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You cannot switch off an AI coding agent’s tendency to fill gaps with plausible guesses, but you can make those guesses much easier to catch before they reach your app. Give the agent a bounded task, name the files and symbols it should work from, list what must stay the same, and then review the diff, build the project, and inspect SwiftUI previews on the platforms and states that matter. Apple’s documented Xcode coding-intelligence and preview tools support this loop. They make errors easier to find; they do not guarantee that the agent will stop inventing UI.
Informal developer posts describe generated code as “almost SwiftUI” and say agents can be “confidently wrong” about Apple’s Human Interface Guidelines. Treat that wording as anecdote. It shows a common frustration, not how often the problem occurs.
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Why agents invent UI when you ask for a change
A vague request leaves decisions open: where a button sits, which navigation pattern applies, what spacing a list uses, whether a toolbar already exists. An agent that lacks the surrounding code will supply its own answer to each open decision. The result often compiles and looks reasonable in isolation, but it no longer matches the screen it was supposed to modify.
Xcode’s documentation says the tool gathers relevant context automatically, based on your prompt and the conversation history. Automatic gathering is not the same as knowing your design. The steps below close that gap deliberately.
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Set the boundaries before the agent writes anything
Describe the change as a visible outcome
Write the request in terms of the exact view or behavior, the platform and deployment context, and what a person should see afterward. “Add a remove action to each row in the order detail list, shown as a trailing swipe action on iPhone and as a context menu on iPad” gives the agent a target. “Make the orders screen better” does not.
List what must stay the same
Preservation constraints are the most effective single addition to a prompt. Name what the agent must not touch and ask it to change nothing else unless the request requires it. Useful items include:
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- The existing navigation structure, including stack versus split-view layout
- Spacing, padding, and font choices already used on the screen
- Controls that exist today and their current actions
- Shared components that other screens depend on
- Data models and view-model signatures, unless the change explicitly alters them
Also ask the agent to list any assumptions or project details it does not have before it invents replacements. A question such as “Which file defines the shared row component?” is cheaper to answer than a rewritten screen.
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Give the agent the project context it is missing
Apple’s Xcode coding-intelligence documentation describes referring to symbols and files with @, adding explicit context to prompts, and uploading files. Use these features to point at the material that determines how the new UI should fit:
- The current view that the change modifies
- Any shared components, styles, or design tokens the view uses
- The navigation code that presents the view, such as the parent stack or sheet
- One existing screen that already follows the pattern you want to reuse
The exact choice of context is practical judgment rather than a checklist Apple publishes. The principle is simple: the more of the real code the agent reads, the fewer decisions it has to improvise.
Review every changed file before accepting it
- Open the comparison for each edited file. Xcode’s coding tools present changes so you can compare them against the previous version. Check every file, not just the one you expected to change.
- Ask for a rationale for each UI element or modifier. A new
.padding(),.toolbaritem, or wrapper view should have a reason tied to your request. If the explanation is “for consistency” with nothing named, treat it as suspect. - Reject unrelated edits. Reformatting, renamed properties, and restyled neighboring views are common side effects. Reject them rather than letting them ride along with the feature change.
- Use undo or rollback when a direction is wrong. Xcode preserves conversations and offers undo or rollback to an earlier state, so a bad pass does not need to be repaired by hand.
Build, then preview: two different checks
Building and previewing answer different questions, and both are necessary. Apple says an Xcode agent can iterate, build to verify code, and fix warnings and errors. A successful build confirms that the code compiles under your current project configuration.
Previews show the rendered result. Apple describes SwiftUI previews as dynamic, interactive previews of custom views, and its coding-tools documentation says previews can be used to validate UI code across platforms. Playgrounds and previews also let you try code without modifying the app. Apple’s source-editor documentation puts it this way: “Playgrounds and previews let you experiment with new code without modifying your app.”
| Check | What it establishes | What it does not establish |
|---|---|---|
| Diff review | Every changed line is one you can explain and accept | Whether the explanation is correct for your design |
| Build | The code compiles in the current project configuration, with warnings and errors surfaced | Whether the layout, navigation, or visual hierarchy is right |
| Preview | How the custom view renders for the previewed device sizes, platform variants, and data states | Every interaction, accessibility need, or product requirement; behavior on states you did not preview |
| Human design review | Whether the result matches the task and your product’s design standards | Nothing automated; this step is the judgment the other three cannot replace |
For the preview step, check at least the following before you call a change finished:
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- The smallest and largest device sizes the screen supports
- Each platform variant the feature ships on, such as iPhone and iPad
- Empty data, a typical populated list, and an unusually long string
- The interaction states the change touches, such as selected, disabled, or presented as a sheet
When the preview is wrong, iterate from a specific discrepancy
Vague feedback such as “this looks off” invites another round of invention. Narrow the correction instead:
- Name the element, the expected placement or behavior, and the constraint it broke. For example: “The delete action is a trailing swipe on iPhone but appears in the toolbar on iPad; the constraint is that the toolbar must keep only its existing items.”
- Ask for the smallest change that fixes that one discrepancy.
- Review the new diff, build again, and re-check the same preview states.
Repeat this loop one discrepancy at a time. If several problems appear at once, fix them in separate passes so you can tell which change caused which result.
What this workflow does and does not promise
The goal is to reduce the chance that unwanted output survives review. Prompting with constraints, supplying context, and checking diffs, builds, and previews make invented APIs and unsolicited UI easier to spot. Apple’s documentation describes these tools and review loops; it does not present them as a way to eliminate fabricated APIs or design errors. Keep your own review in the loop for every change that reaches users.
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