Swift 使用 Observe 监测页面滚动的实现方法

Swift 以前是通过addObserver来实现对某个属性的变化监听，而最新的变化，书写起开更加方便。

									observer = test.observe(\.field, options: [.new, .initial]) { (object, change) in

									   print(change)

									  }

一定要用属性赋值当前的 observe 结果，没有的话可能会造成 change 不生效。

对 UIScrollView 的滚动监听，我们可以使用UIScrollViewDelegate

									extension UIScrollViewDelegate{

									 func scrollViewDidScroll(scrollView: UIScrollView){

									  //do something

									 }

									}

这里推荐使用 Observe 比较方便的是可以进行模块的逻辑的拆分，我们只需在自己的组件里面进行监听

									class ComponetView: UIVIew {

									    private var observation: NSKeyValueObservation?

									    init(targetView: UIView) {

									        observation = targetView.observe(\.contentOffset, options: [.new]) { [weak self] scrollView, change in

									   // handle data contentOffset

									  }

									    }

									}

附录：Swift中实现Observable机制

今天给别人讲个Observable的实现和使用场景，结合Observable-Swiftgithub:https://github.com/slazyk/Observable-Swift讲了半天貌似还没有特别明白，故写了个简易的实现，讲述了下Observable属性监控机制。

									//: Playground - noun: a place where people can play

									import UIKit

									import Foundation

									// MARK: - Observable

									class Observable<T> {

									  // 定义block结构

									  typealias Observer = T -> Void

									  // 申明一个block，用于数据改变的执行

									  private var observer: Observer?

									  // 数据发生变更，则通过observer告知

									  var value: T {

									    didSet {

									      observer?(value)

									    }

									  }

									  init(_ v: T) {

									    value = v

									  }

									  func observe(observer: Observer?) {

									    self.observer = observer

									    observer?(value)

									  }

									}

									// MARK: - People

									struct PeopleModel {

									  let firstName: Observable<String>

									  let lastName: Observable<String>

									  init(firstName: String, lastName: String) {

									    self.firstName = Observable(firstName)

									    self.lastName = Observable(lastName)

									  }

									}

									// MARK: - Test

									// test1

									let people = PeopleModel(firstName: "sunny", lastName: "liu")

									people.firstName.observe {

									  newValue in

									  print("firstName changed: \(newValue)")

									}

									people.lastName.observe {

									  print("lastName changed: \($0)")

									}

									people.firstName.value = "sunny2"

									people.lastName.value = "liu2"

									// test2

									class House {

									  let lableHouseName = UILabel()

									  init() {

									  }

									  var people: PeopleModel? {

									    didSet {

									      people?.firstName.observe{

									        [unowned self] in

									        self.lableHouseName.text = $0

									      }

									    }

									  }

									}