title: How do you access url args in react-router-dom 4 when using Route render prop instead of Route component prop?
body: <p>I am using react-router-dom v 4.0.0.</p>
  
  <p>In my top-level <code>&lt;App /&gt;</code> component that renders my react router, I have three routes.  The first two work as expected, the third one does not.</p>
  
  <pre><code>render() {
      const pageMain = (
          &lt;PageMain token={this.state.token} /&gt;
      );
      const pageActivity = (
          &lt;PageActivity
              projectActivities={this.state.projectActivities}
              projectActivitiesMap={this.state.projectActivitiesMap} /&gt;
      );
      return (&lt;Router&gt;
          &lt;div&gt;
              &lt;Route
                  path="/"
                  component={PageSplash}
              /&gt;
              &lt;Route
                  path="/app"
                  render={props =&gt; pageMain}
              /&gt;
              &lt;Route
                  path="/activity/:activityId/"
                  render={props =&gt; pageActivity}
              /&gt;
          &lt;/div&gt;
      &lt;/Router&gt;);
  }
  </code></pre>
  
  <p>When I go to <strong>www.example.com/</strong>, the router directs me to my PageSplash component as expected.</p>
  
  <p>When I go to <strong>www.example.com/app</strong>, the router directs me to my PageMain component as expected.  Further, in my PageMain component, I have access to <code>this.props.token</code> as expected.</p>
  
  <p>When I go to <strong>www.example.com/activity/12345/</strong>, the router directs me to my PageActivity component as expected.  In my PageActivity component, I have access to <code>this.props.projectActivities</code> and <code>this.props.projectActivitiesMap</code> as expected.  However, I'd like to be able to access the activityId from the url, which should be 12345 in this case.  In PageActivity, I don't receive <code>this.props.params</code> as I thought, from reading countless pages of documentation.</p>
  
  <p>I started by using simple routes like my first one.  Then I needed to pass data from my top-level component to the /app route, so I begin using the <code>&lt;Route /&gt;</code> <code>render</code> prop instead of the <code>component</code> prop.  This works fine.  Then I needed to pass data and access the url param.  I can access the passed props, but my PageActivity component isn't receiving a params prop.  How do I access the activityId in my PageActivity component?</p>