更新答案@Arsonik对Swift 2.2的回答，使用比其他提供的解决方案更少的冗长代码:

extension String {
    func isValidEmail() -> Bool {
        let regex = try? NSRegularExpression(pattern: "^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$", options: .CaseInsensitive)
        return regex?.firstMatchInString(self, options: [], range: NSMakeRange(0, self.characters.count)) != nil
    }
}

@JeffersonBe的答案是接近的，但如果字符串是“包含someone@something.com一个有效的电子邮件”，这不是我们想要的。下面是String上的一个扩展，它工作得很好(并且允许测试有效的phoneNumber和其他数据检测器来引导。

/// Helper for various data detector matches.
/// Returns `true` iff the `String` matches the data detector type for the complete string.
func matchesDataDetector(type: NSTextCheckingResult.CheckingType, scheme: String? = nil) -> Bool {
    let dataDetector = try? NSDataDetector(types: type.rawValue)
    guard let firstMatch = dataDetector?.firstMatch(in: self, options: NSRegularExpression.MatchingOptions.reportCompletion, range: NSRange(location: 0, length: length)) else {
        return false
    }
    return firstMatch.range.location != NSNotFound
        // make sure the entire string is an email, not just contains an email
        && firstMatch.range.location == 0
        && firstMatch.range.length == length
        // make sure the link type matches if link scheme
        && (type != .link || scheme == nil || firstMatch.url?.scheme == scheme)
}
/// `true` iff the `String` is an email address in the proper form.
var isEmail: Bool {
    return matchesDataDetector(type: .link, scheme: "mailto")
}
/// `true` iff the `String` is a phone number in the proper form.
var isPhoneNumber: Bool {
    return matchesDataDetector(type: .phoneNumber)
}
/// number of characters in the `String` (required for above).
var length: Int {
    return self.characters.count
}

我改进了@Azik的答案。我允许使用准则允许的更多特殊字符，并返回一些无效的额外边缘情况。

小组认为这里只允许本地部分的。_%+-是不正确的。参见@Anton Gogolev对这个问题的回答或参见下文:

The local-part of the email address may use any of these ASCII characters: uppercase and lowercase Latin letters A to Z and a to z; digits 0 to 9; special characters !#$%&'*+-/=?^_`{|}~; dot ., provided that it is not the first or last character unless quoted, and provided also that it does not appear consecutively unless quoted (e.g. John..Doe@example.com is not allowed but "John..Doe"@example.com is allowed); space and "(),:;<>@[\] characters are allowed with restrictions (they are only allowed inside a quoted string, as described in the paragraph below, and in addition, a backslash or double-quote must be preceded by a backslash); comments are allowed with parentheses at either end of the local-part; e.g. john.smith(comment)@example.com and (comment)john.smith@example.com are both equivalent to john.smith@example.com;

我使用的代码将不允许限制性的特殊字符，但将允许比这里的大多数答案更多的选项。我更喜欢更宽松的验证，而不是谨慎的错误。

if enteredText.contains("..") || enteredText.contains("@@") 
   || enteredText.hasPrefix(".") || enteredText.hasSuffix(".con"){
       return false
}

let emailFormat = "[A-Z0-9a-z.!#$%&'*+-/=?^_`{|}~]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,64}"
let emailPredicate = NSPredicate(format:"SELF MATCHES %@", emailFormat)     
return emailPredicate.evaluate(with: enteredText)

在Swift 5.7中，在Regex类的帮助下，我们可以以简单有效的方式验证电子邮件地址

private func isValidEmail(_ email: String) -> Bool {
      guard let emailRegex = try? Regex("[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,64}")  
      else { return false }
      return email.firstMatch(of: emailRegex) != nil
   }

我们还可以使用属性包装器来提高效率:

@propertyWrapper
struct EmailPropertyWrapper {
  private var _value: String
  var wrappedValue: String {
    get { return isValidEmail(_value) ? _value : String() }
    set { _value = newValue }
  }
  
  init(email: String) {
    _value = email
  }

  private func isValidEmail(_ email: String) -> Bool {
      guard let emailRegex = try? Regex("[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,64}")  
      else { return false }
      return email.firstMatch(of: emailRegex) != nil
   }
}

struct User {
  var name: String
  @EmailPropertyWrapper var email: String
  
  func validateProperty() -> Bool {
    if name.isEmpty || email.isEmpty { return false }
    return true
  }
}

let user = User(name: "Sy", email: .init(email: "wwdc@icloud.com"))

print(user.validateProperty())

这是@Fattie的“THE REASONABLE SOLUTION”的新版本，在Swift 4.1的一个名为String+Email.swift的新文件中测试:

import Foundation

extension String {
    private static let __firstpart = "[A-Z0-9a-z]([A-Z0-9a-z._%+-]{0,30}[A-Z0-9a-z])?"
    private static let __serverpart = "([A-Z0-9a-z]([A-Z0-9a-z-]{0,30}[A-Z0-9a-z])?\\.){1,5}"
    private static let __emailRegex = __firstpart + "@" + __serverpart + "[A-Za-z]{2,6}"

    public var isEmail: Bool {
        let predicate = NSPredicate(format: "SELF MATCHES %@", type(of:self).__emailRegex)
        return predicate.evaluate(with: self)
    }
}

所以它的用法很简单:

let str = "mail@domain.com"
if str.isEmail {
    print("\(str) is a valid e-mail address")
} else {
    print("\(str) is not a valid e-mail address")
}

我只是不喜欢向String对象添加func，因为作为电子邮件地址是它们固有的(或不是)。根据我的理解，Bool属性比func更适合。

如果你正在寻找一个干净简单的解决方案，你应该看看https://github.com/nsagora/validation-components。

它包含一个电子邮件验证谓词，很容易集成在你的代码:

let email = "test@example.com"
let rule = EmailValidationPredicate()
let isValidEmail = rule.evaluate(with: email)

在引擎盖后面，它使用RFC 5322 regex (http://emailregex.com):

let regex = "(?:[\\p{L}0-9!#$%\\&'*+/=?\\^_`{|}~-]+(?:\\.[\\p{L}0-9!#$%\\&'*+/=?\\^_`{|}" +
    "~-]+)*|\"(?:[\\x01-\\x08\\x0b\\x0c\\x0e-\\x1f\\x21\\x23-\\x5b\\x5d-\\" +
    "x7f]|\\\\[\\x01-\\x09\\x0b\\x0c\\x0e-\\x7f])*\")@(?:(?:[\\p{L}0-9](?:[a-" +
    "z0-9-]*[\\p{L}0-9])?\\.)+[\\p{L}0-9](?:[\\p{L}0-9-]*[\\p{L}0-9])?|\\[(?:(?:25[0-5" +
    "]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-" +
    "9][0-9]?|[\\p{L}0-9-]*[\\p{L}0-9]:(?:[\\x01-\\x08\\x0b\\x0c\\x0e-\\x1f\\x21" +
    "-\\x5a\\x53-\\x7f]|\\\\[\\x01-\\x09\\x0b\\x0c\\x0e-\\x7f])+)\\])"