1.从文件中读取内容

if let startWordsPath = Bundle.main.path(forResource: "start", ofType: "txt") {
        if let startWords = try? String(contentsOfFile: startWordsPath) {
             allWords = startWords.components(separatedBy: "\n")
        }

2.UITextChecker()类可以用来检查拼写的错误

func isReal(word: String) -> Bool {
    let checker = UITextChecker()
    let range = NSMakeRange(0, word.utf16.count)
    //返回第一处拼写错误的range
    let misspelledRange = checker.rangeOfMisspelledWord(in: word, range: range, startingAt: 0, wrap: false, language: "en")
    return misspelledRange.location == NSNotFound
}

3.unowned 和 weak

let submitAction = UIAlertAction(title: "Submit", style: .default) { [unowned self, ac] action in
    let answer = ac.textFields![0]
    self.submit(answer: answer.text!)
}

两者都是为了避免循环引用，区别是weak允许值为nil，而unowned不允许值为nil。