Flutter Online Test

A voting application made with Flutter uses the VoteOnce widget, which allows the user to trigger the onTapCallback function only once no matter how many times it's tapped.

The code for VoteOnce widget is given below:

class VoteOnce extends StatefulWidget {
  final Function onTapCallback;
  final String tapText;

  const VoteOnce({Key? key, required this.onTapCallback, required this.tapText}): super(key: key);

  @override
  _VoteOnceState createState() => _VoteOnceState();
}

class _VoteOnceState extends State<VoteOnce> {
  bool _wasTapped = false;
  String _displayText = "";

  @override
  void initState() {
    super.initState();
    _displayText = widget.tapText;
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      child: GestureDetector(
        onTap: () {
          if (!_wasTapped) {
            widget.onTapCallback();
          }
          setState(() {
            _wasTapped = true;
            _displayText = "Voted";
          });
        },
        child: Text("Vote for $_displayText"),
      ),
    );
  }
}

What can be concluded about the lifecycle of the VoteOnce widget?

You are making a Flutter widget to display a popup ad in your app.

The popup ad has 3 sections - title, main, and footer.

Below is the code of the widget:

Column(
    crossAxisAlignment: CrossAxisAlignment.center,
    mainAxisAlignment: MainAxisAlignment.spaceBetween,
    children: <Widget>[
      Expanded(
        flex: 2,
        child: Container(
          margin: EdgeInsets.symmetric(vertical: 5),
          width: double.infinity,
          child: Center(child: Text("Title content"))),
      ),
      Expanded(
        flex: 4,
        child: Container(
          width: double.infinity,
          child: Center(child: Text("Main content"))),
      ),
      Expanded(
        flex: 1,
        child: Container(
          width: double.infinity,
          child: Text("Footer content"))
      ),
    ]);

What can we conclude about the layout of the above widget? 

Consider the following code for a PatientNameDisplay widget in a hospital app made with Flutter:

class PatientNameDisplay extends StatefulWidget {
  final String patientName;
  final bool isAlive;
  PatientNameDisplay({this.patientName, this.isAlive});

  @override
  State<PatientNameDisplay> createState() => _PatientNameDisplayState();
}

class _PatientNameDisplayState extends State<PatientNameDisplay> {
  @override
  Widget build(BuildContext context) {
    return Text(
      (widget.patientName ?? "John Doe"),
      style: TextStyle(color: widget.isAlive ? Colors.blue : Colors.red),
    );
  }
}

The PatientNameDisplay widget defined above is used to display a patient's name. It has the following requirements:

• The widget might receive patientName as null in the case of anonymous patients.
• The widget will always receive the patient's status in the isAlive field.

Considering the requirements and the code above, what needs to be done to migrate the code to have sound null safety?