Compiler Warning WFDEV004

Version introduced: .NET 10 Preview 1

Form.OnClosing, Form.OnClosed and the corresponding events are obsolete. Use Form.OnFormClosing, Form.OnFormClosed, Form.FormClosing and Form.FormClosed instead.

These methods and events are provided for backwards compatibility and they shouldn't be used. Instead, reference the replacement methods and events.

Workaround

Replace the obsolete member with the new member:

Old member	New member
Form.OnClosing	Form.OnFormClosing
Form.OnClosed	Form.OnFormClosed
Form.Closing	Form.FormClosing
Form.Closed	Form.FormClosed

Suppress a warning

Suppress the warning with either of the following methods:

• Set the severity of the rule in the .editorConfig file.

  [*.{cs,vb}]
  dotnet_diagnostic.WFDEV004.severity = none
  

  For more information about editor config files, see Configuration files for code analysis rules.

• Add the following PropertyGroup to your project file:

  <PropertyGroup>
      <NoWarn>$(NoWarn);WFDEV004</NoWarn>
  </PropertyGroup>
  

• Suppress in code with the #pragma warning disable WFDEV004 directive.

For more information, see How to suppress code analysis warnings.