Swift中String含有emoji表情,长度计算不准确；

Swift：
Sting没有length方法，获取字符串长度使用count；

OC:
NSString使用.length获取长度；

场景：在存在emoji的的字符串下，Swift和OC混编时候如果用count取，导致匹配长度不够；

• NSString是由UTF-16单元构成
• length方法返回的是基于UTF-16的长度
• Swift的count返回的只是Unicode字符个数

结论： Swift的utf16.count是对应NSString的.length方法

    private func allRangeOf(searchString: String, from: String) -> [NSRange] {
        let scanner = Scanner(string: from)
        scanner.caseSensitive = true
        scanner.charactersToBeSkipped = CharacterSet(charactersIn: "")
        scanner.scanLocation = 0
        var rangeArray: [NSRange] = []
        while !scanner.isAtEnd {
            if scanner.scanString(searchString, into: nil) {
                let location = scanner.scanLocation - searchString.length
                let range = NSRange(location: location, length: searchString.length)
                rangeArray.append(range)
            } else {
                scanner.scanLocation += 1
            }
        }
        return rangeArray
    }