Various search bar implementations. Including an RxSwift / reactive swift version too

appleSearchBarSample.swift

//https://developer.apple.com/library/content/samplecode/TableSearch_UISearchController/Introduction/Intro.html    

// MARK: - UISearchResultsUpdating
    
    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]
        
        // Build all the "AND" expressions for each value in the searchString.
        let andMatchPredicates: [NSPredicate] = searchItems.map { searchString in
            // Each searchString creates an OR predicate for: name, yearIntroduced, introPrice.
            //
            // Example if searchItems contains "iphone 599 2007":
            //      name CONTAINS[c] "iphone"
            //      name CONTAINS[c] "599", yearIntroduced ==[c] 599, introPrice ==[c] 599
            //      name CONTAINS[c] "2007", yearIntroduced ==[c] 2007, introPrice ==[c] 2007
            //
            var searchItemsPredicate = [NSPredicate]()
            
            // Below we use NSExpression represent expressions in our predicates.
            // NSPredicate is made up of smaller, atomic parts: two NSExpressions (a left-hand value and a right-hand value).
            
            // Name field matching.
            let titleExpression = NSExpression(forKeyPath: "title")
            let searchStringExpression = NSExpression(forConstantValue: searchString)
            
            let titleSearchComparisonPredicate = NSComparisonPredicate(leftExpression: titleExpression, rightExpression: searchStringExpression, modifier: .direct, type: .contains, options: .caseInsensitive)
            
            searchItemsPredicate.append(titleSearchComparisonPredicate)
            
            let numberFormatter = NumberFormatter()
            numberFormatter.numberStyle = .none
            numberFormatter.formatterBehavior = .default
            
            let targetNumber = numberFormatter.number(from: searchString)
            
            // `searchString` may fail to convert to a number.
            if targetNumber != nil {
                // Use `targetNumberExpression` in both the following predicates.
                let targetNumberExpression = NSExpression(forConstantValue: targetNumber!)
                
                // `yearIntroduced` field matching.
                let yearIntroducedExpression = NSExpression(forKeyPath: "yearIntroduced")
                let yearIntroducedPredicate = NSComparisonPredicate(leftExpression: yearIntroducedExpression, rightExpression: targetNumberExpression, modifier: .direct, type: .equalTo, options: .caseInsensitive)
                
                searchItemsPredicate.append(yearIntroducedPredicate)
                
                // `price` field matching.
                let lhs = NSExpression(forKeyPath: "introPrice")
                
                let finalPredicate = NSComparisonPredicate(leftExpression: lhs, rightExpression: targetNumberExpression, modifier: .direct, type: .equalTo, options: .caseInsensitive)
                
                searchItemsPredicate.append(finalPredicate)
            }
            
            // Add this OR predicate to our master AND predicate.
            let orMatchPredicate = NSCompoundPredicate(orPredicateWithSubpredicates:searchItemsPredicate)
            
            return orMatchPredicate
        }
        

rxswift.swift

// https://www.thedroidsonroids.com/blog/ios/rxswift-by-examples-1-the-basics/
// wow that's pretty  clean
searchBar
    .rx.text // Observable property thanks to RxCocoa
    .orEmpty // Make it non-optional
    .debounce(0.5, scheduler: MainScheduler.instance) // Wait 0.5 for changes.
    .distinctUntilChanged() // If they didn't occur, check if the new value is the same as old.
    .filter { !$0.isEmpty } // If the new value is really new, filter for non-empty query.
    .subscribe(onNext: { [unowned self] query in // Here we subscribe to every new value, that is not empty (thanks to filter above).
        self.shownCities = self.allCities.filter { $0.hasPrefix(query) } // We now do our "API Request" to find cities.
        self.tableView.reloadData() // And reload table view data.
    })
    .addDisposableTo(disposeBag)

You nailed it with rx example, thanks a lot!