The WinformsControlTest project exited when clicking Column2 header after clicked the Change DGV font button

[Zheng-Li01]

.NET version

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+?

Repro in release/10.0, release/9.0, release/8.0 branch

Issue description

The WinformsControlTest project exited when clicking Column2 header after clicked the Change DGV font button

CallStack.mp4

Steps to reproduce

Test the sample app: WinformsControlTest in Winforms repo

1. Run the WinformsControlTest project
2. Click the DataGridView button to open the DataGridView dialog
3. Click the Change DGV font button
4. Click the Column2 header

Call Stack:

System.ArgumentException
  HResult=0x80070057
  Message=Object must be of type String.
  Source=System.Private.CoreLib
  StackTrace:
   at System.String.CompareTo(Object value)
   at System.Collections.Comparer.Compare(Object a, Object b)
   at System.Windows.Forms.DataGridViewRowCollection.RowComparer.CompareObjects(Object value1, Object value2, Int32 rowIndex1, Int32 rowIndex2) in C:\Users\v-olzhan\source\repos\winforms\src\System.Windows.Forms\System\Windows\Forms\Controls\DataGridView\DataGridViewRowCollection.RowComparer.cs:line 114

[Olina-Zhang]

Summary

The issue occurs when a DataGridView column contains mixed value types (e.g., string and Font). Although DataGridViewCell.Value accepts object, the built-in sorting logic assumes consistent types within a column.

When the user triggers sorting (e.g., by clicking the column header), the control internally calls String.CompareTo(object). If one of the values is not a string, this results in an ArgumentException:

Object must be of type String.

This exception is not handled by the control and causes the application to terminate.

Key Point

While mixing value types is technically allowed by the API, DataGridView does not handle this scenario gracefully during sorting, leading to a runtime crash instead of a safe fallback or clearer error handling.

[Zheng-Li01]

Verified the issue with the latest main branch of Winforms repo, the issue has been fixed that the WinFormsControlTest project running well as below screenshot.

VerifiedIssue.mp4

[Zheng-Li01]

Verified the issue with the release/11.0-Preview4 branch of Winforms repo, the issue has been fixed that have the same results as above.