当屏幕加载时，我希望初始化状态使用通过有状态窗口小部件传递的Future 填充列表。但是，从将来开始，我的方法将崩溃并且不起作用。
我的代码
@override
void initState() async {
FutureBuilder(
future: widget.imageList,
builder: (context, snapshot) {
switch (snapshot.connectionState) {
case ConnectionState.none:
print('NONE');
break;
case ConnectionState.active:
case ConnectionState.waiting:
print("WAITING");
break;
case ConnectionState.done:
print("DONE");
setState(() {
imgList = widget.imageList as List<String>;
});
break;
}
},
);
super.initState();
}
产生错误
════════ Exception caught by widgets library ═══════════════════════════════════
_BottomSheetWidgetState.initState() returned a Future.
The relevant error-causing widget was
MaterialApp
状态小部件，列表通过该小部件
List<String> imgList = List<String>();
class BottomSheetWidget extends StatefulWidget {
BottomSheetWidget({Key key, this.name, this.imageList}) : super(key: key);
String name;
Future<List<String>> imageList;
整个编辑的代码：
List<String> imgList = List<String>();
class BottomSheetWidget extends StatefulWidget {
BottomSheetWidget({Key key, this.name, this.imageList}) : super(key: key);
String name;
Future<List<String>> imageList;
@override
_BottomSheetWidgetState createState() => _BottomSheetWidgetState();
}
class _BottomSheetWidgetState extends State<BottomSheetWidget> {
int _current = 0;
final List<Widget> imageSliders = imgList
.map((item) => Container(
child: Container(
margin: EdgeInsets.all(5.0),
child: ClipRRect(
borderRadius: BorderRadius.all(Radius.circular(5.0)),
child: Stack(
children: <Widget>[
Image.network(item,
fit: BoxFit.cover, height: 1000.0, width: 1000.0),
Positioned(
bottom: 0.0,
left: 0.0,
right: 0.0,
child: Container(
decoration: BoxDecoration(
gradient: LinearGradient(
colors: [
Color.fromARGB(200, 0, 0, 0),
Color.fromARGB(0, 0, 0, 0)
],
begin: Alignment.bottomCenter,
end: Alignment.topCenter,
),
),
),
),
],
)),
),
))
.toList();
@override
Widget build(BuildContext context) {
return FutureBuilder(
future: widget.imageList,
builder: (context, snapshot) {
switch (snapshot.connectionState) {
case ConnectionState.none:
print('NONE');
break;
case ConnectionState.active:
case ConnectionState.waiting:
print("WAITING");
break;
case ConnectionState.done:
print("DONNE");
setState(() async {
imgList = snapshot.data as List<String>;
});
return Container(
decoration: BoxDecoration(
color: Colors.red,
borderRadius: BorderRadius.circular(25),
),
height: MediaQuery.of(context).size.height * 0.85,
width: MediaQuery.of(context).size.width,
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
mainAxisSize: MainAxisSize.max,
children: <Widget>[
Padding(
padding: EdgeInsets.symmetric(horizontal: 15),
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
mainAxisAlignment: MainAxisAlignment.end,
children: <Widget>[
CarouselSlider(
items: imageSliders,
options: CarouselOptions(
enlargeCenterPage: true,
enlargeStrategy: CenterPageEnlargeStrategy.height,
height: MediaQuery.of(context).size.height - 500,
aspectRatio: 2.0,
onPageChanged: (index, reason) {
setState(() {
_current = index;
});
}),
),
Row(
mainAxisAlignment: MainAxisAlignment.center,
children: imgList.map((url) {
int index = imgList.indexOf(url);
return Container(
width: 8.0,
height: 8.0,
margin: EdgeInsets.symmetric(
vertical: 10.0, horizontal: 2.0),
decoration: BoxDecoration(
shape: BoxShape.circle,
color: _current == index
? Color.fromRGBO(0, 0, 0, 0.9)
: Color.fromRGBO(0, 0, 0, 0.4),
),
);
}).toList(),
),
Text(widget.name,
style: TextStyle(
fontSize: 30,
color: Colors.white,
fontWeight: FontWeight.bold)),
Text("United Kingdom",
style: TextStyle(
fontSize: 18,
color: Colors.white,
)),
],
),
)
],
),
);
break;
}
},
);
}
}
控制台出现新错误：
flutter: WAITING
════════ Exception caught by widgets library ═══════════════════════════════════
A build function returned null.
