SHDocVw.InternetExplorer DocumentComplete blocked since Win10 update 1809

[toniarnold]

In theory, SHDocVw.InternetExplorer once required the Single-Threaded Aparment (STA), but this was no longer the case in the given context on Win10. Probably since Win10 update 1809 (retarded April 2019 version), even enforcing Apartment(ApartmentState.STA) (missing in .NET core) on the TestFixture causes the DocumentComplete event to time out after the second request – surprisingly, there is no difference whether the TestFixture nominally runs in the STA or the MTA.

Only workaround known today (tedious): A Visual Studio breakpoint at the end of IEExtensionBase.SetUpIE(), thus after each IE startup, precariously restores the old behavior and usually causes the tests to pass.

[toniarnold]

The empirical suspicion that vanishing COM/MTA/STA problems had something to do with the attached debugger was wrong: SHDocVw.InternetExplorer lately more aggressively grabs focus, and this now heavily interferes with programmatic control – the visual appearance of IE is ahead of its state visible to COM. Before update 1809, such problems sometimes arose when not refraining from touching the mouse, now they’re persistent, a true blocker.

New workaround: IE’s visible property now defaults to false, just like it originally was required on Win7. This can be overridden with SetUpIE(visible: true) in the test fixture for manual troubleshooting, but this requires to manually and immediately push IE into the background after starting up. Automatically opening a second IE over the testing one turned out to be unreliable, as the testing instance repetitively grabbed focus over the empty one again.