CustomXml Parts are not included in Undo/Redo

[James-Gauld-92]

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When using the undo/redo commands after using an add-in to modify both the worksheet and Custom Xml Parts, only the worksheet changes are Undone/Redone. Leaving potentially stale references to worksheet data in the Custom Xml Parts.

Your Environment

• Platform [PC desktop, Mac, iOS, Office on the web]: PC Desktop
• Host [Excel, Word, PowerPoint, etc.]: Excel
• Office version number: 2511
• Operating System: Windows 11 (25H2)
• Browser (if using Office on the web): ______

Expected behavior

Created Xml Parts should be deleted/recreated with the worksheet changes.

Current behavior

Worksheet changes are undone/redone but the Custom Xml Parts remain in the state created by the initial add-in action.
The [Content_Types].xml file is also left in the previous state.

Steps to reproduce

1. Clone https://github.com/James-Gauld-92/OfficeJs-Excel-Undo-CustomXml-Example
2. Install dependencies and run npm run dev-server
3. Open Excel and sideload the manifest.
4. Click show task pane and then Add Current time to current cell and insert to Custom XML Part.
5. The current time should be inserted to the current cell.
6. Save the Workbook to a local directory.
7. Copy the Workbook in Windows Explorer.
8. Use 7zip to extract the copied Workbook to a folder.
9. Open the extracted files and navigate to customXml.
10. Confirm that the latest item{number}.xml contains the correct date inserted in step 5.
11. Return to Excel and undo the last action.
12. Resave the workbook.
13. Repeat steps 7-9.
14. The customXml item will still be there.
15. If you use the Redo button at this time, the Cell will get the current time back, but there will still only be the original item{number}.xml

Provide additional details

1. workbook.customXmlParts.add Is not listed on the unsupported Api's here https://learn.microsoft.com/en-us/office/dev/add-ins/excel/excel-add-ins-undo-capabilities
2. OneDrive auto save can interfere with this quick test by causing the Workbook file to not synchronise in a timely manner.
3. We have to copy the Workbook as Excel will keep the workbook locked so 7zip cannot access it, also we want to retain the undo history so we can't close Excel.

Context

We use both a hidden sheet and the custom xml parts to track metadata related to the cell contents. Before Api 1.20 the undo history was cleared whenever the Add-in performed any actions, so deleting data in the main sheet could only be done in a way that our Add-in could detect and remove the associated metadata. This was done by detecting #REF! in the hidden sheet, or by having the end user use a dedicated delete button in the Add-in.
Now the main sheet and hidden sheet data can be undone leaving the customXml data behind and leaving the Add-in in a corrupted state.

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[rajatavams]

Hello @James-Gauld-92 , thanks for reporting. We are able to repro the issue and an internal work item (ICM 730948558) has been created to track it further. We’ll share updates on its progress here.

[Nchoursaia]

Hello @James-Gauld-92 , we've looked into this issue and the current behavior of undo for custom parts is by design. To give you a brief - CustomXMLPart add API does not support undo by design, however since it is marked undoable - meaning the API even though does not support undo action, it will not clear the undo stack and retain it, due to which when you undo, the action of adding text into the cell gets undone.
We have reached out to the team to update this particular behavior of APIs in the documentation here.
https://office.visualstudio.com/OC/_wiki/wikis/office-js-api/79091/Excel-API-Undo-Guidance.

[James-Gauld-92]

Hi @Nchoursaia I don't have permission to view that link.
What's the end goal going to be?
Having the CustomXMLParts add API throw the "UndoNotSupported" exception would probably be best if it's not going to get Undo support.
At the moment we are explicitly calling an unsupported action after any attempt to modify the CustomXML in order to clear the Undo stack so that a user can't accidentally get our add-in into an invalid state.

[James-Gauld-92]

Could I get an accesible link or an explaination of what is on that Visual Studio wiki too please?

[Nchoursaia]

I had linked an internal document adding the public documentation link - https://learn.microsoft.com/en-us/office/dev/add-ins/excel/excel-add-ins-undo-capabilities#unsupported-apis.
The API will be retaining the undo stack and not throw an error by design. The undo record for Custom XML Parts is not generated intentionally as there is no UI indication and we don't want to corrupt undo stack in such cases. However, we understand that there may be requirement from certain customers to clear undo stack when the operation doesn't generate undo record. For such scenarios we are discussing exposing an explicit API but we cannot comment on timeline yet. In the meantime, you can use APIs like sheet Unprotect() to clear the undo stack. We have reached out to the internal team to update the documentation with the correct information.