Implementing Autocomplete Search in Mobile Apps

We provide end-to-end development of autocomplete search in mobile apps: query architecture, debounce, cancellation of stale requests, caching of suggestions, search history, and highlight of matches. The task is solved on Swift, Kotlin, Dart, and React Native. From our practice: in one project switching to autocomplete reduced time to first result from 2.1 seconds to 0.4 seconds — search conversion increased by 18%.

Two main pain points are race conditions and keyboard overlap. Race condition: a response to an outdated request arrives later than a new one and overwrites the suggestion list. The solution — flatMapLatest (Android) or switchToLatest() (iOS): upon a new character, the previous request is automatically cancelled. The keyboard overlaps suggestions if the list's bottom anchor is attached to the screen rather than to the keyboard. We fix this via KeyboardAvoiding (RN) or WindowInsetsCompat (Android), discussing this detail with the designer before writing code.

Developing such search covers several technical stages: architecture selection, debounce, cache, history, and highlighting. Below is the specific mechanics of each with code examples.

Choosing the Approach: Client-Side or Server-Side Search?

The choice of search architecture determines development time and offline behavior. Three working options:

Client-side search via fuse.js is faster than server-side for small datasets and requires no network. The combined approach is more effective for eCommerce: instant response from local cache, background API refresh.

Debounce and Cancellation of Stale Requests

Without debounce, the search sends a request for every typed character. At a typing speed of 3–5 characters per second — that's 3–5 extra network calls. Responses arrive out of order, the suggestion list flickers. A 300 ms debounce eliminates the problem: the request is sent only after a pause in typing.

// iOS: debounce via Combine
@Published var query = ""
cancellable = $query
    .debounce(for: .milliseconds(300), scheduler: RunLoop.main)
    .removeDuplicates()
    .flatMap { [weak self] q in
        self?.fetchSuggestions(q) ?? Empty().eraseToAnyPublisher()
    }
    .sink { [weak self] in self?.suggestions = $0 }

// Android: debounce via Flow + coroutines
searchFlow
    .debounce(300)
    .distinctUntilChanged()
    .flatMapLatest { query -> suggestionsUseCase(query) }
    .collect { suggestions = it }

flatMapLatest on Android and its counterpart on iOS automatically cancel the stale request on each new input, without manual cancellation token management.

Caching Search Suggestions

Results of popular queries are cached on the device. We use an LRU cache with 100–200 entries: on repeated input the response comes instantly from memory, without an API call. Traffic savings — from 40% to 70% for apps with recurring queries.

private val cache = object : LinkedHashMap<String, List<String>>(200, 0.75f, true) {
    override fun removeEldestEntry(eldest: Map.Entry<String, List<String>>) = size > 200
}

fun getSuggestions(query: String): List<String>? = cache[query.lowercase()]
fun putSuggestions(query: String, results: List<String>) {
    cache[query.lowercase()] = results
}

For offline access, we extend the cache to Room FTS4 on Android or CoreData on iOS — the user gets suggestions even without a network.

Search History

We store the last 10–15 queries in local storage. Display them with a clock icon above the API suggestions, de-duplicate by text. A clear history button is mandatory: users expect it.

When a suggestion from history is selected, we save the query again to update the order, then trigger a full search for the selected text.

Highlighting Matches in Results

We split the suggestion text into parts: the matching fragment is highlighted in color. On Android — SpannableString with ForegroundColorSpan, on iOS — NSAttributedString, on Flutter — RichText with TextSpan. Highlighting is case-insensitive and accounts for multiple occurrences in one line.

// iOS: highlight via NSAttributedString
func highlight(_ text: String, query: String) -> NSAttributedString {
    let attr = NSMutableAttributedString(string: text)
    var searchRange = text.startIndex..<text.endIndex
    while let range = text.range(of: query, options: .caseInsensitive, range: searchRange) {
        attr.addAttribute(.foregroundColor, value: UIColor.systemBlue,
                         range: NSRange(range, in: text))
        searchRange = range.upperBound..<text.endIndex
    }
    return attr
}

Important to handle an empty query string: when the field is empty, suggestions are not shown or only history is displayed.

