performance.

I also advise you to review the Slow Performance section of our documentation for more tips and ideas on improving your app's performance:

Hope this is helpful.

Progress Telerik

Virtual Classroom, the free self-paced technical training that gets you up to speed with Telerik and Kendo UI products quickly just got a fresh new look + new and improved content including a brand new Blazor course! Check it out at