How do I check the end of Stream in Dart?

Question

fellow dart programmers.

I am reading in a file using Stream as below.

Stream<List<int>> stream = new File(filepath).openRead();
stream
    .transform(UTF8.decoder)
    .transform(const LineSpilitter())
    .listen((line){
        // TODO: check if this is the last line of the file
        var isLastLine;
    });

I want to check whether the line in listen() is the last line of the file.

Answer 1

I don't think you can check if the current chunk of data is the last one.
You can only pass a callback that is called when the stream is closed.

Stream<List<int>> stream = new File('main.dart').openRead();
  stream.
  .transform(UTF8.decoder)
  .transform(const LineSpilitter())
  .listen((line) {
// TODO: check if this is the last line of the file
    var isLastLine;
  }
  ,onDone: (x) => print('done')); // <= add a second callback

Answer 2

While the answer from @Günter Zöchbauer works, the last property of streams accomplishes exactly what you are asking for (I guess the dart team added this functionality in the last 5 years).

Stream<List<int>> stream = new File('main.dart').openRead();
List<int> last = await stream.last;

But note: It is not possible to listen to the stream and use await stream.last.

This will cause an error:

StateError (Bad state: Stream has already been listened to.)