ios - 如何获取 UITextView 中光标之前的字符？

Question

假设我有以下 UITextView 对象:

var textView = UITextView()
textView.text = "Hello World!"

现在假设我不想让用户在编辑时删除“W”字符。我怎么知道哪个字符在光标之前(或被光标选中)？

我正在寻找可以像这样工作的东西:

if textView.characterBeforeCursor() != "W" {
   textView.deleteBackward()
}

或者...(当用户选择“W”字符时):

if textView.selectedTextContains("W") == false {
   textView.deleteBackward()
}

我应该使用什么方法来实现这个目标？

Answer 1

这是一个想法，没有经过全面测试，但似乎可行...只需捕获要操作的角色并阻止退格键(如果它是目标)...还有关于文本选择，如果选择包含完全没有目标，我们阻止新文本。

import UIKit

class ViewController: UIViewController, UITextViewDelegate {

    @IBOutlet weak var textView: UITextView!

    override func viewDidLoad() {
        super.viewDidLoad()
        self.textView.delegate = self
        // Do any additional setup after loading the view, typically from a nib.
    }

    func characterBeforeCursor() -> String? {
        // get the cursor position
        if let cursorRange = textView.selectedTextRange {
            // get the position one character before the cursor start position
            if let newPosition = textView.position(from: cursorRange.start, offset: -1) {
                let range = textView.textRange(from: newPosition, to: cursorRange.start)
                return textView.text(in: range!)
            }
        }
        return nil
    }

    func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
        if (characterBeforeCursor() == "W") {
            let char = text.cString(using: String.Encoding.utf8)!
            let isBackSpace = strcmp(char, "\\b")
            if (isBackSpace == -92) {
                return false
            }
            return true
        }
        else {
            if let range = textView.selectedTextRange {
                let selectedText = textView.text(in: range)
                if (selectedText!.contains("W")) {
                    return false
                }
            }
            return true
        }
    }
}