Question

我正在尝试在Swift中对不同NSManagedObjects的数组进行排序。在Objective-C中，它只需要2行代码（排序描述符和实际排序）。但是，我能想出如何在swift中完成它的唯一方法就是需要几行代码。有没有比我写的代码更好和/或更快的方式？：

var orderMOs = [NSManagedObject]()
orderMOs.append(contentsOf: incidentMOs)
orderMOs.append(contentsOf: transferMOs)

orderMOs.sort (by: {(leftMO, rightMO) -> Bool in

   var leftDate: NSDate?
   var rightDate: NSDate?

   if leftMO is Incident {leftDate = (leftMO as! Incident).createdDate}
   else if leftMO is Transfer {leftDate = (leftMO as! Transfer).createdDate}

   if rightMO is Incident {rightDate = (rightMO as! Incident).createdDate}
   else if rightMO is Transfer {rightDate = (rightMO as! Transfer).createdDate}

   if leftDate == nil || rightDate == nil {return true}

   return leftDate!.compare(rightDate! as Date) == .orderedDescending
})

Answer 1

您的两个类都应该符合声明createdDate的协议。请输入orderMOs。比你不需要条件演员。

import Foundation

class A {

    init(created createdDate: Date) {
        self.createdDate = createdDate
    }
    let createdDate: Date
}


class B {
    init(created createdDate: Date) {
        self.createdDate = createdDate
    }
    var createdDate: Date
}

protocol Created {
    var createdDate: Date { get }
}


extension A: Created {}
extension B: Created {}

func createDate(year: Int, month: Int, day: Int) -> Date {
    var comps = DateComponents()
    comps.year = year
    comps.month = month
    comps.day = day
    return Calendar.current.date(from: comps)!
}


var objects = [Created]()

objects.append(A(created: createDate(year: 2018, month: 2, day: 1)))
objects.append(B(created: createDate(year: 2017, month: 12, day: 1)))
objects.append(B(created: createDate(year: 2018, month: 5, day: 18)))
objects.append(A(created: Date()))

将其排序为

objects.sort { (c1, c2) -> Bool in
    return c1.createdDate < c2.createdDate
}

您可以做的另一件事是使用带有pattern matching的switch语句来清理代码。

Answer 2

为什么不在这里使用KVC？

if let leftDate = leftMO.value(forKey: "createdDate") as? Date, 
   let rightDate = rightMO.value(forKey: "createdDate") as? Date {

    if leftDate == nil || rightDate == nil {return true}
    return leftDate.compare(rightDate) == . orderedDescending
}

最佳实践 - 在Swift中对混合对象进行排序

2 个答案: