title: Enable Button on flutter only if Checkbox is " checked"
body: <p>Hello guys I have registration form with checkbox to be enabled in order to allow registration.
  I need my user to do checkbox checked to have button enabled otherwise an tooltip will be shown.. like... &quot; u need to accept terms and condition to register... &quot;
  This is the part of the CheckBox:</p>
  <pre><code>Row(
                    mainAxisAlignment: MainAxisAlignment.center,
                    children: &lt;Widget&gt;[
                      Theme(
                        data: ThemeData(unselectedWidgetColor: Colors.white,),
                        child: Checkbox(
                          focusColor: Colors.lightBlue,
                          activeColor: Colors.orange,
                          value: rememberMe,
                          onChanged: (newValue) {
                            setState(() {
                              rememberMe = (newValue);
                            });
                          },
                        ),
                      ),
                      RichText(
                        text: TextSpan(children: [
                          TextSpan(
                            text: 'Accetto le condizioni e ',
                            style: TextStyle(fontSize: 10),
                          ),
                          TextSpan(
                            text: 'il trattamento dei dati personali ',
                            style: TextStyle(fontSize: 10,decoration: TextDecoration.underline,),
                          ),
                        ]),
                      )
                    ],
                  ),
  
  </code></pre>
  <p>and this the &quot;registration Button&quot;</p>
  <pre><code>ButtonTheme(
                    minWidth: 100,
                    height: 50.0,
                    child: RaisedButton(
                      shape: RoundedRectangleBorder(
                        borderRadius: BorderRadius.circular(5.0),
                      ),
                      elevation: 10,
                      onPressed: () async {
  
                        setState(() {
                          showSpinner = true;
                        });
                        try {
                          final newUser =
                              await _auth.createUserWithEmailAndPassword(
                                  email: email, password: password);
                          if (newUser != null) {
                            Navigator.push(
                              context,
                              MaterialPageRoute(builder: (context) =&gt; HomePage()),
                            );
                          }
                          setState(() {
                            showSpinner = false;
                          });
                        } catch (e) {
                          print(e);
                        }
                      },
                      color: Color(0xFF1f2032),
                      child: Text(
                        'SIGNUP',
                        style: TextStyle(fontSize: 18, color: Colors.white),
                      ),
                    ),
                  ),
  
  </code></pre>