快速替换旧式枚举

Question

Back in the old Objective-C days I would often use enums for things like tables with constant contents, segmented controls, etc - in situations where there was an enforced incremented list of integers starting at zero. I would also often add a ...count member at the end to give a count of the entries, useful for table section & rows. Trying to do this with swift enums is proving troublesome - lots of conversions to & from raw values and extra default clauses in switches to allow for the 'count' entry. Can anyone suggest a graceful method of dealing with these sorts of situations?

Answer 1

Automatic increment is still available in Swift.

enum Section: Int {
   case A = 0
   case B
   case C
}

Section.C.rawValue // -> 2

As for count , you should implement it manually (as How do I get the count of a Swift enum? ):

enum Section: Int {
   case A = 0
   case B
   case C

   static let count = C.rawValue + 1
}

As for "conversions to & from raw values and extra default clauses" problem, compare with enum instead of its rawValue .

func numberOfSectionsInTableView(tableView: UITableView) -> Int {
    return Section.count
}

func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    switch Section(rawValue: section)! {
    case .A: return 1
    case .B: return 2
    case .C: return 5
    }
}

If you want to do something like array[Section.A] , you can easily implement it.

extension Array {
    subscript(section: Section) -> T {
        return self[section.rawValue]
    }
}

extension NSIndexPath {
    convenience init(forRow row: Int, inSection section: Section) {
        self.init(forRow: row, inSection: section.rawValue)
    }
}

let array = ["foo", "bar", "baz"]
array[.B] // -> "bar"


let indexPath = NSIndexPath(forRow: 20, inSection: .C)
indexPath.section // -> 2
indexPath.row // -> 20

And so on.. :)

Answer 2

Add a function "count" to each enum. For example

static func count() -> Int { return 3 }

Integer -> enum conversion is done by the init method.