如何获取在UITextView中键入的最后n个字符？

Question

Say I want to check if the last 5 characters typed in a UITextView are "mouse". How would I go about doing this? Specifically in Swift because of how strings indexes are different from Objective-C due to how emojis and the like are stored.

I cannot seem to figure this out. And keep in mind the last n characters may not be typed at the end of the text view, the cursor could be in the middle of the text.

Answer 1

您可以使用substringFromIndex与textView.text 。因此最后5个字符可以通过该代码来获得。

let strLast5: String =  textView.text.substringToIndex(countElements(textView.text) - 5);

Answer 2

This function will return the last n characters from the last cursor position in the textView, unless the cursor position is too close to the start of the string, in which case it will return from the start of the string to the cursor.

To check on each change make the ViewController a delegate of UITextViewDelegate and implement textViewDidChange()

class ViewController: UIViewController, UITextViewDelegate {

    override func viewDidLoad() {
        super.viewDidLoad()
        textView.delegate = self
    }

    func textViewDidChange(textView: UITextView) {
        print(lastNChars(5, textView: textView)!)
    }

    func lastNChars(n: Int, textView: UITextView) -> String? {
        if let selectedRange = textView.selectedTextRange {
            let startPosition: UITextPosition = textView.beginningOfDocument
            let cursorPosition = textView.offsetFromPosition(startPosition, toPosition: selectedRange.start)
            let chars = textView.text as String
            var lastNChars: Int!
            if n > cursorPosition {
                lastNChars = cursorPosition
            } else {
                lastNChars = n
            }
            let startOfIndex = chars.startIndex.advancedBy(cursorPosition - lastNChars)
            let endOfIndex = chars.startIndex.advancedBy(cursorPosition)
            let lastChars = chars.substringWithRange(startOfIndex ..< endOfIndex)
            return lastChars
        }
        return nil
    }
}

Answer 3

很快，您只需使用textView.text.last