What's Included in Search Development?

We perform the full cycle of work turnkey:

1. Architectural analysis: choice of approach (client-side, server-side, combined)
2. Implementation of debounce logic and request cancellation
3. Caching of search suggestions: LRU in-memory and persistent layer
4. Search history with deduplication and clear button
5. Highlighting matches on native components
6. Handling edge cases: empty query, offline, API errors
7. Testing under slow connection and without network
8. Documentation and delivery of source code with usage examples

We estimate the project for free — drop us a message, we'll calculate the cost and timeline.

From Our Practice

Our client — a building materials marketplace — complained about slow search: 1.5–2 seconds response on each character. We implemented a combined approach: fuse.js on an offline cache with 3,000 SKUs plus API for non-standard queries. Result: average response time 60 ms, search abandonment decreased by 34%, completed orders increased.

In another project — a medical app on iOS and Android — we added search history and highlighting. Time to select a drug was reduced from 8 to 4 screen touches.

Our experience — over 50 delivered mobile projects, 6 years in native and cross-platform development. We guarantee deadlines and code quality.

Timelines

The cost is determined after analysis. Leave a request — we'll calculate the timeline and cost for your project.

The standard Apple UISearchController covers basic search, but custom autocomplete gives you control over ranking algorithm, offline mode, and suggestion design.

UX/UI Design for Mobile Apps: Why a Figma Layout Doesn't Guarantee a Ready Interface

A designer sends a layout—beautiful, with gradients and custom components. The developer opens it and realizes: the button is 36pt, the tap target is 20pt. On an iPhone SE, it's physically impossible to press with a thumb. The bottom sheet covers content when the keyboard appears. Navigation is built against the native iOS model. Apple will reject the app, or users will leave within a week—depending on how lucky you get with the review.

We have been designing mobile UX/UI for over 5 years and have seen hundreds of such situations. During this time, we have designed and helped launch 30+ mobile apps—from fintech products to social networks. You don't need to guess whether the design will pass App Review or Google Play—we embed platform requirements from the first screen. We'll assess your project in one day, contact us.

Mobile UX/UI is not an adaptation of web design. It is a separate discipline with specific platform constraints: safe area, touch gestures, UIViewController lifecycle, Activity state management.

Why Can't You Ignore Human Interface Guidelines and Material Design 3?

Apple HIG and Google Material Design 3 are not aesthetic recommendations. They are documented user expectations formed by years of using system applications. Expectations confirmed by user experience research on mobile platforms (User experience design).

HIG defines: minimum tap target 44×44 pt, safe area insets for notch and Dynamic Island, standard gestures (swipe back on iOS, back gesture on Android 10+). Ignoring safe area is a common mistake. safeAreaLayoutGuide in UIKit and safeAreaPadding in SwiftUI exist precisely for this. A designer who doesn't set safe area margins in Figma guarantees a bug during development.

Material Design 3 introduced Dynamic Color—the color scheme is generated from the user's wallpaper via MaterialTheme.colorScheme in Jetpack Compose. An app that ignores dynamic colors on Android 12+ looks out of place. This is not critical for niche products but is noticeable in mass-market apps.

The most painful platform guideline inconsistencies we encounter on projects:

• Custom navigation on top of system navigation. iOS users expect swipe back from any point on the left edge of the screen. A custom NavigationController without interactive gesture breaks this. Android users expect the system back button—a custom back button in the left corner does not fully replace it.
• Modal windows instead of navigation push. Bottom sheets are appropriate for actions, not for navigating content.
• Missing haptic feedback. UIImpactFeedbackGenerator on iOS is not decoration but part of the interface response. Buttons, swipes, and confirmation actions without tactile feedback feel broken.

Table: Comparison of iOS and Android UX/UI Requirements

How to Get the Most Out of Figma?

