First App.
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CHAPTER 04Lesson 14 of 36

Make one action work

Make one button do one useful thing.

In Codex6 min read & do
By the end of this lesson

Complete a small action in the app and check the result.

Let’s do this

  1. 1
    In Codex

    Choose the main action

    Use your first-version checklist. Say exactly what happens before the action, what the person enters or taps, and what should happen afterwards.

  2. 2
    In Codex

    Ask for a small change

    For an Add action, describe the fields, Save button and Cancel button. Ask Codex to prevent empty entries and keep the screen understandable. Avoid adding a second unrelated feature in the same request.

  3. 3
    In Xcode

    Run the updated app

    In Xcode, press Run again. Try a normal entry. Then cancel an entry and try submitting an empty one. A button that looks right but does nothing is not finished.

  4. 4
    In Codex

    Describe the result

    Tell Codex what you expected and what happened. If a record disappears after closing the app, note that separately; the saving lesson makes records last between launches.

Xcode project window with Swift code and an iPhone preview showing a globe and Hello, world.View larger
Apple’s current guide uses this example. Your app’s name and version will differ.Screenshot source (opens a new tab)

A message for Codex

In my first iPhone app, implement the first useful action from our plan for [describe the problem my app should solve]. Use the smallest complete interaction. Include a clear way to save and cancel, and a helpful response to empty or invalid input. Do not add unrelated features. Build-check it and give me three taps or actions I can use to verify it in the simulator.

Make this message fit your idea.

What you should see

You can complete the main action, cancel it safely and understand what happens when information is missing.

If you get stuck

Go at your own pace. There is no test to pass.

Checked 7 September 2026. Screens can change; the official guides below have the latest steps.

Run on a simulator or deviceApple’s design guidance