First App.
Your learning space A little progress, every day
CHAPTER 04Lesson 12 of 36

Build the first screen

Turn a small part of your idea into something you can see.

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

Have a first screen that matches the agreed plan.

Let’s do this

  1. 1
    In Codex

    Ask for the first screen only

    Use the plan you approved. Tell Codex the title, main content and main button you want. Ask it to use normal iPhone controls so text sizes, spacing and navigation behave in familiar ways.

  2. 2
    In Codex

    Let Codex work in the project

    Codex will edit files. Read any access request and approve only what fits this work. You do not need to paste its code into Xcode manually if it is already changing the correct project folder.

  3. 3
    In Codex

    Read its handover

    Ask which files changed and whether it checked that the project builds. A message saying “done” does not prove the screen works. Ask for the build result and the step you should take next.

  4. 4
    In Codex

    Open the project in Xcode

    Bring Xcode to the front. It usually notices saved file changes. If the preview on the right is paused, resume it if available. The next lesson uses the full simulator, so a paused preview is not a reason to start another project.

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

Implement only the first screen of my first iPhone app using the plan we agreed. Its purpose is [describe the problem my app should solve]. Use native SwiftUI controls, readable text and one clear main action. Keep any sample records clearly labelled as examples. Work in the existing project. Build-check your changes and tell me the result, the files changed and exactly how to see the screen in Xcode. Do not add extra features yet.

Make this message fit your idea.

What you should see

The project contains the new screen and Codex has reported whether the build check passed. You are ready to run it in the simulator.

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.

Create an iPhone projectRun on a simulator or device