title: ExpandableListView - How to set divider only between parent elements
body: <p>I want to put divider only between parent elements. When i set 
  <pre><code>android:divider="@drawable/divider"</code></pre> android creates divider between parent elements, but creates divider between child elements too. When i add <pre><code>android:childDivider="@color/transparent"</code></pre> android removes the divider between child elements, but the free space between them remains. Why?
  I have tried to <pre><code>android:dividerHeight="0dp"</code></pre> but nothing happened.</p>
  
  <p>At all i want to set divider between parent elements, but i do not want any divider or empty space between child elements.</p>
  
  <p>any ideas how to do that??</p>