title: Using array index on FlatList in React Native
body: <p>I have an array of objects as follows. None of the objects has a unique key.</p>
  
  <pre><code>[
     {
         data1: "text1",
         data2: "text2"
     },
     {
         data1: "text3",
         data2: "text4"
     }
  ]
  </code></pre>
  
  <p>I have a FlatList defined as follows:</p>
  
  <pre><code>&lt;FlatList
  
       data={this.state.items}
       renderItem={this.renderItem}
  /&gt;
  </code></pre>
  
  <p>I have also tried adding:</p>
  
  <pre><code> keyExtractor={this._keyExtractor}
  </code></pre>
  
  <p>but I still get the same message. I am not sure what the above <code>this._keyExtractor</code> is supposed to be doing. Is it a built in function to pull the index or a function that I am supposed to create myself?</p>
  
  <p>What am I doing wrong and how can I just use the array index as my unique key?</p>