从未来中返回列表

本文介绍了从未来中返回列表的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

我是flutter和异步编程的新手。我需要执行以下操作：

Hi i'm new to flutter and asynchronous programming. i need to do something like this:

List<Widget> usersProfiles = [];
      getUsers('DcofOiHWcjbjD0i18miW').then((user) {
        user.forEach((u) {
          usersProfiles.add(new ListTile(
            leading: CircleAvatar(
              backgroundImage: AssetImage(u.profilePicture),
            ),
            trailing: u.icon,
            title: new Text(u.name),
            onTap: () {
              Navigator.push(context,
                  new MaterialPageRoute(builder: (context) => new Home()));
            },
          ));
        });
      });

但 usersProfiles 返回空

我会非常感激

推荐答案

我建议使用或（适用于流），它为您带来了布局性能上的优势，并提供了轻松添加负载的工具和错误小部件。
看起来可能像这样：

I would recommend either a FutureBuilder or StreamBuilder (for streams) which gives you layout performance benefits and also tools to easily add loading and error widgets.It could look like following:

Future<List<User>> usersFuture = getUsers('DcofOiHWcjbjD0i18miW');

将future创建为成员变量，因此您只需提取一次（以防方法每次都启动一个新的future）您称呼它的时间）。然后在FutureBuilder中使用它。

Create the future as member variable so you only fetch once (in case the method initiates a new future each time you call it). And then use it inside a FutureBuilder.

FutureBuilder<List<User>>(
    future: usersFuture,
    builder: (context, snapshot) {
      if(snapshot.connectionState != ConnectionState.done) {
        // return: show loading widget
      }
      if(snapshot.hasError) {
        // return: show error widget
      }
      List<User> users = snapshot.data ?? [];
      return ListView.builder(
        itemCount: users.length,
        itemBuilder: (context, index) {
          User user = users[index];
          return new ListTile(
            leading: CircleAvatar(
              backgroundImage: AssetImage(user.profilePicture),
            ),
            trailing: user.icon,
            title: new Text(user.name),
            onTap: () {
              Navigator.push(context,
                  new MaterialPageRoute(builder: (context) => new Home()));
            },
          );
      });
  });

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