Flutter如何在List map中映射一个完整的Future对象

Question

Future<List<Future<News>>> getNewsList(skipItems) async {
    final response = await http.get(
        'https://hacker-news.firebaseio.com/v0/topstories.json?print=pretty');

    if (response.statusCode == 200) {
      // If the call to the server was successful, parse the JSON
      var responseNewsList = json.decode(response.body);
      newsList = responseNewsList as List;
      var resNewsList = (responseNewsList as List)
          .skip(skipItems)
          .take(20)
          .map((id) =>  this.fetchNewsDetails(id))
          .toList();

      return resNewsList;
    } else {
      // If that call was not successful, throw an error.
      throw Exception('Failed to load post');
    }
}

Future<News> fetchNewsDetails(id) async {
    final response = await http.get(
        'https://hacker-news.firebaseio.com/v0/item/$id.json?print=pretty');

    if (response.statusCode == 200) {
      // If the call to the server was successful, parse the JSON
      return News.fromJson(json.decode(response.body));
    } else {
      // If that call was not successful, throw an error.
      throw Exception('Failed to load post');
    }
}

So as the code you can see that I try to get a list of top stories post but the response only return me a list of ids, so I will need call another api to get the post detail, in the way above I will need to use twice Future Builder for display the content, the way works but is there anyway for me to wait the response back and have the post result in the mapping function?

Answer 1

I assume you want

await Stream.fromIterable((responseNewsList as List)
      .skip(skipItems)
      .take(20))
      .asyncMap((id) =>  this.fetchNewsDetails(id))
      .toList();

https://api.dartlang.org/stable/2.1.0/dart-async/Stream/asyncMap.html

Answer 2

An alternative approach to Günter's is to replace the manual creation of a stream and make it more explicit you actually just want the completed Futures instead:

await Future.wait((responseNewsList as List)
    .skip(skipItems)
    .take(20)
    .map((id) => fetchNewsDetails(id)))
  ).toList();