anchor.diff:    DateTime _toDateTime = new DateTime.now();
     bool _allDayValue = false;
     bool _saveNeeded = false;
  +  bool _hasLocation = false;
  +  bool _hasName = false;
  +  String _eventName;
   
     Future<bool> _onWillPop() async {
  +    _saveNeeded = _hasLocation || _hasName || _saveNeeded;
       if (!_saveNeeded)
         return true;
   
  
positive.code: 
      return new Scaffold(
        appBar: new AppBar(
          title: const Text('New event'),
          actions: <Widget> [
            new FlatButton(
              child: new Text('SAVE', style: theme.textTheme.body1.copyWith(color: Colors.white)),
  
negative.code:           children: <Widget>[
              new Container(
                padding: const EdgeInsets.symmetric(vertical: 8.0),
                alignment: Alignment.bottomLeft,
                child: new TextField(
                  decoration: const InputDecoration(
                    labelText: 'Event name',
                    filled: true
                  ),
                  style: theme.textTheme.headline,
                  onChanged: (String value) {
                    setState(() {
                      _hasName = value.isNotEmpty;
                      if (_hasName) {
                        _eventName = value;
                      }
                    });
                  }
                )
              ),
              new Container(
                padding: const EdgeInsets.symmetric(vertical: 8.0),
                alignment: Alignment.bottomLeft,
                child: new TextField(
                  decoration: const InputDecoration(
                    labelText: 'Location',
                    hintText: 'Where is the event?',
                    filled: true
                  ),
                  onChanged: (String value) {
                    setState(() {
                      _hasLocation = value.isNotEmpty;
                    });
                  }
                )
              ),
              new Column(
                crossAxisAlignment: CrossAxisAlignment.start,
  