Center dialogs and message boxes on their parent window

[Tomas Hansson (tomashan)]

Summary

Dialogs and message boxes were shown without an explicit owner, so FormStartPosition.CenterParent had no parent to center against and placement fell back to inconsistent, sometimes off-monitor behavior (especially for non-modal Form.Show(), which never infers an owner).

This change passes the parent form explicitly to ShowDialog/Show/MessageBox.Show throughout MainForm, RDPConnect, AssetLibrarySearch, AddNSG, Parameters, and ChooseProject, so every dialog centers on and stays stacked above its parent, on the parent's monitor.

Test plan

• Built the solution locally (msbuild 2LCS.sln) — succeeds with no warnings/errors
• Verified each touched form still compiles and dialog/messagebox calls pass the correct owner

[Tomas Hansson (tomashan)]

@microsoft-github-policy-service agree

[Florian Hopfner (FH-Inway)]

Tomas Hansson (@tomashan) Thanks for reporting and the pr. I will take a closer look after I'm back from vacation.
In the mean time, could you share screenshots that show the issue so it is easier to repro and validate the solution? From the description, it sounds like a multi-monitor setup issue?

[Tomas Hansson (tomashan)]

Florian Hopfner (@FH-Inway) Thanks, no rush - enjoy the rest of your vacation!

Good question, but it's not multi-monitor specific - I can reproduce it on a single monitor too. A screenshot doesn't really capture the bug well, since the issue is that the dialog's position has no relationship to the parent's position at all. Here's a diagram instead:

Left panel (before the fix): the same main window is shown in two positions (1 and 2). In both cases ShowDialog() / MessageBox.Show() were called with no owner, so FormStartPosition.CenterParent has nothing to center against, and WinForms falls back to a fixed default position - the dialog lands in the same spot every time, regardless of where the parent window actually is.

Right panel (after the fix): with ShowDialog(this) / MessageBox.Show(this, ...), CenterParent has an owner to measure against, so the dialog re-centers on wherever the parent currently sits.

Happy to put together real screenshots too once you're back if that's still useful, but I think this shows the root cause more clearly than a screen capture would.

[Florian Hopfner (FH-Inway)]

Thanks for the diagram, that was helpful.

I tried various ways to reproduce the issue, but was not quite successful. It seems that the issue may only occur with dialogs that are generated during runtime, but have no explicit form defined?

Best result was when I tried the "RDP and passwords > Show passwords" dialog from a cloud hosted instance context menu (right click). There before the pr changes, when having the main window on a monitor different from the main monitor, the dialog is shown near the top left corner of the main monitor. With the pr changes, it shows the dialog on the same monitor as the main form, but still near the top left corner, not centered on the main form.

In any case, the pr changes are looking good, so I went ahead and merged them. This is now available in version 0.54.0. Thanks for the fixes.

In case you want to follow up, I also noticed that the AssetLibrarySearch form does not have the StartPosition property set to CenterParent, causing it to always be displayed on the main monitor near the top left corner.