An attempt to load a workbook from a file causes the WPF program to freeze

[MOP3E]

Bug description
The project is based on WPF, .NET Framework 4.8, NanoXLSX 3.0.0. An attempt to load a workbook from a file using WorkbookReader.Load causes the program to freeze.

There is no freeze in the console application.

Steps To Reproduce
Steps to reproduce the behavior:

1. Create a WPF Project.
2. Install nuget NanoXLSX 3.0.0.
3. Add Button into MainWindow.XAML and create the handler of Click event:
   private void Button_Click(object sender, RoutedEventArgs e)
   {
   Workbook workbook = WorkbookReader.Load("d:\\tags.xlsx"); *
   MessageBox.Show(workbook.Filename);
   }
4. Compile project, press button and program freeze.

* Instead of "d:\\tags.xlsx" substitute the name of any existing Excel file.

[rabanti-github]

Hi,
Just for clarification (I am not on a PC right now):
With "freeze", do you mean, that the UI is not responsive for a time (e.g. 2-3 seconds), or is the app completely freezing and you have to stop it manually?
If the app is becoming responsive again, then you could try LoadAsync instead of Load. This is anyway advised for UI-related projects.
Unfortunately, there is not yet a demo for that (only for save). But basically you have to use await.
Can you try this out?

[MOP3E]

Hi, The user interface completely stops responding. Sincerely, software engineer Alexey Nikolaevich Ovodkov. From: Raphael Stoeckli ***@***.***> Sent: Friday, April 24, 2026 3:41 PM To: rabanti-github/NanoXLSX ***@***.***> Cc: MOP3E ***@***.***>; Author ***@***.***> Subject: Re: [rabanti-github/NanoXLSX] An attempt to load a workbook from a file causes the WPF program to freeze (Issue #84) <https://avatars.githubusercontent.com/u/6697127?s=20&v=4> rabanti-github left a comment (rabanti-github/NanoXLSX#84) <#84 (comment)> Hi, Just for clarification (I am not on a PC right now): With "freeze", do you mean, that the UI is not responsive for a time (e.g. 2-3 seconds), or is the app completely freezing and you have to stop it manually? If the app is becoming responsive again, then you could try LoadAsync instead of Load. This is anyway advised for UI-related projects. Unfortunately, there is not yet a demo for that (only for save). But basically you have to use await. Can you try this out? — Reply to this email directly, view it on GitHub <#84 (comment)> , or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAOY7VJPQQHPZWPK4NGL4QD4XNOGHAVCNFSM6AAAAACYEZICDCVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHM2DGMJTGIYTKNZZGY> . You are receiving this because you authored the thread. <https://github.com/notifications/beacon/AAOY7VMXHFGSWDRNOVVIDZL4XNOGHBFCNFSM6AAAAACYEZICDCWGG33NNVSW45C7OR4XAZNMJFZXG5LFINXW23LFNZ2KUY3PNVWWK3TUL5UWJTYAAAAACAIWOM2KM4TFMFZW63VGMF2XI2DPOI.gif> Message ID: ***@***.*** ***@***.***> >

[rabanti-github]

That's an interesting one.
We had right the same issue about two years back solved, at least for WinForms, as it looks now.
The problem is well known: Await, and UI, and deadlocks! Oh my!, and the solution from two years ago seems only partially working...
However, the quick fix - and also always recommended in the UI realm - is async. This will work always:

        private async void Button_Click(object sender, RoutedEventArgs e)
        {
            Workbook workbook = await WorkbookReader.LoadAsync(@"d:\\tags.xlsx");
            MessageBox.Show(workbook.Filename); // This returns null at the moment. Not sure whether this is a bug or initially intended
        }

Nevertheless, there is still a bug, if a user prefers not using async. I will have a look, how we can solve this.
It is not clear whether it is feasible without an explicit ReaderOption, since I would like to prevent thread analysis at runtime.
But I will certainly work on this.
The Filename issue might also worth being looked at.

[rabanti-github]

Update: It looks like the introduced solution is broken, since v3.0.0 in .Net4.x all .NET versions (regression). Currently, the non-async Load function seems not to wok for WPF and WinForms. Working on it.

[rabanti-github]

The issue should be fixed with the new version of NanoXLSX v3.0.1 (meta-package and NanoXLSX.Reader).
Both packages are already available in NuGet:

• Fixed async handling (regression bug)
• Fixed a bug of the worksheet order, when worksheets were swapped manually in Excel
• Added filename to the workbook object, when loaded from a file (was null)

Please let me know, if something is not working as expected