WebView2 WinForms control in Excel VSTO Task pane steals and holds on to keyboard focus

[ShaunLoganOracle]

Description
I have a Winforms WebView2 hosted in an Excel VSTO Task pane, There is no System.Windows.Forms.Form hosting the WebView2 control, instead, a System.Windows.Forms.UserControl is the owner/host of the control. After giving the WebView2 focus, it holds on to it after I've clicked back into the Excel worksheet.

Version
SDK: 1.0.705.50
Runtime: Evergreen RT 88.0.705.68
Framework: WinForms
OS: Win10 1909

Repro Steps

1. Render some fairly simple static HTML in the WebView2
2. Click in a worksheet cell, verify that keystrokes are acted on there (eg. right-arrow moves selected cell)
3. Click in the HTML content in the WebView2 (in the task pane), verify that keystrokes are acted on there (eg. Enter toggles an expand/collapse widget)
4. Click back in a different worksheet cell
   Observed: selected cell is changed as expected, however keystrokes are still getting captured by WebView2 (ie. Enter toggles the HTML widget instead of moving the cell selection).

AB#36775741

[champnic]

Thanks for finding this issue @ShaunLoganOracle - we have some other bugs around VSTO Task Panes and I think they probably share a common root cause. I've created a bug on our backlog and we'll take a look.

[alaincao]

I have that same behaviour with a project using Custom Task Panes from ExcelDNA.

• SDK: "1.0.865-prerelease"
• Runtime: 90.0.818.51

FYI, a demo project to reproduce can be found there: https://github.com/alaincao/ExcelDNASamples/tree/webview2_issue_933/CustomTaskPane

[ShaunLoganOracle]

@champnic
Update: I still see issues with keyboard focus getting stuck using SDK 1.0.902.49 and WV2 runtime 93.0.961.38
The bad behavior in #933 where there was a crash/hang is fixed. However the behavior of keyboard focus getting stuck in the WebView2-rendered content is still there. To add to that, the F6 and Shift-F6 keys seem to be ignored/swallowed by WV2. In Excel, these keys should move the focus from the VSTO task pane to other controls in Excel (the ribbon, worksheet grid, etc.). Since these are ignored, this makes the WebView2 control in the task pane a "keyboard trap" - thus it is an accessibility issue.

[ShaunLoganOracle]

@champnic
Update: customers are still encountering this "focus getting stuck" issue using WV2 RT 98.0.1108.55 and our add-in code using the WV2 SDK 1.0.902.49. As our adoption of WebView2 gets wider distribution among our customers, the frequency (and annoyance) of this issue increases.
We would be glad to explore a code-around if there is something our code could do to avoid this issue.

[champnic]

Hey @ShaunLoganOracle - Can you try this potential workaround?

Before initializing your WebView2, call:
SetEnvironmentVariable(L"COREWEBVIEW2_FORCED_HOSTING_MODE", L"COREWEBVIEW2_HOSTING_MODE_WINDOW_TO_VISUAL");

If that resolves the issue, then we are currently working on a better solution which should fix this automatically. That workaround also won't work on Win 7/8/8.1.

[ShaunLoganOracle]

Thanks. My add-in supports Win 10 & 11 only so I'll try this shortly and report back.

[ShaunLoganOracle]

I tried this by setting a System Environment variable (as spec'd above) in the Settings app and then running Excel and trying my use case. The stolen keyboard focus issue seems be resolved!
I did see something a little unexpected - now when I mouse click into the WebView2 hosted in the VSTO task pane - it does not appear to get keyboard focus at all (focus stays where it was, in my case: the worksheet grid). If I use F6 to activate the task pane, then the content in the WV2 control does get focus.
I will need to run additional tests to confirm no ill effects across my use cases, but this looks promising as a workaround that customers can even use without an updated add-in. Thanks!
I look forward to the "better solution which should fix this automatically".

[ShaunLoganOracle]

Observation: by setting this environment variable programmatically in my add-in (running in the Excel process), any other usages of WebView2 in that process will presumably have their behavior changed too. For example if there was another add-in using WebView2, it would be affected.

[ShaunLoganOracle]

@champnic
After some more testing, I have to report that this workaround setting the env. variable does not work for us. Yes, it appears to resolve the issue in the VSTO Task Pane, but it causes another worse issue. In addition to using WV2 in the Task Pane, we also have some modal WinForms dialog that host WV2 controls that render, for example, login pages. With the environment variable set, it seems that the html content never gets keyboard focus. So for example, tabbing from the username input box to the password input box does not work - the Tab key is ignored. This is a blocker for us. Without the env. variable set, the Tab key works as expected in these login pages in WV2.
Edit: some keys are seen by the control (Backspace, Esc), but others (Tab, left/right/up/down arrows) are not.

[champnic]

@ShaunLoganOracle Thanks for trying it out. The fact that it fixes the original issue does suggest that the other work we are doing will fix this when it's completed. It's unfortunate the side effects mean you can't use the workaround yet though, sorry about that.