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Day 24

  • Projects 4, Part two
    • Monitoring page loads: UIToolbar and UIProgressView
    • Refactoring for the win

Monitoring page loads: UIToolbar and UIProgressView

UIToolBar

  • UIBarButtonItem collection 을 갖고 있음
  • viewDidLoad에 UIBarButtonItem을 만들고 toolbarItems에 array의 item으로 추가함
let spacer = UIBarButtonItem(barButtonSystemItem: .flexibleSpace, target: nil, action: nil)
let refresh = UIBarButtonItem(barButtonSystemItem: .refresh, target: webView, action: #selector(webView.reload))
    
toolbarItems = [progressButton, spacer, refresh]
navigationController?.isToolbarHidden = false

UIProgressView

  • "progress bar"라고 불림
  • 진행 사항을 보여주는 뷰(blue color on gray background, from left to right)

class에 아래와 같이 추가함

var progressView: UIProgressView!

viewDidLoad에 아래와 같이 추가함

progressView = UIProgressView(progressViewStyle: .default)
progressView.sizeToFit()
let progressButton = UIBarButtonItem(customView: progressView)

toolBarItems에 추가

toolbarItems = [progressButton, spacer, refresh]

KVO(Key-Value-Observing)

  • Please tell me when the property X of object Y gets changed by anyone at any time
webView.addObserver(self, 
					forKeyPath: #keyPath(WKWebView.estimatedProgress), 
 					options: .new, 
					context: nil)
  • addObserver() 메서드는 4개의 parameter를 갖음
  • viewController가 observer임 (self)
  • WKWebView의 estimatedProgress property를 obsrve함.
  • forKeyPath와 context좀 더 설명
  • forKeyPath는 forProperty로 명명되지 않음. 속성이름이 아님, 실제 경로를 지정할 수 있음. 하나의 속성을 다른 속성에 포함하거나 다른 속성을 다른 속성에 포함할 수 있음. 고급 키 경로를 사용하면 배열의 모든 요소를 평균화하는 등의 기능을 추가 할 수도 있음.
  • WKWebView class에는 estimatedProgress속성이 있음
  • context는 더 쉬움. 고유한 값을 제공하면 값이 변경되었다는 알림을 받을 때 동일한 context 값이 다시 전송됨. 이렇게 하면 컨텍스트를 점검하여 호출 된 옵저버인지 확인할 수 있음.
  • Warning: 복잡한 앱에서, addOberver()를 할경우 removeObserver를 해야 함, observing이 끝날 때.
override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
	if keyPath == "estimatedProgress" {
		progressView.progress = Float(webView.estimatedProgress)
	}
}

Refactoring for the win

//
//  ViewController.swift
//  Project4
//
//  Created by dave76 on 12/06/2019.
//  Copyright © 2019 dave76. All rights reserved.
//

import UIKit
import WebKit

class ViewController: UIViewController, WKNavigationDelegate {
  
  // MARK:- Properties
  
  var webView: WKWebView!
  var progressView: UIProgressView!
  var websites = ["apple.com", "hackingwithswift.com"]
  
  override func loadView() {
    webView = WKWebView()
    webView.navigationDelegate = self
    view = webView
  }

  // MARK:- View Life Cycle
  
  override func viewDidLoad() {
    super.viewDidLoad()
    
    navigationItem.rightBarButtonItem = UIBarButtonItem(title: "Open", style: .plain, target: self, action: #selector(openTapped))
    let spacer = UIBarButtonItem(barButtonSystemItem: .flexibleSpace, target: nil, action: nil)
    let refresh = UIBarButtonItem(barButtonSystemItem: .refresh, target: webView, action: #selector(webView.reload))
    
    progressView = UIProgressView(progressViewStyle: .default)
    progressView.sizeToFit()
    let progressButton = UIBarButtonItem(customView: progressView)

    toolbarItems = [progressButton, spacer, refresh]
    navigationController?.isToolbarHidden = false
    
    webView.addObserver(self, forKeyPath: #keyPath(WKWebView.estimatedProgress), options: .new, context: nil)
    
    
    guard let url = URL(string: "https://" + websites[0]) else { return }
    webView.load(URLRequest(url: url))
    webView.allowsBackForwardNavigationGestures = true
  }
  
  // MARK:- Methods
  
  @objc func openTapped() {
    let ac = UIAlertController(title: "Open page...", message: nil, preferredStyle: .actionSheet)
    
    for website in websites {
      ac.addAction(UIAlertAction(title: website, style: .default, handler: openPage))
    }
    
    ac.addAction(UIAlertAction(title: "Cancel", style: .cancel))
    ac.popoverPresentationController?.barButtonItem = navigationItem.rightBarButtonItem
    present(ac, animated: true)
  }
  
  func openPage(action: UIAlertAction) {
    guard let actionTitle = action.title else { return }
    guard let url = URL(string: "https://" + actionTitle) else { return }
    webView.load(URLRequest(url: url))
  }
  
  func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {
    title = webView.title
  }
  
  override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
    if keyPath == "estimatedProgress" {
      progressView.progress = Float(webView.estimatedProgress)
    }
  }
  
  func webView(_ webView: WKWebView, decidePolicyFor navigationAction: WKNavigationAction, decisionHandler: @escaping (WKNavigationActionPolicy) -> Void) {
    let url = navigationAction.request.url
    
    if let host = url?.host {
      for website in websites {
        if host.contains(website) {
          decisionHandler(.allow)
          return
        }
      }
    }
    decisionHandler(.cancel)
  }
}