list - Flutter动态更新日期和时间

Question

我是新手，这是我的第一个应用程序。我正在尝试制作待办事项列表应用，并希望在字幕中显示每个任务的剩余时间。我有一个listview，在每个元素中我都希望字幕显示分钟，向下计数到0。有人可以帮我吗？谢谢!
代码:-

class toDoListState extends State<toDoList>
{
  List<String> tasks = [];
  List<String> completedTasks = [];
  List<String> descriptions = [];
  List<bool> importance = [];
  List<String> time2completion = [];
  List<DateTime> time = [];
  
    Widget buildToDoList()
    {
        return new ListView.builder
        (
            itemBuilder: (context, index)
            {
              if(time2completion.length > 0 && index < time2completion.length && time2completion[index] != "none")
              {
                  if(time2completion[index] == "30 minutes")
                  {
                      time[index] = DateTime.now().add(Duration(minutes: 30));
                  }
                  else if(time2completion[index] == "1 hour")
                  {
                      time[index] = DateTime.now().add(Duration(hours: 1));
                  }
                  else if(time2completion[index] == "12 hours")
                  {
                      time[index] = DateTime.now().add(Duration(hours: 12));
                  }
                  else if(time2completion[index] == "1 day")
                  {
                      time[index] = DateTime.now().add(Duration(days: 1));
                  }
              }
                if(index < tasks.length)
                {
                    return row(tasks[index], descriptions[index], index);
                }
            },
        );
    }

    Widget row(String task, String description, int index)
    {                  
        return Dismissible(
        key: UniqueKey(),
        background: Container(color: Colors.red, child: Align(alignment: Alignment.center, child: Text('DELETE', textAlign: TextAlign.center, style: TextStyle(color: Colors.white, fontSize: 18),))),
        direction: DismissDirection.horizontal,
        onDismissed: (direction) {
        setState(() {
          tasks.removeAt(index);
          if(completedTasks.contains(task))
          {
              completedTasks.removeAt(index);
          }
          descriptions.removeAt(index);
          importance.removeAt(index);
        });
          Scaffold.of(context).showSnackBar(SnackBar(content: Text(task+" dismissed")));
        },
        child: CheckboxListTile(
          controlAffinity: ListTileControlAffinity.leading,
          title: Text(task, style: (completedTasks.contains(task)) ? TextStyle(decoration: TextDecoration.lineThrough) : TextStyle(),),
          subtitle: Text((time[index].difference(DateTime.now()).toString())),
          value: completedTasks.contains(task),
          onChanged: (bool value) {
           setState(() {
              if(!completedTasks.contains(task))
              {
                  completedTasks.add(task);
              }
              else
              {
                  completedTasks.remove(task);
              }
           });
          },
        ));
    }
}

Answer 1

您可以使用计时器来计算每分钟的时差。

Timer.periodic(
  Duration(minutes: 1),
  (Timer t) => setState(() {
    // your calculation here
  }),
);

以下将在有状态窗口小部件中创建一个计时器对象，并在您离开 View 时处置它:

Timer _timer;

@override
void initState() {
    _timer = Timer.periodic(
        Duration(minutes: 1),
        (Timer t) => setState(() {
            // your calculation here
        }),
    );

    super.initState();
}

@override
void dispose() {
    _timer.cancel();
    super.dispose();
}