Flutter 延迟颤振更新列表项

我有一个从数据库加载的项目列表，问题是每个项目都需要从服务器加载一个字符串，我找不到一种方法使该字符串得到更新

逻辑

显示数据库中的位置列表（完成）

显示每个项目当前时间（问题）

屏幕截图

代码注释

Padding(
    padding: const EdgeInsets.symmetric(vertical: 1.0, horizontal: 4.0),
    child: ListView.builder(
        itemCount: locations.length,
        itemBuilder: (context, index) {
            WorldTime instance = WorldTime(name: locations[index].name, country: locations[index].country, wikipedia: locations[index].wikipedia, location: locations[index].location, flag: locations[index].flag);


            // need to use await but async/await is not allowed under `Widget build(BuildContext context)`
            instance.getTime();
            var time = instance.time;
            return Card(
                child: ListTile(
                    onTap: () {},
                    title: Text('${locations[index].location}'),
                    subtitle: Column(
                    crossAxisAlignment: CrossAxisAlignment.start,
                    children: [
                        Text(locations[index].country),
                        SizedBox(height: 5.0),
                        Text('$time'), // <-- show updated time (currently only show first load `null` and never gets updated).
                    ],
                    ),
                    leading: CircleAvatar(
                    backgroundImage: AssetImage('assets/${locations[index].flag}'),
                    ),
                ),
                );
        },
    ),
),

---

使用FutureBuilder调用instance.getTime（），因为它返回一个Future。将

文本（“$time”）

替换为以下内容：

FutureBuilder(
future:instance.getTime（），
生成器：（上下文，快照）{
if（snapshot.connectionState==connectionState.done&&instance.time！=null）{
返回文本（instance.time.toString（））；
}
返回文本（“无数据”）；
},
),

---

由于

getTime

返回

void

并将

time

分配给

WorldTime

实例，因此在

if

条件中使用

instance

。

谢谢，但它只显示

没有数据

不会将其更新到时间。getTime可能返回null。您可以发布

getTime（）

的签名吗？

instance

是未来吗？是的，它是未来，让我为您更新我的问题更新了……。编辑了我的答案，这应该可以解决您的问题。

class WorldTime {

  String location; // location name for the UI
  String time; // the time in that location
  String flag; // url to an asset flag icon
  String country;
  String wikipedia;
  String name; // name of the location to get data from server
  bool isDaytime; // true or false if day time or not

  WorldTime({this.location, this.country, this.wikipedia, this.flag, this.name});

  Future<void> getTime() async {
      var apiUrl =  Uri.https('example.com', 'api/timezone', {'name': '$name'});
      // Await the http get response, then decode the json-formatted response.
      var response = await http.get(apiUrl);
      if (response.statusCode == 200) {
        var jsonResponse = convert.jsonDecode(response.body) as Map<String, dynamic>;

        // get properties from data
        DateTime dateTime = DateTime.now().toUtc();
        String offset = jsonResponse['data']['offset'].substring(1, 3);// 07 (hour)
        String positive = jsonResponse['data']['offset'].substring(0, 1); // determine is positive or negative offset

        // create Datetime object
        String now1 = DateFormat('yyyy-MM-dd HH:mm:ss').format(dateTime);
        DateTime now = DateTime.parse(now1);
        if(positive == '+') {
          now = now.add(
              Duration(
                  hours: int.parse(offset),
                  minutes: int.parse(jsonResponse['data']['offset'].substring(4, 6)) // 00 (minutes)
              )
          );
        } else {
          now = now.subtract(
              Duration(
                  hours: int.parse(offset),
                  minutes: int.parse(jsonResponse['data']['offset'].substring(4, 6)) // 00 (minutes)
              )
          );
        }

        print(now); //2021-05-25 09:57:08.000

        // set the time property
        isDaytime = now.hour > 5 && now.hour < 18 ? true : false;
        time = DateFormat.jm().format(now);
      } else {
        print('Request failed with error:  ${response.statusCode}.');
        isDaytime = false;
        time = 'Could not get time data';
      }
  }
}