how the loop work in function.php wordpress

Question

     add_action( 'wp_ajax_nopriv_Paper3_submit', 'Paper3_submit' );
        add_action( 'wp_ajax_Paper3_submit', 'Paper3_submit' );    

        function Paper3_submit() {  
     $zxdArgs2 = array(
           'post_type' => 'post',
           'post__in'  => array(3),
        );  
            $zxdQuery = new WP_Query( $zxdArgs2 );
                $zxdQuery->query($zxdArgs2);
                echo 'ok';//this line will show up
                if ($zxdQuery->have_posts()){
                while ($zxdQuery->have_posts()) { 
                $zxdQuery->the_post();
                  echo "002";//never show up
?>
                <li class="zxd_ajax_cc_li><a href="<?php the_permalink();?>" title="Permanent Link To <?php the_title_attribute();?>" ><?php the_title();?></a></li>
                <?php 
                echo "001" ;//never show up
                }
                }
                echo "NO" ;//this line shows up too
                wp_reset_postdata();
               echo 'NO2' ; //this line shows up too
                exit;
            }

i am working on a ajax thing, the functions works,i get the response ,like "okNONO2". but it seems the loop content do not show,you can see the code above,the "echo" line outside the loop all works,inside ones do not work.how is that?hope someone tell me,thank you.

Answer 1

I know it now,the loop works fine,the psoblem is I use wrong query.that is all.

'category__in'  => array(3),

i want query this.that is why.