[Technical Questions] Sending ‘self’ risks causing data races in MFMailComposeViewControllerDelegate

[jennleww]

In what area do you have a technical challenge?

Xcode, Simulator & Previews

Description

I am encountering a warning in my Swift code when implementing MFMailComposeViewControllerDelegate within a UIViewControllerRepresentable wrapper for SwiftUI. The warning states:
“Sending ‘self’ risks causing data races”

This occurs within my Coordinator class in the mailComposeController function when attempting to call:

self.parent.completion?(result)

I am unsure of the correct way to resolve this issue without introducing memory management problems or breaking functionality.

Reproduction

• Create a UIViewControllerRepresentable struct (MailView) that wraps MFMailComposeViewController.
• Implement a Coordinator class conforming to MFMailComposeViewControllerDelegate.
• In the mailComposeController function, call self.parent.completion?(result).
• Observe that Xcode shows the warning “Sending ‘self’ risks causing data races”.

Expected behavior

I expect the completion closure to execute without data race issues and for the mail composer to dismiss properly upon completion. Ideally, I would like a solution that ensures thread safety while maintaining functionality.

Additional context

No response

Code of Conduct

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[vishnuravi]

Hi @jennleww, you should be able to fix this problem by calling your completion handler from the main thread with a weak capture of self, like this

    func mailComposeController(_ controller: MFMailComposeViewController,
                               didFinishWith result: MFMailComposeResult,
                               error: Error?) {
        // Explicitly dispatch UI updates to the main thread
        DispatchQueue.main.async { [weak self] in
            guard let self else { return }
            self.parent.completion?(result)
            controller.dismiss(animated: true)
        }
    }