iOS UITextField 输入字数限制的实现

首先你的ViewController须要实现 UITextFieldDelegate 代理，

其次，须要字数限制的UITextField实例的代理要设置成 self（ViewController）

而后实现下列代理方法：

Objective—C

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

    if(range.length + range.location > textField.text.length)

    {

        return NO;

    }

    NSUInteger newLength = [textField.text length] + [string length] - range.length;

    return newLength <= 5;//最大字数长度

}

swift：

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

    let currentCharacterCount = textField.text?.characters.count ?? 0
    if (range.length + range.location > currentCharacterCount){
        return false
    }
    let newLength = currentCharacterCount + string.characters.count - range.length
    return newLength <= 25
}