Excel to DataTable using EPPlus - excel locked for editing

A extension version of Tim Schmelter's answer.

public static DataTable ToDataTable(this ExcelWorksheet ws, bool hasHeaderRow = true)
{
    var tbl = new DataTable();
    foreach (var firstRowCell in ws.Cells[1, 1, 1, ws.Dimension.End.Column])
        tbl.Columns.Add(hasHeaderRow ?
            firstRowCell.Text : string.Format("Column {0}", firstRowCell.Start.Column));
    var startRow = hasHeaderRow ? 2 : 1;
    for (var rowNum = startRow; rowNum <= ws.Dimension.End.Row; rowNum++)
    {
        var wsRow = ws.Cells[rowNum, 1, rowNum, ws.Dimension.End.Column];
        var row = tbl.NewRow();
        foreach (var cell in wsRow) row[cell.Start.Column - 1] = cell.Text;
        tbl.Rows.Add(row);
    }
    return tbl;
}

I see, that's what i've posted recently here(now corrected). It can be improved since the ExcelPackage and the FileStream(from File.OpenRead) are not disposed after using.

public static DataTable GetDataTableFromExcel(string path, bool hasHeader = true)
{
    using (var pck = new OfficeOpenXml.ExcelPackage())
    {
        using (var stream = File.OpenRead(path))
        {
            pck.Load(stream);
        }
        var ws = pck.Workbook.Worksheets.First();  
        DataTable tbl = new DataTable();
        foreach (var firstRowCell in ws.Cells[1, 1, 1, ws.Dimension.End.Column])
        {
            tbl.Columns.Add(hasHeader ? firstRowCell.Text : string.Format("Column {0}", firstRowCell.Start.Column));
        }
        var startRow = hasHeader ? 2 : 1;
        for (int rowNum = startRow; rowNum <= ws.Dimension.End.Row; rowNum++)
        {
            var wsRow = ws.Cells[rowNum, 1, rowNum, ws.Dimension.End.Column];
            DataRow row = tbl.Rows.Add();
            foreach (var cell in wsRow)
            {
                row[cell.Start.Column - 1] = cell.Text;
            }
        }
        return tbl;
    }
}

I've created a method that converts an Excel file to a DataTable using EPPlus, and tried to maintain Type Safety. Also duplicate column names are handled and with a boolean you can tell the method wether the sheet has a row with headers. I've created it for a complex import process that has several steps after uploading that requires user input before committing to the database.

private DataTable ExcelToDataTable(byte[] excelDocumentAsBytes, bool hasHeaderRow)
{
    DataTable dt = new DataTable();
    string errorMessages = "";

    //create a new Excel package in a memorystream
    using (MemoryStream stream = new MemoryStream(excelDocumentAsBytes))
    using (ExcelPackage excelPackage = new ExcelPackage(stream))
    {
        ExcelWorksheet worksheet = excelPackage.Workbook.Worksheets[1];

        //check if the worksheet is completely empty
        if (worksheet.Dimension == null)
        {
            return dt;
        }

        //add the columns to the datatable
        for (int j = worksheet.Dimension.Start.Column; j <= worksheet.Dimension.End.Column; j++)
        {
            string columnName = "Column " + j;
            var excelCell = worksheet.Cells[1, j].Value;

            if (excelCell != null)
            {
                var excelCellDataType = excelCell;

                //if there is a headerrow, set the next cell for the datatype and set the column name
                if (hasHeaderRow == true)
                {
                    excelCellDataType = worksheet.Cells[2, j].Value;

                    columnName = excelCell.ToString();

                    //check if the column name already exists in the datatable, if so make a unique name
                    if (dt.Columns.Contains(columnName) == true)
                    {
                        columnName = columnName + "_" + j;
                    }
                }

                //try to determine the datatype for the column (by looking at the next column if there is a header row)
                if (excelCellDataType is DateTime)
                {
                    dt.Columns.Add(columnName, typeof(DateTime));
                }
                else if (excelCellDataType is Boolean)
                {
                    dt.Columns.Add(columnName, typeof(Boolean));
                }
                else if (excelCellDataType is Double)
                {
                    //determine if the value is a decimal or int by looking for a decimal separator
                    //not the cleanest of solutions but it works since excel always gives a double
                    if (excelCellDataType.ToString().Contains(".") || excelCellDataType.ToString().Contains(","))
                    {
                        dt.Columns.Add(columnName, typeof(Decimal));
                    }
                    else
                    {
                        dt.Columns.Add(columnName, typeof(Int64));
                    }
                }
                else
                {
                    dt.Columns.Add(columnName, typeof(String));
                }
            }
            else
            {
                dt.Columns.Add(columnName, typeof(String));
            }
        }

        //start adding data the datatable here by looping all rows and columns
        for (int i = worksheet.Dimension.Start.Row + Convert.ToInt32(hasHeaderRow); i <= worksheet.Dimension.End.Row; i++)
        {
            //create a new datatable row
            DataRow row = dt.NewRow();

            //loop all columns
            for (int j = worksheet.Dimension.Start.Column; j <= worksheet.Dimension.End.Column; j++)
            {
                var excelCell = worksheet.Cells[i, j].Value;

                //add cell value to the datatable
                if (excelCell != null)
                {
                    try
                    {
                        row[j - 1] = excelCell;
                    }
                    catch
                    {
                        errorMessages += "Row " + (i - 1) + ", Column " + j + ". Invalid " + dt.Columns[j - 1].DataType.ToString().Replace("System.", "") + " value:  " + excelCell.ToString() + "<br>";
                    }
                }
            }

            //add the new row to the datatable
            dt.Rows.Add(row);
        }
    }

    //show error messages if needed
    Label1.Text = errorMessages;

    return dt;
}

The webforms button click for demo purposes.

protected void Button1_Click(object sender, EventArgs e)
{
    if (FileUpload1.HasFile)
    {
        DataTable dt = ExcelToDataTable(FileUpload1.FileBytes, CheckBox1.Checked);

        GridView1.DataSource = dt;
        GridView1.DataBind();
    }
}