How to store csv data in a list - dart

Question

I want to read a csv file and store the content in a list of abjects. So I created the respective object and made an inputstream to read the file. But when I try to acces the list from outside of the function it's empty, so I thing, that the data is stored in a copy of listOfStocks and not directly in the list, like I want. So how can I store the content in the list?
import 'dart:io';
import 'dart:async';
import 'dart:convert';
main(List arguments) {
final File file = new File("../Data/In.List.toDart.csv");
Stream<List> inputStream = file.openRead();
List<Stock> listOfStocks = new List();
inputStream
.transform(utf8.decoder)
.transform(new LineSplitter())
.listen((String line) {
List row = line.split(',');
Stock stock = new Stock();
stock.setSymbol(row[0]);
stock.setDesc(row[1]);
stock.setExchange(row[2]);
listOfStocks.add(stock);
print(listOfStocks.length);
},
onDone: () { print('All read.'); },
onError: (e) { print(e.toString()); });
print(listOfStocks.length);
}
class Stock {
String symbol;
String desc;
String exchange;
void setSymbol(String symbol) {
this.symbol = symbol;
}
void setDesc(String desc) {
this.desc = desc;
}
void setExchange(String exchange) {
this.exchange = exchange;
}
String getSymbol() {
return symbol;
}
String getDesc() {
return desc;
}
String getExchange() {
return exchange;
}
}

Answer 1

The inputStream is asynchronous, so it will take some time before the file has been read.
The inputStream.transform(...).transform(...).listen(...) call completes immediately, then the stream will emit events when something has been read from the disk, and the listOfStocks will be gradually populated.
If you need the content of the list "immediately", that is: before you do anything else, you will have to block until the list is fully populated.
You can do this in two ways:
Read the file synchronously. This makes the operating system block until the file has been read completely into memory.
var content = file.readAsStringSync(); // Defaults to UTF-8 decoding.
for (var line in LineSplitter.split(content))
...
lineOfStocks.add(stock);
}
print(listOfStocks.length);
Read the file asynchronously, but wait for the transformation to complete:
main(List arguments) async {
...
await inputStream
.transform(utf8.decoder)
.transform(const LineSplitter())
.forEach((String line) { // Use forEach instead of listen
...
listOfStocks.add(stock);
});
print(listOfStocks.length);
}
I you use forEach instead of listen, it returns a future which completes
when the stream is done. With listen, you get a done event that you have
to handle manually.