title: TypeError: Cannot read property 'measure' of undefined
body: <p>I have a problem with measure in react native :</p>
  
  <pre><code>checkPositionComponant = (id) =&gt; {
      this.refs.component.measure((a, b, width, height, pageX, pageY) =&gt; {
        tabTag[id].positionY = pageY;
       });
    }
  
    componentTag() {
     return tabTag.map((item, id) =&gt; {
        return(
          &lt;View key={id} style={styles.componentView} ref="component"&gt;
            { this.checkPositionComponant(id) }
          &lt;/View&gt;
        );
      });
    }
  </code></pre>
  
  <p>And my error is : TypeError: Cannot read property 'measure' of undefined</p>