Swift 3版本 //*****这将不工作与Swift 2.x!* * * * * / /

首先创建一个新的Swift文件:TextFieldMaxLength.swift， 然后添加下面的代码:

import UIKit

private var maxLengths = [UITextField: Int]()

extension UITextField {

   @IBInspectable var maxLength: Int {

      get {

          guard let length = maxLengths[self] 
             else {
                return Int.max
      }
      return length
   }
   set {
      maxLengths[self] = newValue
      addTarget(
         self,
         action: #selector(limitLength),
         for: UIControlEvents.editingChanged
      )
   }
}
func limitLength(textField: UITextField) {
    guard let prospectiveText = textField.text,
        prospectiveText.characters.count > maxLength
    else {
        return
    }

   let selection = selectedTextRange
   let maxCharIndex = prospectiveText.index(prospectiveText.startIndex, offsetBy: maxLength)
   text = prospectiveText.substring(to: maxCharIndex)
   selectedTextRange = selection
   }
}

然后你会看到在故事板一个新的字段(最大长度)当你选择任何TextField

如果你还有更多问题，请查看这个链接:http://www.globalnerdy.com/2016/05/18/ios-programming-trick-how-to-use-xcode-to-set-a-text-fields-maximum-length-visual-studio-style/

使用这段代码在这里RESTRICTED_LENGTH是长度你想限制的文本字段。

   - (BOOL)textField:(UITextField *)textField     shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
    if (textField == nameTF) {
    int limit = RESTRICTED_LENGTH - 1;
    return !([textField.text length]>limit && [string length] > range.length);
    }
   else
   {
    return YES;
   }

return NO;

}

这是处理UITextField最大长度的正确方法，它允许返回键退出辞职文本字段作为第一响应器，并让用户在达到限制时退格

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
int MAX_LENGHT = 5;
    if([string isEqualToString:@"\n"])
    {
        [textField resignFirstResponder];
        return FALSE;
    }
    else if(textField.text.length > MAX_LENGHT-1)
    {
        if([string isEqualToString:@""] && range.length == 1)
        {
            return TRUE;
        }
        else
        {
            return FALSE;
        }
    }
    else
    {
        return TRUE;
    }
}

Swift 4 + 2。

通过实现UITextFieldDelegate方法

ViewController: class MyViewController: UIViewController { let MAX_LENGTH = 256 @IBOutlet weak var myTextField: UITextField! override viewDidLoad() { self.myTextField.delegate = self } } Delegate: extension MyViewController: UITextFieldDelegate { func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool { let userText = textView.text ?? "" var newText = "" if range.length > 0 { let txt = NSString(string: userText) if txt.length > 0 { newText = txt.replacingCharacters(in: range, with: text) } } else { newText = userText + text } return newText.count <= MAX_LENGTH } }

斯威夫特3.0

当您粘贴字符串超过您的字符限制时，此代码工作正常。

func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
        let str = (textView.text + text)
        if str.characters.count <= 10 {
            return true
        }
        textView.text = str.substring(to: str.index(str.startIndex, offsetBy: 10))
        return false
    }

谢谢你的投票。：）

美国小妞Xamarin:

YourTextField.ShouldChangeCharacters = 
delegate(UITextField textField, NSRange range, string replacementString)
        {
            return (range.Location + replacementString.Length) <= 4; // MaxLength == 4
        };