Changes to nullability annotations (Windows Forms)
In .NET 9, some nullability annotations on the Windows Forms APIs have changed.
Previous behavior
Previously, some parameters were marked as nullable.
New behavior
Starting in .NET 9, these parameters are marked as non-nullable. If you pass an argument that might be null, you'll get a compiler warning.
Version introduced
.NET 9 Preview 1
Type of breaking change
This change can affect source compatibility.
Reason for change
The parameter on IWindowsFormsEditorService.DropDownControl(Control) was previously marked as nullable, but there's no guidance for implementers on how they should handle null input. Also, logically this method should not accept null.
Affected APIs
The following table lists the affected APIs:
| API | What changed | Recommended action |
|---|---|---|
| IWindowsFormsEditorService.DropDownControl(Control) | The control parameter is non-nullable |
Make sure you're not passing a nullable Control to this method. Also, update any implementations of IWindowsFormsEditorService to remove nullability of the DropDownControl method's parameter. |
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