ExcelWorksheet Dimension NullReferenceException

Question

So I have this code for a window:

public partial class List : Window
{
    DataTable table = null;
    ExcelWorksheet ws = null;
    string user = System.Environment.UserName;

    public void Initialize()
    {
        string path = "Log.xlsx";
        FileInfo file = new FileInfo(path);

        try
        {
            if (File.Exists(path))
            {
                using (ExcelPackage pack = new ExcelPackage(file))
                {
                    bool sheetfound = false;

                    //runs through each sheet to find a specific one
                    foreach (ExcelWorksheet sheet in pack.Workbook.Worksheets)
                    {
                        if (sheet.Name.Equals(user))
                        {
                            sheetfound = true;
                            ws = pack.Workbook.Worksheets[user];
                            break;
                        }
                    }

                    //Creates new sheet if it hasn't found the specific one
                    if (!(sheetfound))
                    {
                        ws = MainWindow.Create_Worksheet(pack);
                        pack.Save();
                    }
                }
            }
            else
            {
                using (ExcelPackage pack = new ExcelPackage(file))
                {
                        ExcelWorksheet ws = MainWindow.Create_Worksheet(pack);
                        pack.Save();
                }
            }
        }
        catch (Exception ex)
        {
            MessageBox.Show("Exception caught:\n\n" + ex as string, "Error", MessageBoxButton.OK, MessageBoxImage.Error);
        }

        fUpdate(new Object, new RoutedEventArgs);
    }

    public void fUpdate(object sender, RoutedEventArgs e)
    {
        table.Rows.Clear();

        MessageBox.Show(ws.Dimension.End.Row.ToString());
    }
}

and this one from the main window:

public partial class MainWindow : Window
{
    public static ExcelWorksheet Create_Worksheet(ExcelPackage pack)
    {
        ExcelWorksheet ws = pack.Workbook.Worksheets.Add(System.Environment.UserName);

        ws.Cells[1, 1].Value = "Date";
        ws.Cells[1, 2].Value = "Time";

        ws.View.FreezePanes(2, 1);

        return ws;
    }
}

What this is supposed to do right now is, when the second window launches, it sets the Excel file and worksheet. I used Quickwatch to see if it works and it does work, ws gets set to the specific sheet that I wanted and ws.Dimension.End.Row returns 1. However, after it gets out of the try-catch part (once it reaches fUpdate), ws.Dimension.End.Row suddenly throws a NullReferenceException. I checked and ws is still the same ExcelWorksheet object and it didn't go through anything (that I know of) that would change its value. What causes this error? Thanks!

(ws returns the ExcelWorksheet object but ws.Dimensions return the exception)

Answer 1

The Dimension object of the ExcelWorksheet will be null if the worksheet was just initialized and is empty.

For example:

ExcelWorksheet worksheet = new ExcelPackage().Workbook.Worksheets.Add("Sheet1");
Console.WriteLine(worksheet.Dimension.End.Row);

This code will throw a NullReferenceException since the Dimension object is null.

On the other hand:

ExcelWorksheet worksheet = new ExcelPackage().Workbook.Worksheets.Add("Sheet1");
worksheet.Cells[1, 1].Value = "Some text value";
Console.WriteLine(worksheet.Dimension.End.Row);

This code will not throw an exception since the Dimension object was initialized by adding content to the worksheet.

If the loaded ExcelWorksheet already contains data, you will not face this issue.