Blazor - ClosedXml - excel cannot open the file beacause the file format or extension is not valid

Question

I'm attempting to export some information from my Blazor page to an Excel workbook. However, I receive the following error message when I attempt to access the file:

excel cannot open the file because the file format or extension is not valid

When I open the file in notepad++ I get see a bunch of letters and signs but no valid data.

My code:

 public byte[] SaveSearchToExcel(List<EquipmentForm> EquipmentForms)
    {
        var wb = new XLWorkbook();
  

        var ws = wb.Worksheets.Add("Search Results");
        ws.Cell(1, 1).Value = "TLV Number";
        ws.Cell(1, 2).Value = "Descirption";
        for(int row = 0; row < EquipmentForms.Count; row++)
        {
            ws.Cell(row + 1, 1).Value = EquipmentForms[row].TLVNumber;
            ws.Cell(row+1, 2).Value = EquipmentForms[row].Description;
        }



        MemoryStream XLSStream = new();
        wb.SaveAs(XLSStream);
        XLSStream.Position = 0;
        return XLSStream.ToArray();

    }

  private async void SaveToExcel(){
    var XLSStream= _saveToExcel.SaveSearchToExcel(EquipmentForms);
    
    await js.InvokeVoidAsync("BlazorDownloadFile", "export.xlsx",Convert.ToBase64String(XLSStream));

    }

function BlazorDownloadFile(filename, content) {
// thanks to Geral Barre : https://www.meziantou.net/generating-and-downloading-a-file-in-a-blazor-webassembly-application.htm 

// Create the URL
const file = new File([content], filename, { type: "application/octet-stream" });
const exportUrl = URL.createObjectURL(file);

// Create the <a> element and click on it
const a = document.createElement("a");
document.body.appendChild(a);
a.href = exportUrl;
a.download = filename;
a.target = "_self";
a.click();

// We don't need to keep the object url, let's release the memory
// On Safari it seems you need to comment this line... (please let me know if you know why)
URL.revokeObjectURL(exportUrl);

}

What I'm doing wrong here?

narikkadan · Answer 1 · Jan 20, 2023

Changed the following code:

function BlazorDownloadFile(filename, bytesBase64) {
var link = document.createElement('a');
link.download = filename;
link.href = "data:application/octet-stream;base64," + bytesBase64;
document.body.appendChild(link); // Needed for Firefox
link.click();
document.body.removeChild(link);