我的设备没有互联网连接时,我试图捕获该错误。我建立了2种将来的方法,一种是导入json,另一种是查看数据库。我有一个Future构建器,该构建器假定在构建网格视图之前要等待两个Future完成,但是由于连接错误,似乎offlineFlashCardList被过早调用。知道如何在调用快照错误之前让它等待两个期货完成吗?
import 'package:flutter/material.dart';
import 'package:flutter/foundation.dart';
import 'package:baby_sound/strings.dart';
import 'package:baby_sound/objects/flashCardList.dart';
import 'package:cached_network_image/cached_network_image.dart';
import 'dart:async' show Future;
import 'dart:convert';
import 'package:baby_sound/database/database.dart';
import 'package:baby_sound/objects/network.dart';
import 'package:http/http.dart' as http;
class GridViewWidget extends StatefulWidget{
@override
createState() => new GridViewState();
}
class GridViewState extends State<GridViewWidget>{
List<FlashCardList> flashCardList;
List<FlashCardList> offlineFlashCardList;
Future<List<FlashCardList>> fetchFlashCardList() async{
debugPrint("before response");
List<FlashCardList> tempFlashCardList;
final response = await http.get('some json url');
//checkConnection(url).then((response){
debugPrint ("after database load, response code: ${response.statusCode}");
if (response.statusCode == 200) {
var data = json.decode(response.body);
var flashCardListData = data["FlashCardList"] as List;
tempFlashCardList = flashCardListData.map<FlashCardList>((json) => FlashCardList.fromJson(json)).toList();
for (int i = 0; i < tempFlashCardList.length; i++){
debugPrint("DBProvider listID: ${await DBProvider.db.getFlashCardList(tempFlashCardList[i].flashCardListID)}, flashCardID: ${tempFlashCardList[i].flashCardListID}");
if (await DBProvider.db.getFlashCardList(tempFlashCardList[i].flashCardListID) == null){
DBProvider.db.newFlashCardList(tempFlashCardList[i]);
debugPrint("Adding ${tempFlashCardList[i].name}}}");
} else {
DBProvider.db.updateFlashCardList(tempFlashCardList[i]);
debugPrint("Updating ${tempFlashCardList[i].name}, getFlashCardList: ${DBProvider.db.getFlashCardList(tempFlashCardList[i].flashCardListID)}");
}
}
flashCardList = tempFlashCardList;
debugPrint("Standard flashCardList Size: ${flashCardList.length}");
}
debugPrint("flashCardList Size Before Return: ${flashCardList.length}");
return flashCardList;
}
Future<List<FlashCardList>> fetchFlashCardListFromDB() async{
offlineFlashCardList = await DBProvider.db.getAllFlashCardListFromDB();
debugPrint("fetchFromDB size: ${offlineFlashCardList.length}");
return offlineFlashCardList;
}
@override
void initState(){
debugPrint ('debug main.dart');
super.initState();
}
@override
Widget build(BuildContext context){
return new Scaffold(
appBar: new AppBar(
centerTitle: true,
title: new Text(Strings.pageTitle),
),
body: FutureBuilder<List<FlashCardList>>(
future: new Future(() async{
await fetchFlashCardList();
await fetchFlashCardListFromDB();
}),
builder: (BuildContext context, AsyncSnapshot<List<FlashCardList>> snapshot) {
if (snapshot.connectionState == ConnectionState.done) {
if (snapshot.hasError) {
debugPrint("Snapshot has error: ${snapshot.error}");
return new GridView.builder(
gridDelegate: SliverGridDelegateWithMaxCrossAxisExtent(
maxCrossAxisExtent: 200.0,
childAspectRatio: 0.5),
itemCount: offlineFlashCardList.length,
itemBuilder: (BuildContext context, int index) {
return _getGridItemUI(context, offlineFlashCardList[index]);
});
// return new Center(child: new CircularProgressIndicator());
} else {
debugPrint("Grid ViewBuilder");
return new GridView.builder(
gridDelegate: SliverGridDelegateWithMaxCrossAxisExtent(
maxCrossAxisExtent: 200.0,
childAspectRatio:0.5),
itemCount: flashCardList.length,
itemBuilder: (BuildContext context, int index) {
return _getGridItemUI(context, flashCardList[index]);
});
}
}else {
debugPrint("CircularProgress");
return new Center(child: new CircularProgressIndicator());
}
})
);
}
_getGridItemUI(BuildContext context, FlashCardList item){
return new InkWell(
onTap: () {
_showSnackBar(context, item);
},
child: new Card(
child: new Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
new Image(image: new CachedNetworkImageProvider("https://babymozart.org/babymozartq92C9TLa9UMkulL2m81xHdn9u2R92e1e/image/" + item.image)),
/*new Expanded(
child:new Center(
child: new Column(
children: <Widget>[
new SizedBox(height: 8.0),
new Expanded(
child: AutoSizeText(
item.name, maxLines: 1,
)
)
],
),
)
)*/
],
),
elevation: 2.0,
margin: EdgeInsets.all(5.0),
)
);
}
_showSnackBar(BuildContext context, FlashCardList item){
}
}
答案 0 :(得分:3)
这是一个基于亚历山大答案的示例(因为我发现自己正在寻找如何处理结果的方法):
FutureBuilder(
future: Future.wait([
firstFuture(), // Future<bool> firstFuture() async {...}
secondFuture(),// Future<bool> secondFuture() async {...}
//... More futures
]),
builder: (
context,
// List of booleans(results of all futures above)
AsyncSnapshot<List<bool>> snapshot,
){
// Check hasData once for all futures.
if (!snapshot.hasData) {
return CircularProgressIndicator();
}
// Access first Future's data:
// snapshot.data[0]
// Access second Future's data:
// snapshot.data[1]
return Container();
}
);
答案 1 :(得分:2)
您可以使用Future.wait等待几个Future完成。
body: FutureBuilder<List<FlashCardList>>(
future: Future.wait([
fetchFlashCardList(),
fetchFlashCardListFromDB(),
]),