title: React-Native Flatlist getItemLayout with dynamic item height
body: <p>I am trying to implement a scrollToIndex function on a flatlist so that it scrolls to a specific item when it renders. The issue I am running into is that the items the flatlist renders have a <code>minHeight</code>. The issue with that is, the flatlist needs to implement a function to calculate the offset for every element. I cant think of a way to <code>pre-render</code> the flatlist and get the height of every item in it. As you can see I am simply adding a static number for the offset and that is not what I need. </p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>&lt;FlatList
    data={data}
    renderItem={this.renderItem}
    getItemLayout={(dat, index) =&gt; {
      let offset = 0;
      for (let i = 0; i &lt; index; i++) {
        if (data[i].headerText) {
          offset += 33;
        } else {
          offset += 80;
        }
      }
      return { length: 0, offset, index }
    }
    }
    ref={(ref) =&gt; { this.flatListRef = ref; }}
  /&gt;</code></pre>
  </div>
  </div>
  </p>