如何保证一个textfield输入最长的文字

    NSString *lang = [self.inputTextField.textInputMode primaryLanguage]; // 键盘输入模式

    if ([lang isEqualToString:@"zh-Hans"])
    { // 简体中文输入，包括简体拼音，健体五笔，简体手写
        UITextRange *selectedRange = [self.inputTextField markedTextRange];       //获取高亮部分
        
        //获取已经确认的文字的长度
        NSInteger confirmedlength =  [self.inputTextField offsetFromPosition:self.inputTextField.beginningOfDocument
                                                                  toPosition:selectedRange.start];
        if ((nil == selectedRange) || selectedRange.isEmpty)
        {
            confirmedlength = self.inputTextField.text.length;
        }
        
        //截断超过长度的部分
        BOOL bCuttedOff = NO;
        //处理一个字符长度超过多个的情况
        if (confirmedlength >= 15)
        {
            NSRange rangeRange = [self.inputTextField.text rangeOfComposedCharacterSequencesForRange:NSMakeRange(0, 15)];
            if (self.inputTextField.text.length > rangeRange.length)
            {
                bCuttedOff = YES;
                self.inputTextField.text = [self.inputTextField.text substringSafeWithRange:rangeRange];
            }
            
        }
        if (YES == bCuttedOff)
        {
//太长了
        }

        return;
    }
    else
    {
        BOOL bCuttedOff = NO;
        if (self.inputTextField.text.length > 15)
        {
            //处理一个字符长度超过多个的情况
            NSRange rangeRange = [self.inputTextField.text rangeOfComposedCharacterSequencesForRange:NSMakeRange(0, 15)];
            if (self.inputTextField.text.length > rangeRange.length)
            {
                bCuttedOff = YES;
                self.inputTextField.text = [self.inputTextField.text substringSafeWithRange:rangeRange];
            }

        }
        if (YES == bCuttedOff)
        {
//太长了
        }
        
        return ;
    }