dart - RxDart，将列表的每个项目映射到来自永无止境的流的另一个对象

Question

我一直在试图找到一种很好的方法来做到这一点，但是我没有运气。

这是问题的简化版本:

import 'package:rxdart/rxdart.dart';


/// Input a list of integers [0,1,2,3,4]
/// map each of those integers to the corresponding index in the map
/// if the map updates, the output should update too.
///
/// The output should be a list of Strings:
/// ["Hi from 1", "Hi from 2"; "Hi from 3", "Hi from 4", "Hi from 5"]
BehaviorSubject<Map<int, String>> subject = BehaviorSubject(
    seedValue: {
      1: "Hi from 1",
      2: "Hi from 2",
      3: "Hi from 3",
      4: "Hi from 4",
      5: "Hi from 5",
    }
);

void main() {
  Observable.fromIterable([1, 2, 3, 4, 5])
      .flatMap((index) => subject.stream.map((map) => map[index]))
      .toList().asObservable()
      .listen((data) {
    print("List of data incoming $data");
  });
}

运行此命令时，不会打印任何内容。这是因为主题从未完成，因此 toList()从未完成构建列表。

例如，用 Observable.just(index + 2)替换主题确实可行，因为Observable已完成并且 toList()能够收集它们。

但是预期的行为是，每次更改主题时，示例都应发出新的字符串列表。

任何帮助，将不胜感激，

谢谢!

Answer 1

您可能想改用combineLatest

BehaviorSubject<Map<int, String>> subject = BehaviorSubject(seedValue: {
  1: "Hi from 1",
  2: "Hi from 2",
  3: "Hi from 3",
  4: "Hi from 4",
  5: "Hi from 5",
});

void main() {
  Observable.combineLatest2(
      Observable.just([1, 2, 3, 4, 5]), subject.stream, combiner)
    ..listen(
      (data) {
        print("List of data incoming $data");
      },
    );
}

Iterable<String> combiner(List<int> indexes, Map<int, String> map) {
  return indexes.map((index) => map[index]);
}