Introduction

In iOS, sending SMS from Swift is handled through MessageUI and MFMessageComposeViewController. Apps cannot send texts silently without user interaction. The supported flow presents the native composer, pre-fills recipient and body, and lets the user confirm send or cancel.

Many short answers solve the immediate syntax problem but skip operational concerns such as reliability, observability, and long-term maintenance. A stronger implementation combines correct API usage with explicit edge-case handling, predictable failure behavior, and test coverage that protects against regressions.

Before shipping, clarify assumptions around input shape, nullability, concurrency model, and runtime environment. Writing those assumptions down in code comments or tests prevents future contributors from accidentally changing behavior while doing seemingly harmless refactors.

Core Sections

1. Start with the smallest correct implementation

Use canSendText() before presenting the composer and conform to MFMessageComposeViewControllerDelegate for completion handling. This avoids runtime issues on unsupported devices.

1import MessageUI
2
3final class SmsViewController: UIViewController, MFMessageComposeViewControllerDelegate {
4    func sendSMS() {
5        guard MFMessageComposeViewController.canSendText() else {
6            print('SMS not available')
7            return
8        }
9
10        let vc = MFMessageComposeViewController()
11        vc.body = "Your verification code is 123456"
12        vc.recipients = ["+15551234567"]
13        vc.messageComposeDelegate = self
14        present(vc, animated: true)
15    }
16
17    func messageComposeViewController(_ controller: MFMessageComposeViewController,
18                                      didFinishWith result: MessageComposeResult) {
19        controller.dismiss(animated: true)
20    }
21}

A minimal baseline is useful because it creates a known-good reference. Keep the first version easy to read, then verify expected behavior with one happy-path and one boundary test before adding optimization or abstraction.

2. Harden the implementation for production behavior

If you only need to open the Messages app without in-app compose controls, use the sms: URL scheme. This is less integrated but can be sufficient for simple contact actions.

1if let url = URL(string: "sms:+15551234567"), UIApplication.shared.canOpenURL(url) {
2    UIApplication.shared.open(url)
3}
4
5// Keep user privacy expectations clear in UI copy.

Hardening usually means explicit error handling, input validation, and lifecycle management of resources such as files, database sessions, network calls, and UI state. It also means making contracts clear so callers know what failures to expect and how to recover.

3. Validate results and monitor over time

Design UX around user consent and platform constraints. Explain why messaging is needed and what data will be prefilled. Also test on real devices, because simulator behavior is limited for telephony features. Keep analytics around send flow outcomes to detect friction and optimize completion rates.

For durable quality, add a compact verification loop: unit tests for core logic, one integration test for boundary interactions, and basic instrumentation for latency or failure rates in real environments. If metrics drift after changes, use that signal to investigate before user impact grows.

A practical rollout checklist improves long-term reliability. Define expected input and output examples, then codify them in tests that run in CI. Add one negative test for malformed input and one resilience test for temporary dependency failure. Even lightweight checks dramatically reduce regressions when teammates refactor surrounding code or upgrade frameworks.

Operational visibility matters just as much as correct code. Emit structured logs for key decision points, include identifiers needed for tracing, and track one or two metrics that reflect user impact. When incidents happen, these signals shorten time-to-diagnosis and prevent repeated guesswork across releases.

Finally, document versioning and rollback expectations near the implementation. A small runbook entry that states how to verify success, how to detect failure quickly, and how to revert safely can save significant time during outages. Teams that capture this context early usually ship faster because incident response becomes routine rather than improvisational.

Common Pitfalls

• Trying to send SMS silently without presenting system UI.
• Skipping canSendText() checks and failing on unsupported devices.
• Forgetting delegate assignment and leaving compose screen stuck.
• Testing only on simulator and missing real-device behavior differences.
• Embedding sensitive data in prefilled SMS body without policy review.

Summary

Use MFMessageComposeViewController for supported in-app SMS composition and rely on user confirmation. Respect platform limitations, handle fallbacks, and test on real devices. Pair concise implementation with explicit tests and runtime checks to keep the solution dependable as requirements evolve.