用UItextField的代理方法來(lái)限制字?jǐn)?shù)或即時(shí)判斷輸入內(nèi)容有效性等問(wèn)題的時(shí)候是不能完美滿(mǎn)足需求的，這篇文章介紹另一種方法可能對(duì)你有很大啟發(fā)。因?yàn)閁ItextField和UIbutton一樣是繼承于UIControl的，所以是可以addTarget的，如下：

[textField addTarget:self action:@selector(textFieldDidChange:) forControlEvents:UIControlEventEditingChanged];

然后實(shí)現(xiàn)textFieldDidChange：的方法,這個(gè)方法在輸入或刪除每個(gè)字符的時(shí)候都會(huì)調(diào)用。

- (void)textFieldDidChange:(UITextField *)textField {
    
    NSString *toBeString = [textField.text lowercaseString];
    textField.text = toBeString;
    //限制字?jǐn)?shù)
    _limitNum = 16;
    
    //獲取高亮部分
    UITextRange *selectedRange = [textField markedTextRange];
    UITextPosition *position = [textField positionFromPosition:selectedRange.start offset:0];
    
    // 沒(méi)有高亮選擇的字，則對(duì)已輸入的文字進(jìn)行字?jǐn)?shù)統(tǒng)計(jì)和限制
    if (!position||!selectedRange)
    {
        if (toBeString.length > _limitNum)
        {
            NSRange rangeIndex = [toBeString rangeOfComposedCharacterSequenceAtIndex:_limitNum];
            if (rangeIndex.length == 1)
            {
                textField.text = [toBeString substringToIndex:_limitNum];
            }
            else
            {
                NSRange rangeRange = [toBeString rangeOfComposedCharacterSequencesForRange:NSMakeRange(0, _limitNum)];
                textField.text = [toBeString substringWithRange:rangeRange];
            }
        }
    }
    
    //commitButton 是否可以點(diǎn)擊
    if (_newPasswordTextField.text.length>5&&_confirmPasswordTextField.text.length>5&&_newPasswordTextField.text.length==_confirmPasswordTextField.text.length) {
        _commitButton.backgroundColor = SAColorByRGB(0, 124, 246);
        _commitButton.userInteractionEnabled = YES;
    }else{
        _commitButton.backgroundColor = SAColorByRGB(219, 219, 219);
        _commitButton.userInteractionEnabled = NO;
    }
    
    //實(shí)時(shí)查看密碼格式是否正確
    if (textField == _newPasswordTextField) {
        if (_newPasswordTextField.text.length>5) {
            if ([self isNumberWithLetterType:_newPasswordTextField.text]) {
                _newPasswordTextField.type = SAFloatLabeledTextFieldTypeNormal;
            }else{
                _newPasswordTextField.type = SAFloatLabeledTextFieldTypeWrong;
            }
        }else{
            _newPasswordTextField.type = SAFloatLabeledTextFieldTypeNormal;
        }
        
    }

}

/** 判斷是否是數(shù)字+字母 16位*/
- (BOOL)isNumberWithLetterType:(NSString *)string {
    NSString *regex = @"(?=.*\\d)(?=.*[a-zA-Z]).{1,16}";
    NSPredicate *pred = [NSPredicate predicateWithFormat:@"SELF MATCHES %@",regex];
    return [pred evaluateWithObject:string];
}