warning: 'characters' is deprecated: Please use String or Substring directly

问题

characters - an instance property of String, is deprecated from with Xcode 9.1

It was very useful to get a substring from String by using the characters property but now it has been deprecated and Xcode suggests to use substring. I've tried to check around SO questions and apple developer tutorials/guidelines for the same. But could not see any solution/alternate as suggested.

Here is warning message:

'characters' is deprecated: Please use String or Substring

I've so many string operations are performed/handled using property characters.

Anyone have any idea/info about this update?

回答1:

Swift 4 introduced changes on string API.
You can just use !stringValue.isEmpty instead of stringValue.characters.count > 0

for more information you get the sample from here

for e.g

let edit = "Summary"
edit.count   // 7

回答2:

Swift 4 vs Swift 3 examples:

let myString = "test"

for char in myString.characters {print(char) } // Swift 3
for char in myString { print(char) } // Swift 4

let length = myString.characters.count // Swift 3
let length = myString.count // Swift 4

回答3:

One of the most common cases for manipulating strings is with JSON responses. In this example I created an extension in my watch app to drop the last (n) characters of a Bitcoin JSON object.

Swift 3:

func dropLast(_ n: Int = 0) -> String {
    return String(characters.dropLast(n))

Xcode 9.1 Error Message:

'characters' is deprecated: Please use String or Substring directly

Xcode is telling us to use the string variable or method directly.

Swift 4:

func dropLast(_ n: Int = 0) -> String {
    return String(dropLast(n))
    }

Complete Extension:

extension String {
    func dropLast(_ n: Int = 0) -> String {
        return String(dropLast(n))
    }

    var dropLast: String {
        return dropLast()
    }
}

Call:

print("rate:\(response.USDRate)")
let literalMarketPrice = response.USDRate.dropLast(2)
print("literal market price: \(literalMarketPrice)")

Console:

//rate:7,101.0888 //JSON float
//literal market price: 7,101.08 // JSON string literal

Additional Examples:

print("Spell has \(invisibleSpellName.count) characters.")
return String(dropLast(n))
return String(removeLast(n))

Documentation:

You'll often be using common methods such as dropLast() or removeLast() or count so here is the explicit Apple documentation for each method.

droplast()

removelast()

counting characters

回答4:

That warning is just a top of the iceberg, there were a loot of string changes, strings are again a collection of characters, but we got soemthing new and cool, subStrings :)

This is a great read about this: https://useyourloaf.com/blog/updating-strings-for-swift-4/

回答5:

Use this characters because String stopped being a collection in Swift 2.0. However this is still valid code in Swift 4 but is no longer necessary now that String is a Collection again.

For example a Swift 4 String now has a direct count property that gives the character count:

// Swift 4
let spString = "Stack"
spString.count           // 5

Examples for String and SubString.

String

Swift 4 String now directly get Element that gives the first character of String: ~~(string.characters.first)~~

let spString = "Stack"
let firstElement = spString.first   //S

SubString

Using SubString get first character.

let spstring = "Welcome"
let indexStartOfText = spstring.index(spstring.startIndex, offsetBy: 1)
let sub = spstring.substring(to: indexStartOfText)
print(sub) //W

回答6:

You can also use this code for dictionary grouping without using { $0.characters.first! }.

let cities = ["Shanghai": 24_256_800, "Karachi": 23_500_000, "Beijing": 21_516_000, "Seoul": 9_995_000]
let groupedCities = Dictionary(grouping: cities.keys) { $0.first! }
print(groupedCities)

来源：https://stackoverflow.com/questions/46467284/warning-characters-is-deprecated-please-use-string-or-substring-directly

标签

ios

string

substring

swift4

xcode9.1