嗨,我是颤振和异步编程的新手。我需要做这样的事情:
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()));
},
));
});
});
but usersProfiles
回报null
我将非常感激
我会推荐一个未来建造者 https://docs.flutter.io/flutter/widgets/FutureBuilder-class.html or 流生成器 https://docs.flutter.io/flutter/widgets/StreamBuilder-class.html(对于流)它为您提供布局性能优势以及轻松添加加载和错误小部件的工具。
它可能如下所示:
Future<List<User>> usersFuture = getUsers('DcofOiHWcjbjD0i18miW');
将 future 创建为成员变量,这样您只需获取一次(以防每次调用该方法时都会启动一个新的 future)。然后在 FutureBuilder 中使用它。
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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