在swift 2.0中

var stringMe="Something In this.World"
var needle="."
if let idx = stringMe.characters.indexOf(needle) {
    let pos=stringMe.substringFromIndex(idx)
    print("Found \(needle) at position \(pos)")
}
else {
    print("Not found")
}

你可以用这个找到字符串中一个字符的索引号:

var str = "abcdefghi"
if let index = str.firstIndex(of: "c") {
    let distance = str.distance(from: str.startIndex, to: index)
    // distance is 2
}

如果你想使用熟悉的NSString，你可以显式地声明它:

var someString: NSString = "abcdefghi"

var someRange: NSRange = someString.rangeOfString("c")

我还不确定如何在Swift中做到这一点。

    // Using Swift 4, the code below works.
    // The problem is that String.index is a struct. Use dot notation to grab the integer part of it that you want: ".encodedOffset"
    let strx = "0123456789ABCDEF"
    let si = strx.index(of: "A")
    let i = si?.encodedOffset       // i will be an Int. You need "?" because it might be nil, no such character found.

    if i != nil {                   // You MUST deal with the optional, unwrap it only if not nil.
        print("i = ",i)
        print("i = ",i!)            // "!" str1ps off "optional" specification (unwraps i).
            // or
        let ii = i!
        print("ii = ",ii)

    }
    // Good luck.

Swift 3.0让这个更加冗长:

let string = "Hello.World"
let needle: Character = "."
if let idx = string.characters.index(of: needle) {
    let pos = string.characters.distance(from: string.startIndex, to: idx)
    print("Found \(needle) at position \(pos)")
}
else {
    print("Not found")
}

扩展:

extension String {
    public func index(of char: Character) -> Int? {
        if let idx = characters.index(of: char) {
            return characters.distance(from: startIndex, to: idx)
        }
        return nil
    }
}

在Swift 2.0中，这变得更加容易:

let string = "Hello.World"
let needle: Character = "."
if let idx = string.characters.indexOf(needle) {
    let pos = string.startIndex.distanceTo(idx)
    print("Found \(needle) at position \(pos)")
}
else {
    print("Not found")
}

扩展:

extension String {
    public func indexOfCharacter(char: Character) -> Int? {
        if let idx = self.characters.indexOf(char) {
            return self.startIndex.distanceTo(idx)
        }
        return nil
    }
}

斯威夫特1。x实现:

对于纯Swift解决方案，可以使用:

let string = "Hello.World"
let needle: Character = "."
if let idx = find(string, needle) {
    let pos = distance(string.startIndex, idx)
    println("Found \(needle) at position \(pos)")
}
else {
    println("Not found")
}

作为String的扩展:

extension String {
    public func indexOfCharacter(char: Character) -> Int? {
        if let idx = find(self, char) {
            return distance(self.startIndex, idx)
        }
        return nil
    }
}

下面是一个干净的String扩展，回答了这个问题:

斯威夫特3:

extension String {
    var length:Int {
        return self.characters.count
    }

    func indexOf(target: String) -> Int? {

        let range = (self as NSString).range(of: target)

        guard range.toRange() != nil else {
            return nil
        }

        return range.location

    }
    func lastIndexOf(target: String) -> Int? {



        let range = (self as NSString).range(of: target, options: NSString.CompareOptions.backwards)

        guard range.toRange() != nil else {
            return nil
        }

        return self.length - range.location - 1

    }
    func contains(s: String) -> Bool {
        return (self.range(of: s) != nil) ? true : false
    }
}

斯威夫特2.2:

extension String {    
    var length:Int {
        return self.characters.count
    }

    func indexOf(target: String) -> Int? {

        let range = (self as NSString).rangeOfString(target)

        guard range.toRange() != nil else {
            return nil
        }

        return range.location

    }
    func lastIndexOf(target: String) -> Int? {



        let range = (self as NSString).rangeOfString(target, options: NSStringCompareOptions.BackwardsSearch)

        guard range.toRange() != nil else {
            return nil
        }

        return self.length - range.location - 1

    }
    func contains(s: String) -> Bool {
        return (self.rangeOfString(s) != nil) ? true : false
    }
}