dart - 如何在 Dart 中逐行读取文件

Question

这个问题是 previous question 的延续.我写了下面一段代码来确定是否File.openRead()创建了一个可以逐行流式传输的 Stream。事实证明，答案是否定的。整个文件被读取，然后传递给下一个转换。我的问题是:如何在 Dart 中逐行流式传输文件？

import 'dart:async';
import 'dart:convert';
import 'dart:io';


void main(List<String> arguments) {

  Stream<List<int>> stream = new File('Data.txt').openRead();

   stream
      .transform(const Utf8InterceptDecoder())
        .transform(const LineSplitterIntercept())
          .listen((line) {
//            stdout.writeln(line);
          }).asFuture().catchError((_) => print(_));
}

int lineSplitCount = 0;

class LineSplitterIntercept extends LineSplitter {

  const LineSplitterIntercept() : super();
  // Never gets called
  List<String> convert(String data) {
    stdout.writeln("LineSplitterIntercept.convert : Data:" + data);
    return super.convert(data);
  }

  StringConversionSink startChunkedConversion(ChunkedConversionSink<String> sink) {
    stdout.writeln("LineSplitterIntercept.startChunkedConversion Count:"+lineSplitCount.toString()+ " Sink: " + sink.toString());
    lineSplitCount++;
    return super.startChunkedConversion(sink);
  }
}

int utfCount = 0;

class Utf8InterceptDecoder extends Utf8Decoder {

  const Utf8InterceptDecoder() : super();

  //never gets called
  String convert(List<int> codeUnits) {
    stdout.writeln("Utf8InterceptDecoder.convert : codeUnits.length:" + codeUnits.length.toString());
    return super.convert(codeUnits);
  }


  ByteConversionSink startChunkedConversion(ChunkedConversionSink<String> sink) {
    stdout.writeln("Utf8InterceptDecoder.startChunkedConversion Count:"+ utfCount.toString() + " Sink: "+ sink.toString());
    utfCount++;
    return super.startChunkedConversion(sink);
  }
}

Answer 1

如果需要流，您可以从 readAsLines() 的 future 创建它返回:

   Stream<List<String>> stream = 
      new Stream.fromFuture(new File('Data.txt').readAsLines());

然而，对我来说，简单地一一处理这些行看起来更简单，

  List<String> lines = new File('Data.txt').readAsLinesSync();
  for (var line in lines) {
    stdout.writeln(line); 
  }