使用swift开发ios的时候把业务可以写入到属性观察器，我也挺喜欢叫钩子函数

    var currentIndex:Int?{
        didSet{
            if currentIndex != 3{
                titleViewCells![currentIndex!].focusCell()
                titleViewCells!.filter{$0.data?.index != currentIndex}.forEach{$0.blurCell()}
                if let scrollview = scrollerContainer {
                    //滚动,切换子控制器
                    var offset = scrollview.contentOffset
                    offset.x = CGFloat(currentIndex!) * scrollview.width
                    scrollview.setContentOffset(offset, animated: true)
                }
            }else{
               forwardPage()
            }
        }
    }

currentIndex是子控制器容器的索引，他的更新会引起子控制器的切换，其实这个实现完全可以在属性setter函数重写（重载也可以）

class People(name:String,about:String){
    type  observer = (Int) => Unit
    private var privateAge = 0
    def age = {privateAge}
    def age_(willSet:observer=(newage:Int)=>{println(s"willSet ${newage}")},
             newValue: Int,
             didSet:observer=(newage:Int)=>{println(s"didSet ${newage}")}):Unit= {
                willSet(newValue);
                privateAge = newValue
                didSet(newValue);
    }
}
object KVOObject{
    def main(args: Array[String]): Unit = {
        val p = new People("twp","programer")
            p.age_(
                (newage:Int)=>{
                        println(s"newage is ${newage} and willSet")
                        println(s"age oldval is ${p.age}")
                    },
                26,
                (newage:Int)=>{
                    println(s"newage is ${newage} and didSet")
                    println(s"age  is ${p.age}")
                })
        p.age_(newValue = 26) }
}

这来实现组装的回调来编写业务处理还是很方便的。（第一次写简书，多多见谅）