斯威夫特4

import UIKit

private var kAssociationKeyMaxLength: Int = 0

extension UITextField {
    
    @IBInspectable var maxLength: Int {
        get {
            if let length = objc_getAssociatedObject(self, &kAssociationKeyMaxLength) as? Int {
                return length
            } else {
                return Int.max
            }
        }
        set {
            objc_setAssociatedObject(self, &kAssociationKeyMaxLength, newValue, .OBJC_ASSOCIATION_RETAIN)
            addTarget(self, action: #selector(checkMaxLength), for: .editingChanged)
        }
    }
    
    @objc func checkMaxLength(textField: UITextField) {
        guard let prospectiveText = self.text,
            prospectiveText.count > maxLength
            else {
                return
        }
        
        let selection = selectedTextRange
        
        let indexEndOfText = prospectiveText.index(prospectiveText.startIndex, offsetBy: maxLength)
        let substring = prospectiveText[..<indexEndOfText]
        text = String(substring)
        
        selectedTextRange = selection
    }
}

编辑:内存泄漏问题修复。

快速2.0 +

首先，为这个过程创建一个类。我们称之为StringValidator.swift。

然后把下面的代码粘贴进去。

import Foundation

extension String {

func containsCharactersIn(matchCharacters: String) -> Bool {
let characterSet = NSCharacterSet(charactersInString: matchCharacters)
return self.rangeOfCharacterFromSet(characterSet) != nil
}

func containsOnlyCharactersIn(matchCharacters: String) -> Bool {
let disallowedCharacterSet = NSCharacterSet(charactersInString: matchCharacters).invertedSet
return self.rangeOfCharacterFromSet(disallowedCharacterSet) == nil
}


func doesNotContainCharactersIn(matchCharacters: String) -> Bool {
let characterSet = NSCharacterSet(charactersInString: matchCharacters)
return self.rangeOfCharacterFromSet(characterSet) == nil
}

func isNumeric() -> Bool
{
let scanner = NSScanner(string: self)
scanner.locale = NSLocale.currentLocale()

return scanner.scanDecimal(nil) && scanner.atEnd
}

}

现在保存类.....

使用. .

现在转到你的viewController.swift类，并将你的文本字段的outlet设为..

@IBOutlet weak var contactEntryTxtFld: UITextField! //First textfield
@IBOutlet weak var contactEntryTxtFld2: UITextField!   //Second textfield

现在转到textfield的shouldChangeCharactersInRange方法，像下面这样使用。

func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool {
    if string.characters.count == 0 {
        return true
    }
    let latestText = textField.text ?? ""
    let checkAbleText = (latestText as NSString).stringByReplacingCharactersInRange(range, withString: string)


    switch textField {

    case contactEntryTxtFld:
        return checkAbleText.containsOnlyCharactersIn("0123456789") && prospectiveText.characters.count <= 5

    case contactEntryTxtFld2:
        return checkAbleText.containsOnlyCharactersIn("0123456789") && prospectiveText.characters.count <= 5

    default:
        return true
    }

}

不要忘记设置文本字段的委托协议/方法。

让我来解释一下……我正在使用我在另一个类中写的字符串的简单扩展过程。现在我只是调用那些扩展方法从另一个类，我需要他们通过添加检查和最大值。

功能……

它将设置特定文本字段的最大限制。 它将为特定文本字段设置接受的键的类型。

类型……

containsOnlyCharactersIn //只接受字符。

containsCharactersIn //接受字符组合

doesNotContainsCharactersIn //不接受字符

希望这对你有所帮助.... 谢谢. .

我模拟实际的字符串替换，计算未来字符串的长度:

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {

    NSString *newString = [textField.text stringByReplacingCharactersInRange:range withString:string];

    if([newString length] > maxLength)
       return NO;

    return YES;
}

现在你想要多少字符，只要给值就行了

 - (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range   replacementString:(NSString *)string {
     NSUInteger newLength = [textField.text length] + [string length] - range.length;
     return (newLength > 25) ? NO : YES;
  }

使用接口构建器，您可以在任何函数中链接并获得“编辑更改”的事件。 现在你可以检查长度

- (IBAction)onValueChange:(id)sender 
{
    NSString *text = nil;
    int MAX_LENGTH = 20;
    switch ([sender tag] ) 
    {
        case 1: 
        {
            text = myEditField.text;
            if (MAX_LENGTH < [text length]) {
                myEditField.text = [text substringToIndex:MAX_LENGTH];
            }
        }
            break;
        default:
            break;
    }

}

下面的代码类似于sickp的答案，但是正确地处理复制-粘贴操作。如果尝试粘贴超过限制的文本，下面的代码将截断文本以符合限制，而不是完全拒绝粘贴操作。

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
    static const NSUInteger limit = 70; // we limit to 70 characters
    NSUInteger allowedLength = limit - [textField.text length] + range.length;
    if (string.length > allowedLength) {
        if (string.length > 1) {
            // get at least the part of the new string that fits
            NSString *limitedString = [string substringToIndex:allowedLength];
            NSMutableString *newString = [textField.text mutableCopy];
            [newString replaceCharactersInRange:range withString:limitedString];
            textField.text = newString;
        }
        return NO;
    } else {
        return YES;
    }
}