如何在 Swift 中连接字符串？

Question

How to concatenate string in Swift?

In Objective-C we do like

NSString *string = @"Swift";
NSString *resultStr = [string stringByAppendingString:@" is a new Programming Language"];

or

NSString *resultStr=[NSString stringWithFormat:@"%@ is a new Programming Language",string];

But I want to do this in Swift-language.

Answer 1

You can concatenate strings a number of ways:

let a = "Hello"
let b = "World"

let first = a + ", " + b
let second = "\(a), \(b)"

You could also do:

var c = "Hello"
c += ", World"

I'm sure there are more ways too.

Bit of description

let creates a constant. (sort of like an NSString ). You can't change its value once you have set it. You can still add it to other things and create new variables though.

var creates a variable. (sort of like NSMutableString ) so you can change the value of it. But this has been answered several times on Stack Overflow, (see difference between let and var ).

Note

In reality let and var are very different from NSString and NSMutableString but it helps the analogy.

Answer 2

You can add a string in these ways:

• str += ""
• str = str + ""
• str = str + str2
• str = "" + ""
• str = "\\(variable)"
• str = str + "\\(variable)"

I think I named them all.

Answer 3

var language = "Swift" 
var resultStr = "\(language) is a new programming language"

Answer 4

This will work too:

var string = "swift"
var resultStr = string + " is a new Programming Language"

Answer 5

\\ this is being used to append one string to another string.

var first = "Hi" 
var combineStr = "\(first) Start develop app for swift"

You can try this also:- + keyword.

 var first = "Hi" 
 var combineStr = "+(first) Start develop app for swift"

Try this code.

Answer 6

let the_string = "Swift"
let resultString = "\(the_string) is a new Programming Language"

Answer 7

Very Simple:

let StringA = "Hello"
let StringB = "World"
let ResultString = "\(StringA)\(StringB)"
println("Concatenated result = \(ResultString)")

Answer 8

You can now use stringByAppendingString in Swift.

var string = "Swift"
var resultString = string.stringByAppendingString(" is new Programming Language")

Answer 9

Xcode didn't accept optional strings added with a normal string. I wrote this extensions to solve that problem:

extension String {
    mutating func addString(str: String) {
        self = self + str
    }
}

Then you can call it like:

var str1: String?
var str1 = "hi"
var str2 = " my name is"
str1.addString(str2)
println(str1) //hi my name is

However you could now also do something like this:

var str1: String?
var str1 = "hi"
var str2 = " my name is"
str1! += str2

Answer 10

It is called as String Interpolation. It is way of creating NEW string with CONSTANTS, VARIABLE, LITERALS and EXPRESSIONS. for examples:

      let price = 3
      let staringValue = "The price of \(price) mangoes is equal to \(price*price) "

also

let string1 = "anil"
let string2 = "gupta"
let fullName = string1 + string2  // fullName is equal to "anilgupta"
or 
let fullName = "\(string1)\(string2)" // fullName is equal to "anilgupta"

it also mean as concatenating string values.

Hope this helps you.

Answer 11

To print the combined string using

Println("\(string1)\(string2)")

or String3 stores the output of combination of 2 strings

let strin3 = "\(string1)\(string2)"

Answer 12

One can also use stringByAppendingFormat in Swift.

var finalString : NSString = NSString(string: "Hello")
finalString = finalString.stringByAppendingFormat("%@", " World")
print(finalString) //Output:- Hello World
finalString = finalString.stringByAppendingFormat("%@", " Of People")
print(finalString) //Output:- Hello World Of People

Answer 13

Swift 4.2

You can also use an extension:

extension Array where Element == String? {
    func compactConcate(separator: String) -> String {
        return self.compactMap { $0 }.filter { !$0.isEmpty }.joined(separator: separator)
    }
}

Use:

label.text = [m.firstName, m.lastName].compactConcate(separator: " ")

Result:

"The Man"
"The"
"Man"

Answer 14

From: Matt Neuburg Book “iOS 13 Programming Fundamentals with Swift.” :

To combine (concatenate) two strings, the simplest approach is to use the + operator :

let s = "hello"
let s2 = " world"
let greeting = s + s2

This convenient notation is possible because the + operator is overloaded: it does one thing when the operands are numbers (numeric addition) and another when the operands are strings (concatenation). The + operator comes with a += assignment shortcut; naturally, the variable on the left side must have been declared with var:

var s = "hello"
let s2 = " world"
s += s2

As an alternative to += , you can call the append(_:) instance method:

var s = "hello"
let s2 = " world"
s.append(s2)

Another way of concatenating strings is with the joined(separator:) method. You start with an array of strings to be concatenated, and hand it the string that is to be inserted between all of them:

let s = "hello"
let s2 = "world"
let space = " "
let greeting = [s,s2].joined(separator:space)

Answer 15

Swift 5

You can achieve it using appending API. This returns a new string made by appending a given string to the receiver.

