title: React pass function to child parent not re rendering
body: <p>I have the following function:</p>
  
  <pre><code>update() {
      this.currentItem = [];
      //...Populate currentItem
  
      this.setState({
        currentItem
      });
    }
  </code></pre>
  
  <p>Which renders on the page like this;</p>
  
  <pre><code>render() {
     const { currentItem } = this.state;
     return {currentItem}
  }
  </code></pre>
  
  <p>I then pass this function into a child component, like this:</p>
  
  <pre><code>&lt;Component
     update={this.update.bind(this)}
  /&gt;
  </code></pre>
  
  <p>and then call it like this in my child component:</p>
  
  <pre><code>let { update } = this.props;
  if (typeof update === "function")
    update();
  </code></pre>
  
  <p>The problem is that the update function does not re render the content I am updating on the parent page. As far as I understand this, whenever setState is called, render also gets called. render() does seem to be getting called, but it does not seem to display the updated value - why is this, and how can I resolve it?</p>
  
  <p>I guess it could be to do with the fact that it is coming from a child component?</p>
  
  <p>I have tried forceUpdate, but it does not re render the component either - what am I missing?</p>