我正在写一个Flutter应用程序，其中一个要求是离线保存数据以便在没有互联网的情况下读取它，但是当我从Sqflite的数据库加载时出现问题，我收到此错误：type '_Type' is not a subtype of type 'FutureOr<Verse>'。我究竟做错了什么？我正在使用BLOC Pattern。
当我检查res变量形式getDailyVerse函数时，我看到是空的，但在getAllVerse中，我看到我得到了所有经文，但在ListView中我看不到是否加载。
这是我的模特：
import 'dart:async';
import 'dart:io';
import 'package:path/path.dart';
import 'package:path_provider/path_provider.dart';
import 'package:sqflite/sqflite.dart';
import 'package:http/http.dart' show Client;
import 'dart:convert';
import '../models/verse.dart';
class VerseProvider {
VerseProvider._();
static final VerseProvider db = VerseProvider._();
Client client = Client();
final String _urlApi = "https://arcane-tundra-45231.herokuapp.com";
Database _database;
Future<Database> get database async {
if (_database != null) return _database;
_database = await initDB();
return _database;
}
initDB() async {
Directory documentsDirectory = await getApplicationDocumentsDirectory();
String path = join(documentsDirectory.path, "DailyVerse.db");
return await openDatabase(
path,
version: 1,
onOpen: (db) {},
onCreate: (Database db, int version) async {
await db.execute("CREATE TABLE Verse ("
"id INTEGER PRIMARY KEY, "
"day INTEGER, "
"text TEXT, "
"text_es TEXT, "
"human_reference TEXT, "
"human_reference_es TEXT, "
"url TEXT, "
"url_es TEXT, "
"image_url TEXT"
")");
}
);
}
newVerse(Verse verse) async {
final db = await database;
// var res = await db.rawInsert(
// "INSERT INTO Verse (id, day, text, text_es, human_reference, human_reference_es, url, url_es, image_url)"
// " VALUES (${verse.id}, ${verse.day}, ${verse.text.replaceAll("'", "`")}, ${verse.textEs.replaceAll("'", "`")}, ${verse.humanReference.replaceAll("'", "`")}, ${verse.humanReferenceEs.replaceAll("'", "`")}, ${verse.url}, ${verse.urlEs}, ${verse.imageUrl})"
// );
var res = await db.insert(
"Verse",
verse.toMap(),
conflictAlgorithm: ConflictAlgorithm.replace
);
return res;
}
Future<Verse> getDailyVerse() async {
final db = await database;
final today = DateTime(DateTime.now().year, 1, 1, 0,).difference(DateTime(DateTime.now().year, 1, 1, 0, 0)).inDays;
var res = await db.query("Verse", where: "day = ?", whereArgs: [today]);
print(res);
return res.isNotEmpty ? Verse.fromJson(res.first) : Null;
}
Future<VerseList> getAllVerse() async {
final db = await database;
var res = await db.query("Verse");
print(res);
return res.isNotEmpty ? VerseList.fromJson(res) : Null;
}
Future<Verse> fetchDailyVerse() async {
final response = await client.get(_urlApi + "/api/v0/verses/day");
print(response.body.toString());
print(DateTime.now());
print(DateTime.now());
print(DateTime(DateTime.now().year, 1, 1, 0,).difference(DateTime(DateTime.now().year, 1, 1, 0, 0)).inDays);
if (response.statusCode == 200) {
var jsonResponse = json.decode(response.body);
return Verse.fromJson(jsonResponse['data']);
} else {
throw Exception('Failed to Load Verse');
}
}
Future<VerseList> fetchAllVerses() async {
final response = await client.get(_urlApi + "/api/v0/verses/");
if (response.statusCode == 200) {
var jsonResponse = json.decode(response.body);
return VerseList.fromJson(jsonResponse['data']);
} else {
throw Exception('Failed to load Verses');
}
}
}
这是当我在本地加载数据时调用它：
import 'dart:async';
import '../resources/verse_provider.dart';
import '../models/verse.dart';
import '../resources/config_provider.dart';
class Repository {
final verseProvider = VerseProvider.db;
fetchDailyVerse() async {
bool isOfflineSaved = false;
ConfigProvider().getSaveOffline().then((value) => isOfflineSaved = value ).then((onValue) async {
if (isOfflineSaved) {
return await verseProvider.getDailyVerse();
} else {
return await verseProvider.fetchDailyVerse();
}
});
}
fetchAllVerses() async {
bool isOfflineSaved = false;
ConfigProvider().getSaveOffline().then((value) => isOfflineSaved = value ).then((onValue) async {
if (isOfflineSaved) {
return await verseProvider.getAllVerse();
} else {
return await verseProvider.fetchAllVerses();
}
});
}
}
这是我在本地保存的时间：
Future saveVerseOffline() async {
// Show Dialog.waiting
showDialog(
context: context,
barrierDismissible: false,
builder: (context) {
return new Dialog(
child: new Row(
mainAxisSize: MainAxisSize.min,
children: [
new CircularProgressIndicator(),
new Text("Procesando..."),
],
),
);
},
);
// 1. Fetch the verses
final verses = fetchVerses();
print(verses);
// 2. Check if there any data saved
if (isDataSavedOnDB) {
// 3. If there are data. Do not save
new Future.delayed(new Duration(seconds: 2), () {
Navigator.pop(context); //pop dialog
});
} else {
print("something");
// 4. If there are not data. Begin to Save.
await verses.then((onValue) async {
int i = 0;
onValue.verses.forEach((f){
print("countiing $i");
// 5. Invocate the new verses and save it.
print(f);
VerseProvider.db.newVerse(f);
i += 1;
});
// 6. Dismmiss Dialog.
new Future.delayed(new Duration(seconds: 2), () {
Navigator.pop(context); //pop dialog
}).then((onValue) async {
await ConfigProvider().setSaveOffline(true).then((onValue){
setState((){
isDataSavedOnDB = true;
});
});
});
});
}
}
首先，我正在调试代码，我发现了
final today = DateTime(DateTime.now().year, 1, 1, 0,).difference(DateTime(DateTime.now().year, 1, 1, 0, 0)).inDays;
它返回0
ConfigProvider().getSaveOffline().then((value) => isOfflineSaved = value ).then((onValue) async {
if (isOfflineSaved) {
return await verseProvider.getAllVerse();
} else {
return await verseProvider.fetchAllVerses();
}
});
返回丢失，这导致无法渲染。我已经解决了这个问题：
return ConfigProvider().getSaveOffline().then((value) => isOfflineSaved = value ).then((onValue) async {
if (isOfflineSaved) {
return await verseProvider.getAllVerse();
} else {
return await verseProvider.fetchAllVerses();
}
});
Future<VerseList> getAllVerse() async {
final db = await database;
var res = await db.query("Verse");
print(res);
return res.isNotEmpty ? VerseList.fromJson(res) : Null;
}
就像上面的方法，你不能返回Null，因为Null不是VerseList类型，你应该将Null更改为VerseList()，或者你可以将Future<VerseList>更改为Future<dynmic>。