title: React-Native FlatList with custom separators
body: <p>i recently upgraded react-native to 0.44 and i am trying the new FlatList. </p>
  
  <p>I have an array(length > 200) of objects which i want to render in a list of three objects per row. When user clicks on an object, additional View is opened after this exact row where the clicked object is. Like in the google pics below: </p>
  
  <p><a href="https://i.stack.imgur.com/1IdcK.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/1IdcK.jpg" alt="enter image description here"></a></p>
  
  <p>I implemented similar behavior with the old ListView. I would calculate the row of the object on which user clicks and then render separator with required content.</p>
  
  <p>I cannot do the same for the FlatList because ItemSeparatorComponent does not have an index. Here is what i got so far:</p>
  
  <pre><code>&lt;FlatList
     data={companiesArr}
     renderItem={this.renderRowFlat}
     initialNumToRender={9}
     numColumns={3}
     windowSize={11}
     ItemSeparatorComponent={() =&gt; &lt;CategoriesSeparator /&gt;}
  /&gt;
  </code></pre>
  
  <p>Did anyone implement smth like that? please let me know.</p>
  
  <p>Additionally, the whole screen gets frozen when rendering all elements. Any workaround for that?</p>
  
  <p>Thank you!!</p>