[Throttling] #throttling #SearchBar

SearchBar.swift

import UIKit

public class SearchBar: UISearchBar, UISearchBarDelegate {
	
	/// Throttle engine
	private var throttler: Throttler? = nil
	
	/// Throttling interval
	public var throttlingInterval: Double? = 0 {
		didSet {
			guard let interval = throttlingInterval else {
				self.throttler = nil
				return
			}
			self.throttler = Throttler(seconds: interval)
		}
	}
	
	/// Event received when cancel is pressed
	public var onCancel: (() -> (Void))? = nil
	
	/// Event received when a change into the search box is occurred
	public var onSearch: ((String) -> (Void))? = nil
	
	public override func awakeFromNib() {
		super.awakeFromNib()
		self.delegate = self
	}
	
	// Events for UISearchBarDelegate
	
	public func searchBarCancelButtonClicked(_ searchBar: UISearchBar) {
		self.onCancel?()
	}
	
	public func searchBarSearchButtonClicked(_ searchBar: UISearchBar) {
		self.onSearch?(self.text ?? "")
	}
	
	public func searchBar(_ searchBar: UISearchBar, textDidChange searchText: String) {
		guard let throttler = self.throttler else {
			self.onSearch?(searchText)
			return
		}
		throttler.throttle {
			DispatchQueue.main.async {
				self.onSearch?(self.text ?? "")
			}
		}
	}
	
}

Throttler.swift

//  Throttler.swift
//
//  Created by Daniele Margutti on 10/19/2017
//
//  web: http://www.danielemargutti.com
//  email: hello@danielemargutti.com
//
//  Updated by Ignazio Calò on 19/10/2017.
 
import UIKit
import Foundation
 
public class Throttler {
    
    private let queue: DispatchQueue = DispatchQueue.global(qos: .background)
    
    private var job: DispatchWorkItem = DispatchWorkItem(block: {})
    private var previousRun: Date = Date.distantPast
    private var maxInterval: Int
    
    init(seconds: Int) {
        self.maxInterval = seconds
    }
    
    
    func throttle(block: @escaping () -> ()) {
        job.cancel()
        job = DispatchWorkItem(){ [weak self] in
            self?.previousRun = Date()
            block()
        }
        let delay = Date.second(from: previousRun) > maxInterval ? 0 : maxInterval
        queue.asyncAfter(deadline: .now() + Double(delay), execute: job)
    }
}
 
private extension Date {
    static func second(from referenceDate: Date) -> Int {
        return Int(Date().timeIntervalSince(referenceDate).rounded())
    }
}

ViewController.swift

// value to search for an interval >= 0.5 seconds.
searchBar.throttlingInterval = 0.5
 
// Receive events for search
searchBar.onSearch = { text in
  if text.length == 0 { // user tapped the 'X' button
    // restore our plain list without search filter
  } else if textToSearch.length > MIN_CHARS_TO_SEARCH {
   // A valid search (where length > MIN_CHARS_TO_SEARCH) must be
   // performed.
  }
}