How can I iterate over all items in NSMapTable in Swift

Question

I'm trying something like this in Swift but not working. Error is: Type () does not conform to type BooleanType

//visibleCollectionReusableHeaderViews is of type NSMapTable!

var enumerator: NSEnumerator = visibleCollectionReusableHeaderViews.objectEnumerator()
var myValue: AnyObject!

while (( myValue = enumerator.nextObject()))
{

}

What am I doing wrong? I don't think I understand how to iterate over an NSMapTable, or even just to get the first item in it.

score 18 · Accepted Answer · answered Aug 25 '14 at 14:14

18

In Swift, this is done using conditional assignment.

let enumerator = visibleCollectionReusableHeaderViews.objectEnumerator()

while let myValue: AnyObject = enumerator.nextObject() {
    println(myValue)
}

Note the non optional type for myValue. Otherwise this loop would be infinite as myValue continued to accept nil objects.

answered Aug 25 '14 at 14:14

Mick MacCallum

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Thanks this did it! By any chance, know of any way to now update a section in a uicollectionview? myValue actually is my header reusable view UICollectionElementKindSectionHeader so i'd like to visually redraw the items in there (the manual constraints need a refresh). I can do uicollectionview.reloaddata() but it's a little slow and redraws the ENTIRE view when I just need the header. – NullHypothesis Aug 25 '14 at 14:18
@user3379785 Well, if you're okay with reloading the entire section, you could use `collectionView.reloadSections(NSIndexSet(index: someIndexInteger))`, but if you're only interested in reloading the header, then I'm not exactly sure. It does look like a few options are explored here though. http://stackoverflow.com/questions/13831035/reload-uicollectionview-header-or-footer – Mick MacCallum Aug 25 '14 at 14:23
3

You will need to put `enumator.nextObject() as? YourObject` if you want to use methods on YourObject, for example. – theblang Jun 01 '15 at 02:10

score 4 · Answer 2 · answered Jul 14 '17 at 08:25

4

Or a clearer and shorter approach (Swift 3):

for key in table.keyEnumerator() {
    print(key)
}

for object in table.objectEnumerator() ?? NSEnumerator() {
    print(object)
}

answered Jul 14 '17 at 08:25

Ian Bytchek

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How can I iterate over all items in NSMapTable in Swift

2 Answers2