API Details : here

Use :

var text = "Hello"
text = text.appending(" Namaste")

Result :

Hello
Hello Namaste

Answer 16

You could use SwiftString ( https://github.com/amayne/SwiftString ) to do this.

"".join(["string1", "string2", "string3"]) // "string1string2string"
" ".join(["hello", "world"]) // "hello world"

DISCLAIMER: I wrote this extension

Answer 17

刚从Objective-C切换到Swift（4），发现自己经常使用：

let allWords = String(format:"%@ %@ %@",message.body!, message.subject!, message.senderName!)

Answer 18

Several words about performance

UI Testing Bundle on iPhone 7(real device) with iOS 14

var result = ""
for i in 0...count {
    <concat_operation>
}

Count = 5_000

//Append
result.append(String(i))                         //0.007s 39.322kB

//Plus Equal
result += String(i)                              //0.006s 19.661kB

//Plus
result = result + String(i)                      //0.130s 36.045kB

//Interpolation
result = "\(result)\(i)"                         //0.164s 16.384kB

//NSString
result = NSString(format: "%@%i", result, i)     //0.354s 108.142kB

//NSMutableString
result.append(String(i))                         //0.008s 19.661kB

Disable next tests:

• Plus up to 100_000 ~10s
• interpolation up to 100_000 ~10s
• NSString up to 10_000 -> memory issues

Count = 1_000_000

//Append
result.append(String(i))                         //0.566s 5894.979kB

//Plus Equal
result += String(i)                              //0.570s 5894.979kB

//NSMutableString
result.append(String(i))                         //0.751s 5891.694kB

*Note about Convert Int to String

Source code

import XCTest

class StringTests: XCTestCase {

    let count = 1_000_000
    
    let metrics: [XCTMetric] = [
        XCTClockMetric(),
        XCTMemoryMetric()
    ]
    
    let measureOptions = XCTMeasureOptions.default

    
    override func setUp() {
        measureOptions.iterationCount = 5
    }
    
    func testAppend() {
        var result = ""
        measure(metrics: metrics, options: measureOptions) {
            for i in 0...count {
                result.append(String(i))
            }
        }

    }
    
    func testPlusEqual() {
        var result = ""
        measure(metrics: metrics, options: measureOptions) {
            for i in 0...count {
                result += String(i)
            }
        }
    }
    
    func testPlus() {
        var result = ""
        measure(metrics: metrics, options: measureOptions) {
            for i in 0...count {
                result = result + String(i)
            }
        }
    }
    
    func testInterpolation() {
        var result = ""
        measure(metrics: metrics, options: measureOptions) {
            for i in 0...count {
                result = "\(result)\(i)"
            }
        }
    }
    
    //Up to 10_000
    func testNSString() {
        var result: NSString =  ""
        measure(metrics: metrics, options: measureOptions) {
            for i in 0...count {
                result = NSString(format: "%@%i", result, i)
            }
        }
    }
    
    func testNSMutableString() {
        let result = NSMutableString()
        measure(metrics: metrics, options: measureOptions) {
            for i in 0...count {
                result.append(String(i))
            }
        }
    }

}

Answer 19

Concatenation refers to the combining of Strings in Swift. Strings may contain texts, integers, or even emojis! There are many ways to String Concatenation. Let me enumerate some:

Same String

Using +=

This is useful if we want to add to an already existing String. For this to work, our String should be mutable or can be modified, thus declaring it as a Variable. For instance:

var myClassmates = "John, Jane"
myClassmates += ", Mark" // add a new Classmate
// Result: "John, Jane, Mark"

Different Strings

If we want to combine different Strings together, for instance:

let oldClassmates = "John, Jane" 
let newClassmate = "Mark"

We can use any of the following:

1) Using +

let myClassmates = oldClassmates + ", " + newClassmate
// Result: "John, Jane, Mark"

Notice that the each String may be a Variable or a Constant. Declare it as a Constant if you're only gonna change the value once.

2) String Interpolation

let myClassmates = "\(oldClassmates), \(newClassmate)"
// Result: "John, Jane, Mark"

3) Appending

let myClassmates = oldClassmates.appending(newClassmate)
// Result: "John, Jane, Mark"

Refer to Strings & Characters from the Swift Book for more.

Update: Tested on Swift 5.1

Answer 20

In Swift 5 apple has introduces Raw Strings using # symbols.

Example:

print(#"My name is "XXX" and I'm "28"."#)
let name = "XXX"
print(#"My name is \#(name)."#)

symbol # is necessary after \\. A regular \\(name) will be interpreted as characters in the string.

Answer 21

Swift 5:

Array of strings into a single string

let array = ["Ramana", "Meharshi", "Awareness", "Oneness", "Enlightnment", "Nothing"]
let joined = array.joined(separator: ", ")