The relevant error-causing widget was
FutureBuilder<List<String>>
lib/common_widget/bottom_sheet.dart:54
════════════════════════════════════════════════════════════════════════════════
flutter: DONNE
════════ Exception caught by widgets library ═══════════════════════════════════
setState() callback argument returned a Future.
The relevant error-causing widget was
FutureBuilder<List<String>>
lib/common_widget/bottom_sheet.dart:54
════════════════════════════════════════════════════════════════════════════════
答案 0 :(得分：1)
initState方法在设计上是同步的。您可以在覆盖的FutureBuilder方法中返回initState小部件，而不是在FutureBuilder方法中创建build小部件。随时查看FutureBuilder小部件here的文档，以获取有关其工作方式的示例。
似乎setState回调函数中的代码也有问题。您可能想将imgList = widget.imageList as List<String>;替换为imgList = snapshot.data as List<String>;，以便使用已完成的将来的数据。
在所有情况下，build方法似乎都没有返回窗口小部件也存在问题。我已经获取了更新的代码示例，并进行了如下修改：
import 'package:flutter/material.dart';
class BottomSheetWidget extends StatefulWidget {
BottomSheetWidget({Key key, this.name, this.imageList}) : super(key: key);
final String name;
final Future<List<String>> imageList;
@override
_BottomSheetWidgetState createState() => _BottomSheetWidgetState();
}
class _BottomSheetWidgetState extends State<BottomSheetWidget> {
int _current = 0;
@override
Widget build(BuildContext context) {
return FutureBuilder<List<String>>(
future: widget.imageList,
builder: (context, snapshot) {
if (snapshot.connectionState == ConnectionState.done) {
final imgList = snapshot.data;
return Container(
decoration: BoxDecoration(
color: Colors.red,
borderRadius: BorderRadius.circular(25),
),
height: MediaQuery.of(context).size.height * 0.85,
width: MediaQuery.of(context).size.width,
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
mainAxisSize: MainAxisSize.max,
children: <Widget>[
Padding(
padding: EdgeInsets.symmetric(horizontal: 15),
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
mainAxisAlignment: MainAxisAlignment.end,
children: <Widget>[
CarouselSlider(
items: imgList.map(
(item) {
return Container(
child: Container(
margin: EdgeInsets.all(5.0),
child: ClipRRect(
borderRadius:
BorderRadius.all(Radius.circular(5.0)),
child: Stack(
children: <Widget>[
Image.network(
item,
fit: BoxFit.cover,
height: 1000.0,
width: 1000.0,
),
Positioned(
bottom: 0.0,
left: 0.0,
right: 0.0,
child: Container(
decoration: BoxDecoration(
gradient: LinearGradient(
colors: [
Color.fromARGB(200, 0, 0, 0),
Color.fromARGB(0, 0, 0, 0)
],
begin: Alignment.bottomCenter,
end: Alignment.topCenter,
),
),
),
),
],
),
),
),
);
},
).toList(),
options: CarouselOptions(
enlargeCenterPage: true,
enlargeStrategy: CenterPageEnlargeStrategy.height,
height: MediaQuery.of(context).size.height - 500,
aspectRatio: 2.0,
onPageChanged: (index, reason) {
setState(() {
_current = index;
});
},
),
),
Row(
mainAxisAlignment: MainAxisAlignment.center,
children: imgList.map((url) {
return Container(
width: 8.0,
height: 8.0,
margin: EdgeInsets.symmetric(
vertical: 10.0, horizontal: 2.0),
decoration: BoxDecoration(
shape: BoxShape.circle,
color: _current == imgList.indexOf(url)
? Color.fromRGBO(0, 0, 0, 0.9)
: Color.fromRGBO(0, 0, 0, 0.4),
),
);
}).toList(),
),
Text(
widget.name,
style: TextStyle(
fontSize: 30,
color: Colors.white,
fontWeight: FontWeight.bold,
),
),
Text(
"United Kingdom",
style: TextStyle(
fontSize: 18,
color: Colors.white,
),
),
],
),
)
],
),
);
} else {
return CircularProgressIndicator();
}
},
);
}
}