ios - 在自定义类中初始化日期会导致错误 : "instance member cannot be used on type"

Question

我发现了一些其他问题，但没有一个解决方案有效，也许我的情况在某些关键方面有所不同。代码如下:

class ToDoList {

    let date = NSDate()
    let calendar = NSCalendar.currentCalendar()
    let components = calendar.components([.Day , .Month , .Year], fromDate: date)

    let dateCreated : Int = components.year*10_000 + components.month*100 + components.day  //TD: take YYYYMMDD from NSDate each initialization
    ...
}

XCode 错误:

"Instance member 'calendar' cannot be used on type 'ToDoList'.

我尝试将组件实现为带有 getter 的变量，但没有成功。

谢谢!

Answer 1

您不能根据其他实例变量的值在类的顶层声明属性或实例变量。

您可以使用计算属性

class ToDoList {

  var dateCreated : Int {
    let date = NSDate()
    let calendar = NSCalendar.currentCalendar()
    let components = calendar.components([.Day , .Month , .Year], fromDate: date)
    return components.year * 10_000 + components.month * 100 + components.day
  }

}

或者惰性实例化变量

class ToDoList {

  lazy var dateCreated : Int = {
    let date = NSDate()
    let calendar = NSCalendar.currentCalendar()
    let components = components([.Day , .Month , .Year], fromDate: date)
    return components.year * 10_000 + components.month * 100 + components.day
  }()

}