在Swift中设置UITextField的最大字符长度

更新Fattie的回答：

extension UITextField {

    // Runtime key
    private struct AssociatedKeys {
        // Maximum length key
        static var maxlength: UInt8 = 0
        // Temporary string key
        static var tempString: UInt8 = 0
    }

    // Limit the maximum input length of the textfiled
    @IBInspectable var maxLength: Int {
        get {
            return objc_getAssociatedObject(self, &AssociatedKeys.maxlength) as? Int ?? 0
        }
        set {
            objc_setAssociatedObject(self, &AssociatedKeys.maxlength, newValue, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN_NONATOMIC)
            addTarget(self, action: #selector(handleEditingChanged(textField:)), for: .editingChanged)
        }
    }

    // Temporary string
    private var tempString: String? {
        get {
            return objc_getAssociatedObject(self, &AssociatedKeys.tempString) as? String
        }
        set {
            objc_setAssociatedObject(self, &AssociatedKeys.tempString, newValue, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN_NONATOMIC)
        }
    }

    // When the text changes, process the amount of text in the input
    // box so that its length is within the controllable range.
    @objc private func handleEditingChanged(textField: UITextField) {

        // Special processing for the Chinese input method
        guard markedTextRange == nil else { return }

        if textField.text?.count == maxLength {

            // Set lastQualifiedString where text length == maximum length
            tempString = textField.text
        } else if textField.text?.count ?? 0 < maxLength {

            // Clear lastQualifiedString when text length > maxlength
            tempString = nil
        }

        // Keep the current text range in arcgives
        let archivesEditRange: UITextRange?

        if textField.text?.count ?? 0 > maxLength {

            // If text length > maximum length, remove last range and to move to -1 postion.
            let position = textField.position(from: safeTextPosition(selectedTextRange?.start), offset: -1) ?? textField.endOfDocument
            archivesEditRange = textField.textRange(from: safeTextPosition(position), to: safeTextPosition(position))
        } else {

            // Just set current select text range
            archivesEditRange = selectedTextRange
        }

        // Main handle string maximum length
        textField.text = tempString ?? String((textField.text ?? "").prefix(maxLength))

        // Last configuration edit text range
        textField.selectedTextRange = archivesEditRange
    }

    // Get safe textPosition
    private func safeTextPosition(_ optionlTextPosition: UITextPosition?) -> UITextPosition {

        /* beginningOfDocument -> The end of the the text document. */
        return optionlTextPosition ?? endOfDocument
    }
}

只需检查字符串中的字符数即可。

1. Add a delegate to view controller and assign the delegate

   class YorsClassName : UITextFieldDelegate {
   
   }
   

2. Check the number of characters allowed for the text field

   func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
       if textField.text?.count == 1 {
           return false
       }
       return true
   }
   

注意：这里我只检查了textField中允许的字符。

我需要补充一下Alaeddine的答案：

1. Your view controller should conform to UITextFieldDelegate

    class MyViewController: UIViewController, UITextViewDelegate {
   
    }
   

2. Set the delegate of your textfield:

   To set the delegate, you can control drag from the textfield to your view controller in the storyboard. I think this is preferable to setting it in code

3. Implement the method in your view controller:

    textField(_:shouldChangeCharactersInRange:replacementString:)
   

1. Set the delegate of your textfield:

    textField.delegate = self
   

2. Implement the method in your view controller:

    // MARK: Text field delegate
   
    extension ViewController: UITextFieldDelegate {
        func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
            return range.location < maxLength (maxLength can be any maximum length you can define)
        }
    }
   

Swift 4中阻止文本后限制字符的文本框

func textField(_ textField: UITextField, shouldChangeCharactersIn range: 
    NSRange,replacementString string: String) -> Bool
{


    if textField == self.txtDescription {
        let maxLength = 200
        let currentString: NSString = textField.text! as NSString
        let newString: NSString = currentString.replacingCharacters(in: range, with: string) as NSString
        return newString.length <= maxLength
    }

    return true


}

这个答案适用于Swift 4，非常简单，可以让退格键通过。

func textField(_ textField: UITextField,
               shouldChangeCharactersIn range: NSRange,
               replacementString string: String) -> Bool {
    return textField.text!.count < 10 || string == ""
}

这在Swift 4中有效

步骤1：设置UITextFieldDelegate

class SignUPViewController: UIViewController , UITextFieldDelegate {

   @IBOutlet weak var userMobileNoTextFiled: UITextField!

    override func viewDidLoad() {
        super.viewDidLoad()

步骤二：设置代理

        userMobileNoTextFiled.delegate = self                  // Set delegate
   }

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    //        guard let text = userMobileNoTextFiled.text else { return true }
    //        let newLength = text.count + string.count - range.length
    //        return newLength <= 10
    //    }

步骤三：调用函数

    func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
        let maxLength = 10          // Set your need
        let currentString: NSString = textField.text! as NSString
        let newString: NSString =
            currentString.replacingCharacters(in: range, with: string) as NSString
        return newString.length <= maxLength
    }
}

我使用以下步骤。首先在viewdidload中设置委托文本字段。

override func viewDidLoad() {
    super.viewDidLoad()

    textfield.delegate = self
}

在包含UITextFieldDelegate之后，您应该使用shouldChangeCharactersIn函数。

extension viewController: UITextFieldDelegate {
    func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
        let newLength = (textField.text?.utf16.count)! + string.utf16.count - range.length
        if newLength <= 8 {
            return true
        }
        else {
            return false
        }
    }
}

这里提供了一种Swift 3.2+的替代方案，避免了不必要的字符串操作。在本例中，最大长度为10：

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    let text = textField.text ?? ""

    return text.count - range.length + string.count <= 10
}

为了避免出现问题，请在将范围大小应用于字符串之前确保对其进行保护。否则，如果用户执行以下操作，您将会遇到崩溃：

• 输入最大长度文本
• 插入某些内容（由于长度限制，不会插入任何内容，但iOS并不知道这一点）
• 撤消插入操作（您将遇到崩溃，因为范围将超过实际字符串大小）

此外，使用iOS 13，用户可能会意外触发此问题。

我建议您将此添加到您的项目中：

extension String {
    func replace(with text: String, in range: NSRange) -> String? {
        // NOTE: NSString conversion is necessary to operate in the same symbol steps
        // Otherwise, you may not be able to delete an emoji, for example
        let current = NSString(string: self)
        guard range.location + range.length <= current.length else { return nil }
        return current.replacingCharacters(in: range, with: text)
    }
}

并像这样使用：

func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
    guard let newText = textView.text.replace(with: text, in: range) else { return false }
    return newText.count < maxNumberOfCharacters
    // NOTE: You may wanna trim the new text instead,
    // so the user will able to shove his long text at least partially
}

否则，您的应用程序将经常崩溃。