title: How can I use FutureBuilder after getting userId?
body: <p>If you want to get a list of users,
  just set <code>Firestore.instance.collection("users").snapshots()</code> to the Futurebuilder's <code>future:</code> </p>
  
  <p>But, how can I use <code>userDataRef()</code> to get user's data based on userId using FutureBuilder?</p>
  
  <pre><code>  Future&lt;Stream&lt;DocumentSnapshot&gt;&gt; userDataRef() async {
      final FirebaseUser user = await auth.currentUser();
  
      return Firestore.instance
          .collection("users")
          .document(user.uid).snapshots();
    }
  </code></pre>
  
  <p>This is my FutureBuilder.
  trying to display users favorite foods.</p>
  
  <pre><code>  FutureBuilder(
      future: Database.shared.userDataRef(),
      builder: (BuildContext context, snapshot) {
        if (!snapshot.hasData) {
          return Text("Error");
        }
        final doc = snapshot.data.documents;
        final List favoriteFoods = doc["favorite_foods"];
  
  
        return Text(favoriteFoods.toString());
      },
  </code></pre>
  
  <p>Any advice will be appreciated.</p>
  
  <p>Thanks.</p>