Displaying searchable content by using a search controller

At a glance

Project structure

TableSearch/
├── MainTableViewController.swift
├── MainTableViewController+DataSource.swift
├── MainTableViewController+Updating.swift
├── MainTableViewController+Restore.swift
├── ResultsTableController.swift
├── DetailViewController.swift
├── Product.swift
└── Base.lproj/MainStoryboard.storyboard

Structure observations

• File suffixes divide one controller by responsibility without creating extra owners.
• ResultsTableController is intentionally presentation-only; filtering stays with the main controller that owns the complete product array.
• Product is in a model file because both table controllers and state restoration use it.

Overall architecture

flowchart LR
    Catalog["MainTableViewController.products"] --> MainTable["Main table sections"]
    SearchBar["UISearchBar text and scope"] --> Search["UISearchResultsUpdating"]
    Catalog --> Search
    Search --> Predicate["NSCompoundPredicate"]
    Predicate --> Filtered["filteredProducts"]
    Filtered --> Results["ResultsTableController"]
    MainTable --> Selection["MainTableViewController selection"]
    Results --> Selection
    Selection --> Detail["DetailViewController"]
    Restore["NSCoder state"] --> SearchBar

Reference code

TableSearch/MainTableViewController+Updating.swift:99 — the updater derives a filtered projection and gives it to the results controller.

func updateSearchResults(for searchController: UISearchController) {
    // Update the filtered array based on the search text.
    let searchResults = products

    // Strip out all the leading and trailing spaces.
    let whitespaceCharacterSet = CharacterSet.whitespaces
    let strippedString =
        searchController.searchBar.text!.trimmingCharacters(in: whitespaceCharacterSet)
    let searchItems = strippedString.components(separatedBy: " ") as [String]

    let andMatchPredicates: [NSPredicate] = searchItems.map { searchString in
        findMatches(searchString: searchString)
    }

    let finalCompoundPredicate =
        NSCompoundPredicate(andPredicateWithSubpredicates: andMatchPredicates)

    let filteredResults = searchResults.filter { finalCompoundPredicate.evaluate(with: $0) }

    if let resultsController = searchController.searchResultsController as? ResultsTableController {
        resultsController.filteredProducts = filteredResults
        resultsController.tableView.reloadData()
    }
}

Interpretation

The full catalog remains the source of truth. Search results are replaceable view state, recalculated from current text and scope rather than mutated back into the source array.

Ownership and state

classDiagram
    MainTableViewController *-- UISearchController : creates
    MainTableViewController *-- ResultsTableController : storyboard reference
    MainTableViewController *-- Product : owns catalog array
    MainTableViewController *-- SearchControllerRestorableState : owns pending flags
    UISearchController o-- ResultsTableController : presents
    ResultsTableController o-- Product : filtered array references
    MainTableViewController --> DetailViewController : creates and pushes
    DetailViewController o-- Product : selected model
    Product ..|> Codable

Ownership evidence

TableSearch/MainTableViewController.swift:36 — the main controller wires and retains the complete search presentation graph.

resultsTableController = storyboard?.instantiateViewController(
    withIdentifier: "ResultsTableController") as? ResultsTableController
resultsTableController.tableView.delegate = self

searchController = UISearchController(searchResultsController: resultsTableController)
searchController.delegate = self
searchController.searchResultsUpdater = self
searchController.searchBar.delegate = self
navigationItem.searchController = searchController

Class and protocol design

No app-defined protocol is present. UIKit protocols provide event seams: UISearchResultsUpdating transforms query state, search delegates report UI changes, and table delegates route selection.

Access control

Reference code

TableSearch/Product.swift:49 — model fields are exposed to the Objective-C runtime specifically for predicate key paths.

@objc var title: String
@objc var yearIntroduced: Int
@objc var introPrice: Double
@objc var type: Int

Logic ownership and placement

Design patterns

Naming conventions

• Main..., Results..., and Detail... communicate navigation roles.
• filteredProducts distinguishes derived state from source products.
• RestorationKeys and SearchControllerRestorableState separate serialized keys from temporary replay flags.
• Capability files use +DataSource, +Updating, and +Restore suffixes.

Architecture takeaways

• Keep query results as a projection of source data rather than a second authoritative model.
• Let one coordinator own UISearchController, its results screen, and navigation routing.
• When splitting a type across files, accept internal access deliberately and keep truly local helpers private.
• Restore first-responder and presentation state at a lifecycle point where the hierarchy exists.

Source map

• Official Apple documentation