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
}

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")
}

与Objective-C中的NSString相比，Swift中的变量类型String包含不同的函数。Sulthan提到过，

Swift String没有实现RandomAccessIndex

你能做的是向下转换你的变量类型String到NSString(这是有效的Swift)。这将给你访问NSString中的函数。

var str = "abcdefghi" as NSString
str.rangeOfString("c").locationx   // returns 2

extension String{
    func contains(find: String)->Bool{
        return self.range(of: find) != nil
    }
}
 
func check(n:String, h:String)->Int{
    let n1 = n.lowercased()
    let h1 = h.lowercased()//lowercase to make string case insensitive
    var pos = 0 //postion of substring
    if h1.contains(n1){
       // checking if sub string exists
        if let idx = h1.firstIndex(of:n1.first!){
             let pos1 = h1.distance(from: h1.startIndex, to: idx)
           pos = pos1
        }
        return pos
    }
    else{
        return -1
    }
}
 
print(check(n:"@", h:"hithisispushker,he is 99 a good Boy"))//put substring in n: and string in h

仔细想想，你其实并不需要位置的确切Int版本。范围甚至是字符串。如果需要，Index足以再次获取子字符串:

let myString = "hello"

let rangeOfE = myString.rangeOfString("e")

if let rangeOfE = rangeOfE {
    myString.substringWithRange(rangeOfE) // e
    myString[rangeOfE] // e

    // if you do want to create your own range
    // you can keep the index as a String.Index type
    let index = rangeOfE.startIndex
    myString.substringWithRange(Range<String.Index>(start: index, end: advance(index, 1))) // e

    // if you really really need the 
    // Int version of the index:
    let numericIndex = distance(index, advance(index, 1)) // 1 (type Int)
}

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
    }
}