title: Why is there double with the same key in my React-Native FlatList?
body: <p>I'm trying to get an object described at the following endpoint : 
  <a href="https://api.cosmicjs.com/v1/67302ce0-7681-11e9-8193-4bd8888ec129/objects?pretty=true&amp;hide_metafields=true" rel="nofollow noreferrer">https://api.cosmicjs.com/v1/67302ce0-7681-11e9-8193-4bd8888ec129/objects?pretty=true&amp;hide_metafields=true</a></p>
  
  <p>As you will notice there is a _id field with a unique identifier.</p>
  
  <p>So why do i get : </p>
  
  <blockquote>
    <p>"Warning: Encountered two children with the same key, <code>:</code>. Keys should
    be unique so that components maintain their identity across updates.
    Non-unique keys may cause children to be duplicated and/or omitted —
    the behavior is unsupported and could change in a future version."</p>
  </blockquote>
  
  <p>Here is my FlatList render :</p>
  
  <pre><code>render() {   
      if(this.props.dataToDisplay.objects){
          console.log(typeof(this.props.dataToDisplay.objects))
          console.log(this.props.dataToDisplay.objects)
          this.props.dataToDisplay.objects.forEach((item)=&gt;{
              console.log(item)
          })
  
          return (
              &lt;View style={[{backgroundColor: this.state.backgroundColor},styles.container]}&gt;
                  &lt;FlatList
                      data={this.props.dataToDisplay.objects}
                      keyExtractor={(item, index)=&gt;{item._id.toString()}}
                      renderItem={({item})=&gt;{
                          &lt;Text id={item._id}&gt;{item.title}&lt;/Text&gt;
                      }}
                  /&gt;
              &lt;/View&gt;
          );
  }
   else {
  
      return (
          &lt;View style={[{backgroundColor: 
  this.state.backgroundColor},styles.container]}&gt;
              &lt;Text&gt;Loading elements.&lt;/Text&gt;
          &lt;/View&gt;
        );
      }
    }
  }
  </code></pre>
  
  <p>Could there be a problem with the keyExtractor ?
  I tried with keyExtractor={(item, index)=>{item._id}} with no results...</p>
  
  <p>Thanks for your time.</p>