Struct属性关闭仅在Swift中运行一次

Question

Have any idea to let closure just run once.

Every time I call the APIResult . the property which is priceSortedItems will print "123". I want make it run once to reduce memory usage. Thanks.

struct APIResult {

    var aryItem = [Item]()

    var priceSortedItems: [Item] {

        print("123")

        let sortedItems = self.aryItem.sorted(by: { (item1, item2) -> Bool in
            Double(item1.Value)! > Double(item2.Value)!
        })

        return sortedItems
    }
}

Answer 1

Your property is counted property with getter . That means every time you need to get your variable, code inside getter gets executed and you get new value from getter .

If you want to initialize your variable just once, use lazy variable which gets initialized once when is needed:

lazy var priceSortedItems: [Item] = {

    print("123")

    let sortedItems = self.aryItem.sorted(by: { (item1, item2) -> Bool in
        Double(item1.Value)! > Double(item2.Value)!
    })

    return sortedItems
}()

Answer 2

If you want to update priceSortedItems once aryItem changed. You should do like this.

struct APIResult {

    var aryItem = [Item]() {
        didSet {
            priceSortedItems = aryItem.sorted(by: { (item1, item2) -> Bool in
                Double(item1.Value)! > Double(item2.Value)!
            })
        }
    }

    var priceSortedItems = [Item]()
}

Answer 3

func priceSortedItems() ->[Item] {

    print("123")

    let sortedItems = self.aryItem.sorted(by: { (item1, item2) -> Bool in
        Double(item1.Value)! > Double(item2.Value)!
    })

    return sortedItems
}

You can create it as a function.