An exception popped up when click "Type Here" on ContextMenuStrip control in DemoConsole application

[MelonWang1]

.NET version

.NET 8.0.100-preview.7.23330.16

Did it work in .NET Framework?

Yes

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

It also repro's in .NET 7.0.

Issue description

In Winforms repo, there has a DemoConsole test app, System.NullReferenceException: 'Object reference not set to an instance of an object.' occurs when click "Type Here" on ContextMenuStrip control in DemoConsole application.

https://github.com/dotnet/winforms/assets/94418985/4ae6cb77-9592-41ae-96df-65fe24d9241b

Call Stack: System.NullReferenceException HResult=0x80004003 Message=Object reference not set to an instance of an object. Source=System.Windows.Forms.Design StackTrace: at System.Windows.Forms.Design.ToolStripMenuItemDesigner.InitializeDropDown() in C:\test\winforms\src\System.Windows.Forms.Design\src\System\Windows\Forms\Design\ToolStripMenuItemDesigner.cs:line 1618

Steps to reproduce

Test sample: DemoConsole in Winforms repo

[elachlan]

MenuItem.Owner is null for some reason.

[elachlan]

@MelonWang1 does it repro in .net6?

[MelonWang1]

@elachlan NET 6.0 fails when I build it in Winforms repo.

[elachlan]

EditTemplateNode in ToolStripMenuItemDesigner calls InitializeDropDown for the designer for a "dummyItem" created via CreateDummyItem. For whatever reason the dummy item has no owner, hence the exception. The owner is set when the item is added to a ToolStripItemCollection. But I don't think this is ever done for the dummy item.

If we wrap the Invalidate call in a null check:

if (MenuItem.Owner is not null)
{
    GetService<BehaviorService>()?.Invalidate(MenuItem.Owner.Bounds);
}

This ends up triggering an assert at: https://github.com/dotnet/winforms/blob/386d51b6a85689a0964d0596e8e0d03a471fc225/src/System.Windows.Forms.Design/src/System/Windows/Forms/Design/ToolStripItemDesigner.cs#L1219

Hope that helps.

[elachlan]

@dmitrii-drobotov any suggestions here I am a bit stuck.

[dmitrii-drobotov]

It also reproduced in release/6.0 branch. I will take a look.

[dkazennov]

@elachlan I'll take a look a little bit closer. Need some more time to investigate. Probably will come with some solution next week.

[dkazennov]

So this Issue only reproduces in DemoConsole. It has not been reported in Windows Forms applications and it doesn't reproduce there. We must take a cation: any change in ToolStripMenuItemDesigner may lead for unforeseen regression.

And we can't simply assign newItem.Owner in CreateDummyItem(). This leads to exceptions in ToolStripItemDesigner.CommitEdit()

[dkazennov]

@dmitrii-drobotov any suggestions here I am a bit stuck.

I suppose it should have low priority since there were no reports of the similar problem in production. We can remove ContextMenuStrip from the DemoConsole or refactor it's MainForm to see if it can be added some other way (without surface.CreateControl maybe?).

But this Issue can show some very rare problem.

[Syareel-Sukeri]

Verified this on latest winforms repo from main branch, this issue was fixed. No exception popped up when click "Type Here" on ContextMenuStrip control in DemoConsole application.

https://github.com/dotnet/winforms/assets/156630333/8768d138-8f79-42b8-a884-6a09a35e11d8

[Syareel-Sukeri]

Verified this on latest release/9.0-preview3 branch from winforms repo, this issue was fixed. Test result is the same as above.