// 程序启动完成func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {// Override point for customization after application launch.self.window = UIWindow (frame: UIScreen.main.bounds)self.window?.rootViewController = UINavigationController (rootViewController: ViewController())self.window?.makeKeyAndVisible()USER_DEFAULTS .set(false, forKey: ISQRCONTROLLER)return true}
// 正在使用应用的时候按“home”键，恢复系统的亮度func applicationWillResignActive(_ application: UIApplication) {let brights:float_t = USER_DEFAULTS .value(forKey: SCREEN_BRIGHT) as! Floatprint("当前亮度00： \(brights)")UIScreen.main.brightness = CGFloat(brights)}
//  应用成前台运行的时候，（即上次再使用APP的时候，突然按“home”键后，过一定时间又想用APP，如果是从二维码页面退出到后台，需要使二维码页面变亮（这时二维码的控制器中的几个方法不起作用，就靠这里了））func applicationDidBecomeActive(_ application: UIApplication) {let isQR = Bool(USER_DEFAULTS .value(forKey: ISQRCONTROLLER) as! Bool)if isQR {UIScreen.main.brightness = 0.6}else{USER_DEFAULTS .set(UIScreen.main.brightness, forKey: SCREEN_BRIGHT)}}

// ViewController.swift
import UIKitclass ViewController: UIViewController {override func viewDidLoad() {super.viewDidLoad()self.view.backgroundColor = UIColor .whitelet qRBtn:UIButton = UIButton (frame: CGRect(x: 60, y:100, width: 90, height: 30))qRBtn.layer.borderColor = UIColor .blue.cgColorqRBtn.layer.borderWidth = 1.0qRBtn.layer.cornerRadius = 5.0qRBtn.layer.masksToBounds = trueqRBtn .setTitle("我的二维码", for: UIControlState.normal)qRBtn.titleLabel?.font = UIFont .systemFont(ofSize: 14)qRBtn .setTitleColor(UIColor.blue, for: UIControlState.normal)qRBtn .addTarget(self, action: #selector(ViewController.btnClick), for: UIControlEvents.touchUpInside)self.view .addSubview(qRBtn)}@objc func btnClick() -> Void {self.navigationController?.pushViewController(QRCodeController(), animated: true)}override func didReceiveMemoryWarning() {super.didReceiveMemoryWarning()// Dispose of any resources that can be recreated.}}

//  Created by Lijinkui on 2017/10/25.
//  Copyright © 2017 year Lijinkui. All rights reserved.
//import UIKitpublic let ScreenW = UIScreen.main.bounds.width
public let ScreenH = UIScreen.main.bounds.height
public let USER_DEFAULTS = UserDefaults.standard
public let SCREEN_BRIGHT = "screenBrights"
public let ISQRCONTROLLER = "isQRController"
var currentLight: CGFloat = 0;
class QRCodeController: UIViewController {override func viewDidLoad() {super.viewDidLoad()self .title = "我的二维码"self.view?.backgroundColor = UIColor .whitelet qrImg: UIImageView = UIImageView (frame: CGRect(x: ScreenW * 0.1, y: ScreenH/2 - (ScreenW*0.4), width: ScreenW * 0.8, height: ScreenW * 0.8))qrImg.image = UIImage (named: "CodeImg")self.view?.addSubview(qrImg)}// 把将要进入二维码页面时的系统亮度保存override func viewWillAppear(_ animated: Bool) {currentLight = CGFloat(USER_DEFAULTS .value(forKey: SCREEN_BRIGHT) as! Float)USER_DEFAULTS .set(true, forKey: ISQRCONTROLLER)}// 进入控制器完成后，让控制器高亮override func viewDidAppear(_ animated: Bool) {UIScreen.main .brightness = 0.6}// 退出控制器时恢复之前的亮度  override func viewWillDisappear(_ animated: Bool) {UIScreen.main.brightness = currentLightUSER_DEFAULTS .set(false, forKey: ISQRCONTROLLER)}override func didReceiveMemoryWarning() {super.didReceiveMemoryWarning()// Dispose of any resources that can be recreated.}}