The Figma Variables API has changed the workflow. Design tokens—colors, typography, radii, spacing—are stored as variables and exported directly to code via figma-tokens or style-dictionary. This eliminates manual value transfer and desynchronization between design and implementation. Practice shows: Figma Variables speeds up asset handoff to development by 2–3 times compared to static frames, and using design tokens reduces code transfer errors by 60%.

Auto Layout with wrap and spacing between elements allows building components that behave like flex containers. A developer opens a component and sees not a static artifact but a description of behavior at different content sizes.

Component Properties—variants, boolean toggles, instance swaps—enable building a full design system right in Figma. A button with 4 states (default, hover, pressed, disabled), 3 sizes, and 2 icon variants is one component, not 24 frames.

Figma Prototype with Variables allows creating an interactive prototype with real state: showing how the screen changes with different variable values. This is no longer just a "clickable layout" but a full UX testing tool.

How to Benefit from Prototyping and UX Testing Before Development?

The most expensive mistake in a mobile product is to develop a feature, release it, and discover that users don't understand how it works. A Figma prototype at the testing stage costs zero development hours. Redoing a finished screen costs days. Testing a prototype before development begins reduces the number of fixes by 80%.

For usability testing, we use Maze (task testing on a prototype—the user goes through a scenario, we get heatmaps and mis-click rates) or direct sessions via UserTesting. Key metrics are task completion rate and time on task, not "like/dislike."

A/B testing on mobile is harder than on web: the App Store doesn't allow UI changes without an app update. Therefore, it's important to test hypotheses on a prototype before release, not through production experiments. According to research, fixing a bug found on a prototype costs 10 times less than after production release. And average task completion time increases by 40% after proper UX optimization during prototyping.

Why Are Animations Critical for Interface Perception?

Animations in mobile apps are feedback. An element doesn't appear instantly—it transitions to the desired state over 200–350 ms. This gives the brain context to understand what happened.

• iOS: withAnimation in SwiftUI, UIViewPropertyAnimator in UIKit for interactive animations with interruption capabilities. Spring animations with dampingRatio are the basis of most Apple system transitions.
• Android: AnimatedVisibility, animateContentSize, Crossfade in Compose. MotionLayout for complex scenes with multiple transformations.
• Flutter: AnimationController + Tween, Hero animations between screens, Lottie for After Effects exports. Lottie is especially effective for onboarding illustrations and empty states.

The key constraint is 16 ms per frame (60 fps) or 8 ms (120 fps on ProMotion devices). Animations must run on the GPU via CALayer/RenderThread, not on the CPU via layoutSubviews. Profiling via Core Animation instrument in Xcode is a mandatory step before releasing animated screens.

Why Is Accessibility Not an Optional Feature?

VoiceOver on iOS and TalkBack on Android are used by up to 15% of users—this statistic is confirmed by accessibility research described in Accessibility (Wikipedia). In absolute numbers for a large app, this is thousands of people. Additionally, App Store rejections due to accessibility occur, though rarely.

Minimum checklist:

• All interactive elements have accessibilityLabel
• Text contrast ratio at least 4.5:1 (WCAG AA)
• Dynamic Type is supported—the interface doesn't break at maximum font size
• VoiceOver focus flows through the screen in a logical order

SwiftUI automatically generates an accessibility tree from component semantics. UIKit requires manual setup of accessibilityTraits, accessibilityHint, and grouping via shouldGroupAccessibilityChildren.

What Does the Work Include?

The UX/UI design deliverables include:

What Is the Process and Timeline?

Design goes through stages: research and competitive analysis → user flows and wireframes → design system → UI layouts → prototype → testing → handoff to development.

Timeline estimates:

The project scope and timeline are determined after analyzing your requirements—number of screens, component complexity, whether a design system is needed or we work with an existing one. Get a consultation for your project—contact us for a preliminary assessment. Order a complete mobile app design—we'll assess your project in one day and propose the optimal work scope.