title: setState() callback argument returned a Future flutter
body: <p>When i wanted to get my token i have this error :
  setState() callback argument returned a Future.</p>
  
  <pre><code>onPressed: () {
                      setState(() async {
                        if (_formKey.currentState.validate()) {
                          Candidate candidate = new Candidate(
                              lastname: lastname,
                              firstname: firstname,
                              email: email);
                          await candidate.candidateAuth(map: candidate.toMap());
  
                          Navigator.pushReplacement(
                              context,
                              MaterialPageRoute(
                                  builder: (context) =&gt;
                                      ThemePage(candidate: candidate)));
                        }
                      });
                    },
  </code></pre>
  
  <p>The problem, when i continue in my app, i have more problems threading.</p>