在Swift中使用引用设置NSArray实例

Question

I'm trying to set the values for NSArray using reference in Swift but can't seem to get it working.

var list = self.isFiltered ? self.filteredEventsList : self.eventsList
self.sortTableViewForEventName(&list)

Then:

private func sortTableViewForEventName(inout eventArray: NSArray) {

        let sortedEvents = eventArray.sortedArrayUsingComparator({ (firstEvent, secondEvent) in

            let firstEventName = (firstEvent as! Event).name
            let secondEventName = (secondEvent as! Event).name

            return firstEventName.compare(secondEventName)
        })

        eventArray = sortedEvents
    }

The change in eventArray does not reflect in eventsList or filteredEventsList, whichever may be applicable.

Answer 1

It would be much easier in this case to use a Swift array [Event] you can then sort and filter something like this...

private func sortedEventsByName(events: [Event]) -> [Event] {
    return events.sort {
        $0.name > $1.name
    }
}

What would be even simpler is to create an extension on Event like so...

extension Event: Comparable {}

func == (lhs: Event, rhs: Event) -> Bool {
    return lsh.name == rhs.name
}

func < (lhs: Event, rhs: Event) -> Bool {
    return lhs.name < rhs.name
}

Then you can just use sort like this...

let sortedEvents = events.sort(<)

and

let filteredEvents = events.filter {
    $0.name == someFilterName
}

Answer 2

You need to have a really good reason for using inout parameters, and in this case I don't think you have one. You can simply have your function return the sorted array:

private func sortTableViewForEventName(eventArray: NSArray) -> NSArray {
    let sortedEvents = eventArray.sortedArrayUsingComparator({ (firstEvent, secondEvent) in

        let firstEventName = (firstEvent as! Event).name
        let secondEventName = (secondEvent as! Event).name

        return firstEventName.compare(secondEventName)
    })

    return sortedEvents
}

then you would say

var list = self.isFiltered ? self.filteredEventsList : self.eventsList
list = self.sortTableViewForEventName(list)

But, unless you have a good reason for using NSArray , you can just use a Swift array and gain type awareness/safety and more concise sorting:

private func sortTableViewForEventName(eventArray: [Event]) -> [Event] {
    let sortedEvents = eventArray.sort {
        $0.name < $1.name
    }
    return sortedEvents
 }

Answer 3

What you give to sortTableViewForEventName is a reference to list , and NSArray is immutable, so the only thing you modify is the local variable list .

you might try this :

var list = self.isFiltered ? self.filteredEventsList : self.eventsList
self.sortTableViewForEventName(&list)
if self.isFiltered {
  self.filteredEventsList = list
} else {
  self.eventsList = list
}

or this (not sure if it works) :

self.sortTableViewForEventName(self.isFiltered ? &self.filteredEventsList : &self.eventsList)

or make filteredEventsList and eventsList NSMutableArray, but it's probably not a good idea, because it would break encapsulation.