1
我有一个类,calendar
,它从一个文件异步读取。如何等待类初始化?
// Copyright 2017 <Abhi Agarwal>
// Refer to LICENSE
// Dart Imports
import 'dart:async';
import 'dart:convert';
// Flutter Imports
import 'package:flutter/services.dart';
// Local Imports
import 'event.dart';
/// Class deals with the school-wide calendar Calendar.
class Calendar {
/// The days off in the year.
List<Event> daysOff = new List<Event>();
/// The half-days, not necessarily days off.
List<Event> halfDays = new List<Event>();
/// Vacations, extended days off.
List<Event> vactations = new List<Event>();
DateTime schoolStart;
DateTime schoolEnd;
DateTime schoolMaxEnd;
Calendar() {
_addDaysOff();
// _addHalfDays();
// _addVacations();
// _addTimes();
}
static const String filePath = "assets/calendar/";
/// Reads a JSON File specified by the Arguments and returns a Decoded Object.
Future<List<Map<String, String>>> _readJson(String fileName) async =>
await JSON.decode(await rootBundle.loadString(filePath + fileName));
Future _addDaysOff() async {
const String fileName = "days_off.json";
final List<Map<String, String>> parsed = await _readJson(fileName);
for (final Map<String, String> item in parsed) {
Event event = new Event(item["name"], DateTime.parse(item["date"]));
daysOff.add(event);
}
}
}
这工作正常,但是当我想运行一个简单的测试时出现问题。
// Copyright 2017 <Abhi Agarwal>
// Refer to LICENSE
import 'package:flutter/material.dart';
import 'definitions/calendar/calendar.dart';
void main() {
Calendar myCalendar = new Calendar();
runApp(new Center(child: new Text(myCalendar.daysOff[0].name)));
}
随着flutter run
,我得到RangeError (index): Invalid value: Valid value range is empty: 0
。这是有道理的,List在初始化时只有元素。问题是,我怎么能在那里放置一个占位符,直到数据加载完毕?
谢谢!作为一个主要使用C++的人,期货是我不能饶舌的一个领域。 –