UISearchController replacement. Relies on a couple of internal categories, helpers, etc.

SearchController.swift

//
//  SearchController.swift
//  Prefer
//
//  Created by Bryan Irace on 5/31/17.
//  Copyright © 2017 Prefer. All rights reserved.
//

import RxSwift
import RxCocoa
import SharedUI

protocol SearchResultsUpdater: class {
    func updateSearchResults(for query: String?)
    
    func returnedFromSearch(with query: String?)
}

/**
 An alternative to `UISearchController`. `UISearchController` is inflexible and seems to have lots of bugs. So, reinvent 
 the wheel we shall.
 */
final class SearchController {
    // MARK: - Subviews
    
    private lazy var dimmedView: UIView = DimmedView().usingAutoLayout()
    
    // MARK: - Mutable
    
    /**
     Not passed into the initializer since in many cases, this will be the object that owns the search controller, 
     meaning the search controller will be lazily-instantiated.
     */
    weak var searchResultsUpdater: SearchResultsUpdater?
    
    // MARK: - Inputs
    
    private let searchResultsViewController: UIViewController
    private unowned let textField: UITextField
    private unowned let parentViewController: UIViewController
    private unowned let containingScrollView: UIScrollView
    
    // MARK: - Initialization
    
    /// Create a new instance
    ///
    /// - Parameters:
    ///   - searchResultsViewController: View controller to display results in
    ///   - textField: Text field used to drive searches
    ///   - parentViewController: View controller to be the parent of the search results view controller
    ///   - containingScrollView: Scroll view that the text field is contained by (e.g. a table that the tet field it is 
    ///     the header of). Scrolling will be disabled when the results are being shown.
    init(
        searchResultsViewController: UIViewController,
        textField: UITextField,
        parentViewController: UIViewController,
        containingScrollView: UIScrollView
    ) {
        self.searchResultsViewController = searchResultsViewController
        self.textField = textField
        self.parentViewController = parentViewController
        self.containingScrollView = containingScrollView
        
        setUpObservers()
    }
    
    // MARK: - Private
    
    private func setUpObservers() {
        _ = textField
            .rx
            .text
            .distinctUntilChanged({ (lhs, rhs) -> Bool in
                lhs == rhs
            })
            .subscribe(onNext: { [weak self] query in
                self?.searchResultsUpdater?.updateSearchResults(for: query)
            })

        _ = Observable
            .combineLatest(
                textField.rx.hasText,
                textField.rx.isEditing
            )
            .map({ (hasQuery, isEditing) in
                hasQuery || isEditing
            })
            .distinctUntilChanged()
            .subscribe(onNext: { [weak self] showResults in
                if showResults {
                    self?.showSearchResultsViewController()
                }
                else {
                    self?.hideSearchResultsViewController()
                }
            })

        _ = textField
            .rx
            .controlEvent(.editingDidEndOnExit)
            .subscribe(onNext: { [weak self] in
                self?.searchResultsUpdater?.returnedFromSearch(with: self?.textField.text)
            })
    }
    
    private func showSearchResultsViewController() {
        containingScrollView.isScrollEnabled = false
        
        parentViewController.view.addSubview(dimmedView)
        pinToParent(dimmedView)
        dimmedView.hideAndFadeIn()
        
        parentViewController.addChildViewController(searchResultsViewController)
        parentViewController.view.addSubview(searchResultsViewController.view)
        searchResultsViewController.didMove(toParentViewController: parentViewController)
        searchResultsViewController.view.translatesAutoresizingMaskIntoConstraints = false
        pinToParent(searchResultsViewController.view)
    }
    
    private func pinToParent(_ view: UIView) {
        NSLayoutConstraint.activate([
            view.topAnchor.constraint(equalTo: textField.bottomAnchor),
            view.leftAnchor.constraint(equalTo: parentViewController.view.leftAnchor),
            view.bottomAnchor.constraint(equalTo: parentViewController.bottomLayoutGuide.topAnchor),
            view.rightAnchor.constraint(equalTo: parentViewController.view.rightAnchor),
        ])
    }
    
    private func hideSearchResultsViewController() {
        dimmedView.removeFromSuperview()
        
        searchResultsViewController.willMove(toParentViewController: nil)
        searchResultsViewController.view.removeFromSuperview()
        searchResultsViewController.removeFromParentViewController()
        
        containingScrollView.isScrollEnabled = true
    }
}