let mystring:String = "indeep";
let findCharacter:Character = "d";

if (mystring.characters.contains(findCharacter))
{
    let position = mystring.characters.indexOf(findCharacter);
    NSLog("Position of c is \(mystring.startIndex.distanceTo(position!))")

}
else
{
    NSLog("Position of c is not found");
}

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
    }
}

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

在思考方面，这可能被称为反转。你会发现世界是圆的而不是平的。“你真的不需要知道角色的索引来处理它。”作为一名C程序员，我发现这也很难接受! 你的行“let index = letters.characters.indexOf("c")!”本身就足够了。 例如，要去掉c，你可以用…(操场粘贴)

    var letters = "abcdefg"
  //let index = letters.rangeOfString("c")!.startIndex //is the same as
    let index = letters.characters.indexOf("c")!
    range = letters.characters.indexOf("c")!...letters.characters.indexOf("c")!
    letters.removeRange(range)
    letters

然而，如果你想要一个索引，你需要返回一个实际的index而不是Int值，因为Int值对于任何实际使用都需要额外的步骤。这些扩展返回一个索引，一个特定字符的计数，以及这个游乐场插件代码将演示的范围。

extension String
{
    public func firstIndexOfCharacter(aCharacter: Character) -> String.CharacterView.Index? {

        for index in self.characters.indices {
            if self[index] == aCharacter {
                return index
            }

        }
        return nil
    }

    public func returnCountOfThisCharacterInString(aCharacter: Character) -> Int? {

        var count = 0
        for letters in self.characters{

            if aCharacter == letters{

                count++
            }
        }
        return count
    }


    public func rangeToCharacterFromStart(aCharacter: Character) -> Range<Index>? {

        for index in self.characters.indices {
            if self[index] == aCharacter {
                let range = self.startIndex...index
                return range
            }

        }
        return nil
    }

}



var MyLittleString = "MyVery:important String"

var theIndex = MyLittleString.firstIndexOfCharacter(":")

var countOfColons = MyLittleString.returnCountOfThisCharacterInString(":")

var theCharacterAtIndex:Character = MyLittleString[theIndex!]

var theRange = MyLittleString.rangeToCharacterFromStart(":")
MyLittleString.removeRange(theRange!)

斯威夫特3

extension String {
        func substring(from:String) -> String
        {
            let searchingString = from
            let rangeOfSearchingString = self.range(of: searchingString)!
            let indexOfSearchingString: Int = self.distance(from: self.startIndex, to: rangeOfSearchingString.upperBound )
            let trimmedString = self.substring(start: indexOfSearchingString , end: self.count)
            
            return trimmedString
        }
        
    }

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
    }
}