问题:

I converted an NSIndexSet to an [Int] array using the answer at https://stackoverflow.com/a/28964059/6481734 I need to do essentially the opposite, turning the same kind of array back into an NSIndexSet.

回答1:

Swift 3

IndexSet can be created directly from an array literal using init(arrayLiteral:), like so:

let indices: IndexSet = [1, 2, 3]

Original answer (Swift 2.2)

Similar to pbasdf's answer, but uses forEach(_:)

let array = [1,2,3,4,5,7,8,10]

let indexSet = NSMutableIndexSet()
array.forEach(indexSet.add) //Swift 3
//Swift 2.2: array.forEach{indexSet.addIndex($0)}

print(indexSet)

回答2:

This will be a lot easier in Swift 3:

let array = [1,2,3,4,5,7,8,10]
let indexSet = IndexSet(array)

Wow!

回答3:

Swift 3+

let fromRange = IndexSet(0...10)
let fromArray = IndexSet([1, 2, 3, 5, 8])

Added this answer because the fromRange option wasn't mentioned yet.

回答4:

Swift 4.2

From existing array:

let arr = [1, 3, 8]
let indexSet = IndexSet(arr)

From array literal:

let indexSet: IndexSet = [1, 3, 8]

回答5:

You can use a NSMutableIndexSet and its addIndex method:

let array : [Int] = [1,2,3,4,5,7,8,10]
print(array)
let indexSet = NSMutableIndexSet()
for index in array {
    indexSet.addIndex(index)
}
print(indexSet)