UITextField在Swift中设置最大字符长度

问题描述

如何覆盖此UITextField函数，使其对最大字符数有所限制？

How can I override this UITextField function so that it will have a limit on the maximum number of characters?

override func shouldChangeText(in range: UITextRange, replacementText text: String) -> Bool {

}

我在堆栈上做了一些研究，但是我所能找到的就是这个功能（见下文）。首先，我看不到如何覆盖，其次，它使用NSRange作为我拥有UITextRange的参数。如何实现呢？谢谢

I've done some research on stack, but all I can find is this function (see below). First off, I can't see how this can be an override, and second, it's using NSRange as a parameter where I have UITextRange. How can this be implemented? thanks

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange,
                replacementString string: String) -> Bool {
        let currentString: NSString = textField.text! as NSString
        let newString: NSString = currentString.replacingCharacters(in: range, with: string) as NSString
        return newString.length <= 4
    }

我的尝试失败：

override func shouldChangeText(in range: UITextRange, replacementText text: String) -> Bool {
        let currentString: NSString = self.text! as NSString
        let newString: NSString = currentString.replacingCharacters(in: range, with: text) as NSString
        return newString.length <= 4
    }

错误：无法将类型 UITextRange的值转换为预期的参数类型 NSRange（又名 _NSRange）

error: Cannot convert value of type 'UITextRange' to expected argument type 'NSRange' (aka '_NSRange')

推荐答案

您可以将UITextField子类化，并为UIControlEvents editedChanged添加目标。在选择器方法内部，您可以使用集合方法前缀来限制添加到textfield文本属性中的字符，如下所示：

You can subclass UITextField and add a target for UIControlEvents editingChanged. Inside the selector method you can use collection method prefix to limit the characters added to your textfield text property as follow:

import UIKit
class LimitedLengthField: UITextField {
    var maxLength: Int = 10
    override func willMove(toSuperview newSuperview: UIView?) {
        addTarget(self, action: #selector(editingChanged), for: .editingChanged)
        editingChanged()
    }
    @objc func editingChanged() {
        text = String(text!.prefix(maxLength))
    }
}

---

您可以添加自定义文本字段以编程方式或使用界面生成器：

---

You can add your custom text field programatically or using the interface builder:

import UIKit

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        let limitedLenghtField = LimitedLengthField(frame: CGRect(origin: CGPoint(x: 50, y: 50), size: CGSize(width: 200, height: 50)))
        limitedLenghtField.text = "123456789012345"
        view.addSubview(limitedLenghtField)
    }
}

这篇关于UITextField在Swift中设置最大字符长度的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！