Undo operation in DemoConsole causes ContextMenuStrip to become unusable

[Nora-Zhou01]

.NET version

.NET 10.0 main branch of WinForms repo

Did it work in .NET Framework?

Not tested/verified

Did it work in any of the earlier releases of .NET Core or .NET 5+?

Yes, this is a regression issue. Not repro on .NET 9.0 from Release/9.0 branch of WinForms repo.

Issue description

In the DemoConsole test application in the Winforms repo, the Undo operation causes the ContextMenuStrip to be unusable.

.NET 10

democonsole.undo.main.mp4

.NET 9.0

democonsole.undo.9.0.mp4

Steps to reproduce

Test sample: DemoConsole in Winforms repo

1. Click the form designer after Type Text for the ToolstripMenuItem in the ContextMenuStrip
2. Click Undo/Ctrl + Z

[LeafShi1]

This issue caused by PR #11358

[elachlan]

CC: @kirsan31

[kirsan31]

Will look as soon as I can (most likely on the weekend).

[kirsan31]

After brief look:
The problem is that "Type Here" element is not returned to the collection during Undo.
The problem only occur if ContextMenuStrip not selected (not visible) during undo.

There are a lot of additions and deletions going on there (clearly more than necessary). Need more deep investigation...

---------------------UPD---------------------

"Type Here" element Inserted in this method: ToolStripDropDownDesigner.OnSelectionChanged -> ToolStripDropDownDesigner.ShowMenu -> ToolStripDropDownDesigner.ShowMenu -> ToolStripMenuItemDesigner.CreatetypeHereNode only when _initialized flag is not set.
And _initialized flag is set to false in ToolStripDropDownDesigner.DropDownItem_DropDownClosed which is called from ToolStripDropDownDesigner.OnUndone -> ToolStripDropDownDesigner.HideMenu -> ToolStripDropDownDesigner.HideDropDown method only if _dropDown.Visible is true!
And after #4808 fix _dropDown.Visible is false.
Need more time...

---------------------UPD2---------------------

The problem is in ToolStripDropDown.SetVisibleCore:

winforms/src/System.Windows.Forms/src/System/Windows/Forms/Controls/ToolStrips/ToolStripDropDown.cs

Line 1589 in 034543a

CancelEventArgs openEventArgs = new(cancel: DisplayedItems.Count == 0);

After #4808 fix DisplayedItems is empty and therefore we will not show dropdown - _dropDown.Visible is false.
So previously (before #11358) with some conditions we can show empty dropdown (if dropdown is empty but DisplayedItems not). But after fix we can't show non empty dropdown if DisplayedItems is empty.
Need more time...

---------------------UPD3---------------------

The call sequence is:

• remove test element. This lead to empty DisplayedItems after 4808 fix.
• ShowMenu -> CreatetypeHereNode
  • add "Type Here" element
  • ShowDropDown. This will not show dropdown after 4808 fix because of empty DisplayedItems and next steps will not execute.
  • SetDisplayedItems
• HideDropDown
• ...

So theoretically we can change the order of SetDisplayedItems and ShowDropDown and all will work.
But it's becoming more and more complicated. And I advice to revert 4808 fix.

[Tanya-Solyanik]

@Nora-Zhou01 - do you see any similar problems in the Visual Studio designer for applications targeting NET9?

[kirsan31]

@Nora-Zhou01 - do you see any similar problems in the Visual Studio designer for applications targeting NET9?

Them shouldn't be there, the problem is in the fix described above (main branch). And I suggested to roll it back.

[John-Qiao]

Verified this issue on winforms repo from main branch, it has been fixed: the ContextMenuStrip works well after clicked Undo.

testresult.mp4