KVO最佳实践

数据源状态机：

import Foundation

enum ProviderState {
    case idle
    case loading
    case submit
    case failed(_ message:String)
}

数据源基类：

import Foundation
@objcMembers class ProviderObject: NSObject {
    var state:ProviderState? {
        didSet {
            stateMonitor = !stateMonitor
        }
    }
    var noMoreData:Bool = false
  
    dynamic var stateMonitor: Bool = false
}

使用方法：监听数据源的stateMonitor属性，如果有改变，则手动去获取实际数据、state状态等；优点：

• 可以绕开关联性枚举值无法通过observe监听的问题
• 只需要监听一个属性

测试类：

class DemoProvider: ProviderObject {
	var dogAges:[Int] = []
    var catAges:[Int] = []
}

KVO实现

var ob: NSKeyValueObservation?

func setupKVO() {
        ob = DemoProvider.observe(\.stateMonitor, changeHandler: { (demo, value) in
            switch demo.state {
             case idle:
             	//reload data
             case loading:
             	//show loading animation
             ....
            }
        })    }