title: How to list all posts (if any) in a select list when any post type selected from other select list
body: <p>I got success in getting all post types in a select 
   
      Select Post Type</p>
  
  <pre><code>&lt;select name="meta-select" id="select_post_types" class="form-control"&gt;  
      &lt;?php foreach ( $post_types as $post_type ) { ?&gt;
      &lt;option value="&lt;?php print $post_type; ?&gt;"&gt; &lt;?php print $post_type; ?&gt; &lt;/option&gt;
      &lt;?php } ?&gt;
  &lt;/select&gt;
  </code></pre>
  
  <p></p>
  
  <p>but I want to populate the posts of all selected post type when admin select from the top select.</p>
  
  <p>Second select is followed</p>
  
  <pre><code>&lt;select name="meta-select" id="select_post" class="form-control"&gt;  
      &lt;option value=""&gt; &lt;/option&gt;';
  
  &lt;/select&gt;
  </code></pre>