Ios 删除字符串开头的非字母字符

我想替换字符串中第一个字母之前的所有非字母数字字符（包括空格）

"\r\n                A Simple PDF File \r\n                   This is a small demonstration .pdf file - \r\n                   just for use in the Virtual Mechanics tutorials. More text. And more \r\n                   text."

我曾经

 let string = txtView.text
 let newString = string.replacingOccurrences(of: "\n", with: "")

---

但它将替换字符串的所有“\n”。如何仅替换起始字符？

您可以使用字符串类的

trimmingCharacters

方法。它将从字符串中删除所有前导和尾随空格和\n

let str = "\r\n                A Simple PDF File \r\n                   This is a small demonstration .pdf file - \r\n                   just for use in the Virtual Mechanics tutorials. More text. And more \r\n                   text."

let result = str.trimmingCharacters(in: .whitespacesAndNewlines)
print(result)

仅前导空格：

extension String {
    func removingLeadingSpaces() -> String {
        guard let index = firstIndex(where: { !CharacterSet(charactersIn: String($0)).isSubset(of: .whitespaces) }) else {
            return self
        }
        return String(self[index...])
    }
}

---

我能够使用正则表达式删除前导空格。代码如下：

extension String {
    func trimLeadingWhitespaces() -> String {
        return self.replacingOccurrences(of: "^\\s+", with: "", options: .regularExpression)
    }
}

let string = "       Some string     abc"
let trimmed = string.trimLeadingWhitespaces()
print(trimmed)

---

您可以从

extension

（thx@amer）使用两个

func

：

并使用它：

let myString = "\r\n                A Simple PDF File \r\n                   This is a small demonstration .pdf file - \r\n                   just for use in the Virtual Mechanics tutorials. More text. And more \r\n                   text."


let charactersRemoved = myString.replacingFirstOccurrence(of: "\r\n", with: "")
let whiteSpacesRemoved = charactersRemoved.removingLeadingSpaces()
print(whiteSpacesRemoved) // "A Simple PDF File \r\n                   This is a small demonstration .pdf file - \r\n                   just for use in the Virtual Mechanics tutorials. More text. And more \r\n                   text."

---

[|\t |\n |\r]

匹配空格、换行符、制表符或回车符

{2，}

“2次或更多”

每个匹配项都替换为换行符

let str=“\r\n一个简单的PDF文件\r\n这是一个小型演示.PDF文件-\r\n仅用于虚拟力学教程。更多文本。更多\r\n文本。”
让newString=str.replacingOccurrences(
其中：“[|\t |\n |\r]{2，}”，
加上“\n”，
选项：。正则表达式
)
印刷品（新闻字符串）
//一个简单的PDF文件
//这是一个小的演示.pdf文件-
//仅供在虚拟力学教程中使用。更多文本。还有更多
//文本。

根据您的问题陈述，您需要删除非字母字符，其中包括

空格、行“@”、“$”、“%”、“^”

等。有很多非字母字符。您可以单独验证字母字符，而不是检查非字母字符。请检查以下问题的解决方案

extension String{
    func findFirstAlphabetic() -> String.Index?{
        for index  in self.indices{
            if String(self[index]).isAlphanumeric == true{
                return index
            }
        }
        return nil
    }
    var isAlphanumeric: Bool {
        return !isEmpty && range(of: "[^a-zA-Z0-9]", options: .regularExpression) == nil
    }
    func alphabetic_Leading_SubString() -> String?{
        if let startIndex =  self.findFirstAlphabetic(){
            let newSubString = self[startIndex..<self.endIndex]
            return String(newSubString)
        }
        return nil
    }
}

输入：-

let string = "\r\n@ # $ % & ^ * () -+ #####@@@                A Simple PDF File \r\n                   This is a small demonstration .pdf file - \r\n                   just for use in the Virtual Mechanics tutorials. More text. And more \r\n                   text."

输出：-

---

有一个函数

drop

，在填充条件时删除字符

下面是使用它的两种变体

let newString = string.drop { $0.isWhitespace || $0.isPunctuation }
let newString = string.drop { !($0.isLetter || $0.isNumber) }

---

我不需要删除尾随空格、中间空格或新行来删除前导spaces@AwaisMobeen添加您期望的输出。您可以通过引用形成您自己的正则表达式：从字面上理解问题正则表达式相当于

“^[^[：alnum:][+”

@Awais Mobeen

请检查此项以解决您的问题您可以使用尾随闭包语法

删除{…}

注意，isLetter不包含数字您可以使用字符属性

isWhitespace

let string = "\r\n@ # $ % & ^ * () -+ #####@@@                A Simple PDF File \r\n                   This is a small demonstration .pdf file - \r\n                   just for use in the Virtual Mechanics tutorials. More text. And more \r\n                   text."

let newString = string.drop { $0.isWhitespace || $0.isPunctuation }
let newString = string.drop { !($0.isLetter || $0.isNumber) }