iOS中textfield有效限制输入长度

#pragma mark - textField代理方法- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string{    NSInteger existedLength = textField.text.length;    NSInteger selectedLength = range.length;    NSInteger replaceLength = string.length;    NSInteger pointLength = existedLength - selectedLength + replaceLength;    if ([textField isEqual:_phoneTF]) {        //不允许超过11位         if (pointLength > 11) {            return NO;        }        return YES;    }    return NO;}