flutter:: NoSuchMethodError: The getter 'length' was called on null-CodePudding

I created a function where the recorded voice is displayed on the screen when recording. However, if there is no record(null) in the widget, the above error occurs because length cannot be used. How can I solve this?

class Record extends StatefulWidget {
  const Record({
    Key? key,
  }) : super(key: key);

  get records => null;


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

class _RecordState extends State<Record> {
  late int _totalTime;
  late int _currentTime;
  double _percent = 0.0;
  int _selected = -1;
  bool isPlay=false;
  AudioPlayer advancedPlayer = AudioPlayer();

  @override
  Widget build(BuildContext context) {
    return ListView.builder(
      itemCount: widget.records.length,
      shrinkWrap: true,
      reverse: true,
      itemBuilder: (BuildContext context, int i) {
        return Card(
          elevation: 5,
          child: ExpansionTile(
            title: Text(
              'Record ${widget.records.length - i}',
              style: TextStyle(color: Colors.black),
            ),

CodePudding user response：

Don't return the ListView.builder if the records is null.

return widget.records == null ? SizedBox() : ListView.builder...

CodePudding user response：

Declare your class like this,

class Record extends StatefulWidget {
  const Record({
    Key? key,
    required this.records,
  }) : super(key: key);

  final List records;

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

In the above code records is a list of type List<dynamic>. If you have a specific data type,

final List<YOUR_DATA_TYPE> records;

This way, records will never be null. If records can be null,

final List<YOUR_DATA_TYPE>? records;

and use,

return ListView.builder(
      itemCount: widget.records?.length ?? 0,
      shrinkWrap: true,
      reverse: true,
      itemBuilder: (BuildContext context, int i) {
        return Card(
          elevation: 5,
          child: ExpansionTile(
            title: Text(
              'Record ${widget.records.length - i}',
              style: TextStyle(color: Colors.black),
            ),