title: refs are undefined in react native
body: <p>Im new to react-native. Im trying to read x,y co-ordinates of a view inside its parent. Using below code </p>
  
  <pre><code>componentDidMount: function() {
    setTimeout(this.measureView);
  },
  measureView: function() {
    this.refs.completeView.measure((ox, oy, width, height) =&gt; {
      this.setState({headerHeight: height});
    });
  },
  render : function(){
  return (
    &lt;TouchableHighlight onPress={() =&gt; this.props._pressRow(this.props.currentRowID)}&gt;
      &lt;View style={styles.container}
            ref="completeView"&gt;
        &lt;View style={styles.colorView}&gt;
        &lt;/View&gt;
        &lt;View style={styles.textWrapper}&gt;
          &lt;Text style={styles.text}&gt;{this.props.text}&lt;/Text&gt;
        &lt;/View&gt;
      &lt;/View&gt;
    &lt;/TouchableHighlight&gt;
  );
  },
  </code></pre>
  
  <p>Inside <code>measureView</code>, <code>this.refs</code> is always <code>undefined</code>. Why?</p>
  
  <p>I'm trying to read last view's co-ordinates into <code>ListView</code>, because for some reason I want to render the last row. So is there any other solution for this? </p>
  
  <p>Please also make a note that this class is being exported into its parent class. </p>