ASP.NET Excel Viewer

@model List<SheetModel>
@{
  ViewData["Title"] = "ASP.NET Excel Viewer Demo";
}

<div class="text-center">
  <h1 class="display-4">1. Upload Excel File</h1>
  @using (Html.BeginForm("UploadFile", "Home", FormMethod.Post, new { enctype = "multipart/form-data" }))
  {
    <input type="file" name="file" accept=".xlsx,.xls,.ods,.csv,.txt,.xlsm,.xltx,.xltm,.html,.mhtml" />
    <input type="submit" value="Display" />
  }
  <h1 class="display-4">2. Display Excel File</h1>
  @if (Model.Count > 0)
  {
    <ul class="nav nav-tabs" id="myTab" role="tablist">
      @for (int i = 0; i < Model.Count; i++)
      {
        <li class="nav-item">
          <a @Html.Raw(i == 0 ? "class='nav-link active'" : "class='nav-link'") id="@("tab"+i)" data-toggle="tab" href="@("#tabpanel"+i)" role="tab" aria-controls="@("tabpanel" + i)" aria-selected="@(i==0)">
            @Model[i].SheetName
          </a>
        </li>
      }
    </ul>
    <div class="tab-content" id="myTabContent">
      @for (int i = 0; i < Model.Count; i++)
      {
        <div @Html.Raw(i == 0 ? "class='tab-pane fade show active'" : "class='tab-pane fade'") id="@("tabpanel" + i)" role="tabpanel" aria-labelledby="@("tab"+i)">
          @if (Model[i].HasContent)
          {
            <img src="@Url.Action("ShowImage", "Home", new { index = i })" class="float-left mt-4" />
          }
        </div>
      }
    </div>
  }
  else
  {
    <p>Please upload your file and click on Display!</p>
  }
</div>

using AspNetExcelViewer.Models;
using GemBox.Spreadsheet;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Logging;
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;

public class HomeController : Controller
{
    private readonly ILogger<HomeController> _logger;

    static HomeController()
    {
        // If you are using the Professional version, enter your serial key below.
        SpreadsheetInfo.SetLicense("FREE-LIMITED-KEY");
    }

    public HomeController(ILogger<HomeController> logger)
    {
        _logger = logger;
    }

    public IActionResult Index()
    {
        List<SheetModel> sheets = new List<SheetModel>();
        int? sheetCount = HttpContext.Session.GetInt32("ExcelFileSheetCount");
        if (sheetCount.HasValue)
        {
            for (int i = 0; i < sheetCount.Value; i++)
            {
                sheets.Add(new SheetModel(
                    HttpContext.Session.GetString("ExcelFileSheetName" + i), 
                    HttpContext.Session.Get("ExcelFileSheetImage" + i) != null));
            }
        }

        return View(sheets);
    }

    // Read stored image from the Session
    public ActionResult ShowImage(int index)
    {
        byte[] image = HttpContext.Session.Get("ExcelFileSheetImage" + index);
        return new FileStreamResult(new MemoryStream(image), "image/png");
    }

    [HttpPost]
    public ActionResult UploadFile(IFormFile file)
    {
        // Load excel file that you have uploaded
        ExcelFile ef = ExcelFile.Load(file.OpenReadStream());

        // Use Session to store file properties required for displaying it on the page
        HttpContext.Session.SetInt32("ExcelFileSheetCount", ef.Worksheets.Count);

        for (int i = 0; i < ef.Worksheets.Count; i++)
        {
            ExcelWorksheet sheet = ef.Worksheets[i];

            HttpContext.Session.SetString("ExcelFileSheetName" + i, sheet.Name);

            // Print options will be used when exporting sheets to images
            sheet.PrintOptions.FitWorksheetHeightToPages = 1;
            sheet.PrintOptions.FitWorksheetWidthToPages = 1;
            sheet.PrintOptions.PrintGridlines = sheet.ViewOptions.ShowGridLines;
            sheet.PrintOptions.PrintHeadings = true;

            // Export active sheet to an image
            ef.Worksheets.ActiveWorksheet = sheet;

            Tuple<double, double> pageSize = GetSheetSize(sheet);
            if (pageSize.Item1 == 0 || pageSize.Item2 == 0)
                continue;

            using (MemoryStream imageStream = new MemoryStream())
            {
                ImageSaveOptions options = new ImageSaveOptions()
                {
                    Format = ImageSaveFormat.Png,
                    Width = pageSize.Item1,
                    Height = pageSize.Item2,
                    CropToContent = true
                };
                ef.Save(imageStream, options);

                HttpContext.Session.Set("ExcelFileSheetImage" + i, imageStream.ToArray());
            }
        }

        return RedirectToAction("Index");
    }

    private static Tuple<double, double> GetSheetSize(ExcelWorksheet sheet)
    {
        CellRange usedCellRange = sheet.GetUsedCellRange(true);
        if (usedCellRange == null)
            return Tuple.Create(0d, 0d);

        double width = 0, height = 0;
        for (int i = 0; i <= usedCellRange.LastColumnIndex; i++)
        {
            width += sheet.Columns[i].GetWidth(LengthUnit.Pixel);
        }

        for (int i = 0; i <= usedCellRange.LastRowIndex; i++)
        {
            height += sheet.Rows[i].GetHeight(LengthUnit.Pixel);
        }

        return Tuple.Create(width, height);
    }
}

public class SheetModel
{
    public string SheetName { get; private set; }
    public bool HasContent { get; private set; }

    public SheetModel(string sheetName, bool hasContent)
    {
        this.SheetName = sheetName;
        this.HasContent = hasContent;
    }
}