Swift：子字符串的简单方法？答案

【问题标题】：Swift: easy way to substring?Swift：子字符串的简单方法？
【发布时间】：2015-11-18 10:41:11
【问题描述】：

我有一个字符串：

myString = "mystring"

我只想获取前 5 个字符

在 Swift 中最简单的方法是什么？

【问题讨论】：

可能重复stackoverflow.com/questions/24044851/…

标签： swift substring

【解决方案1】：

let substring: String = (myString as NSString).substringToIndex(5)

【讨论】：

【解决方案2】：

Choppin 的正确答案，但如果你想以纯粹的快速方式（不强制转换为 NS String ：

 myString = myString.substringToIndex(advance(myString.startIndex, 5))

【讨论】：

这在 Swift 中是多么不直观，这太疯狂了
是的，我必须在每个项目中一次又一次地用谷歌搜索，因为我一直忘记它
这可能看起来很奇怪，但有充分的理由。例如stackoverflow.com/questions/24880604/…
伟大的加法阿比伦！
在 Swift 3 中不再工作，但这里有一个工作扩展：stackoverflow.com/questions/24044851/…

【解决方案3】：

使用这些扩展：

斯威夫特 2.3

extension String
{
    func substringFromIndex(index: Int) -> String
    {
        if (index < 0 || index > self.characters.count)
        {
            print("index \(index) out of bounds")
            return ""
        }
        return self.substringFromIndex(self.startIndex.advancedBy(index))
    }

    func substringToIndex(index: Int) -> String
    {
        if (index < 0 || index > self.characters.count)
        {
            print("index \(index) out of bounds")
            return ""
        }
        return self.substringToIndex(self.startIndex.advancedBy(index))
    }

    func substringWithRange(start: Int, end: Int) -> String
    {
        if (start < 0 || start > self.characters.count)
        {
            print("start index \(start) out of bounds")
            return ""
        }
        else if end < 0 || end > self.characters.count
        {
            print("end index \(end) out of bounds")
            return ""
        }
        let range = Range(start: self.startIndex.advancedBy(start), end: self.startIndex.advancedBy(end))
        return self.substringWithRange(range)
    }

    func substringWithRange(start: Int, location: Int) -> String
    {
        if (start < 0 || start > self.characters.count)
        {
            print("start index \(start) out of bounds")
            return ""
        }
        else if location < 0 || start + location > self.characters.count
        {
            print("end index \(start + location) out of bounds")
            return ""
        }
        let range = Range(start: self.startIndex.advancedBy(start), end: self.startIndex.advancedBy(start + location))
        return self.substringWithRange(range)
    }
}

斯威夫特 3

extension String
{   
    func substring(from index: Int) -> String
    {
        if (index < 0 || index > self.characters.count)
        {
            print("index \(index) out of bounds")
            return ""
        }
        return self.substring(from: self.characters.index(self.startIndex, offsetBy: index))
    }

    func substring(to index: Int) -> String
    {
        if (index < 0 || index > self.characters.count)
        {
            print("index \(index) out of bounds")
            return ""
        }
        return self.substring(to: self.characters.index(self.startIndex, offsetBy: index))
    }

    func substring(start: Int, end: Int) -> String
    {
        if (start < 0 || start > self.characters.count)
        {
            print("start index \(start) out of bounds")
            return ""
        }
        else if end < 0 || end > self.characters.count
        {
            print("end index \(end) out of bounds")
            return ""
        }
        let startIndex = self.characters.index(self.startIndex, offsetBy: start)
        let endIndex = self.characters.index(self.startIndex, offsetBy: end)
        let range = startIndex..<endIndex

        return self.substring(with: range)
    }

    func substring(start: Int, location: Int) -> String
    {
        if (start < 0 || start > self.characters.count)
        {
            print("start index \(start) out of bounds")
            return ""
        }
        else if location < 0 || start + location > self.characters.count
        {
            print("end index \(start + location) out of bounds")
            return ""
        }
        let startIndex = self.characters.index(self.startIndex, offsetBy: start)
        let endIndex = self.characters.index(self.startIndex, offsetBy: start + location)
        let range = startIndex..<endIndex

        return self.substring(with: range)
    }
}

用法：

let myString = "mystring"
let substring = myString.substringToIndex(5)

【讨论】：