英文:
Flutter, how to return different widget based on future value?
问题
我想要基于一个未来的布尔值，来设置不同的图标传递给列表中的数据卡，我尝试了`.then`或`FutureBuilder`，但仍然没有成功。
Scaffold:
```dart
child: ListView.builder(
itemCount: fullList.length,
itemBuilder: (BuildContext context, int index) {
return dataCard(context, fullList, index);
}),
dataCard:
Row(
children: [
Expanded(
flex: 8,
child: Text(dl[i].Name,
style:
TextStyle(color: Colors.blue[400], fontSize: 16)),
),
Expanded(
flex: 1,
child: setFavouriteIcon(dl[i].ID),
),
],
),
setFavouriteIcon:
Widget setFavouriteIcon(_id) {
final marked = markedFavourites(_id).then((value) { // markedFavourites 返回 Future<bool>
if (value == true) {
return Icon(
size: 24,
Icons.favorite,
color: Colors.red,
);
} else {
return Icon(
size: 24,
Icons.favorite_border_outlined,
color: Colors.red,
);
}
});
return Text(''); // 没有这一行，会出错：必须返回非空值
}
英文:
I would like to base on a future bool value, to set different icons pass back to a data card inside a list, I tried .then or FutureBuilder, but still not successful.
Scaffold:
child: ListView.builder(
itemCount: fullList.length,
itemBuilder: (BuildContext context, int index) {
return dataCard(context, fullList, index);
}),
dataCard:
Row(
children: [
Expanded(
flex: 8,
child: Text(dl[i].Name,
style:
TextStyle(color: Colors.blue[400], fontSize: 16)),
),
Expanded(
flex: 1,
child: setFavouriteIcon(dl[i].ID),
),
],
),
setFavouriteIcon:
Widget setFavouriteIcon(_id) {
final marked = markedFavourites(_id).then((value) { //markedFavourites returns Future<bool>
if (value == true) {
return Icon(
size: 24,
Icons.favorite,
color: Colors.red,
);
} else {
return Icon(
size: 24,
Icons.favorite_border_outlined,
color: Colors.red,
);
}
});
return Text(''); //Without this line, Error: A non-null value must be returned
}}
答案1
得分: 1
您可以在FutureBuilder上包含其他状态。
Widget setFavouriteIcon(_id) {
return FutureBuilder(
future: markedFavourites(_id), // 不应该直接在这里调用方法，特别是在StatefulWidget的情况下
builder: (context, snapshot) {
final value = snapshot.hasData && (snapshot.data as bool? ?? false);
if (value == true) {
return Icon(
size: 24,
Icons.favorite,
color: Colors.red,
);
} else {
return Icon(
size: 24,
Icons.favorite_border_outlined,
color: Colors.red,
);
}
},
);
}
英文:
You can include other state as well on FutureBuilder
Widget setFavouriteIcon(_id) {
return FutureBuilder(
future: markedFavourites(_id),// you shouldn't call method directly here on statefulWidget case
builder: (context, snapshot) {
final value = snapshot.hasData && (snapshot.data as bool? ?? false);
if (value == true) {
return Icon(
size: 24,
Icons.favorite,
color: Colors.red,
);
} else {
return Icon(
size: 24,
Icons.favorite_border_outlined,
color: Colors.red,
);
}
},
);
}
答案2
得分: 0
你应该使用FutureBuilder
class FavoriteWidget extends StatelessWidget {
const FavoriteWidget({super.key});
// 一些未来的值
Future<bool> markedFavorites() async {
// 做一些操作
return true;
// 或者返回false
}
@override
Widget build(BuildContext context) {
return Center(
child: FutureBuilder<bool>(
future: markedFavorites(),
builder: (BuildContext context, AsyncSnapshot<bool> snapshot) {
if (snapshot.hasData) {
if (snapshot.data!) {
return const Icon(
Icons.favorite,
color: Colors.red,
);
}
return const Icon(Icons.favorite_border_outlined);
}
},
),
);
}
}
英文:
you should use FutureBuilder
class FavoriteWidget extends StatelessWidget {
const FavoriteWidget({super.key});
// some future value
Future<bool> markedFavorites() async {
//do smth
return true;
// or return false
}
@override
Widget build(BuildContext context) {
return Center(
child: FutureBuilder<bool>(
future: markedFavorites(),
builder: (BuildContext context, AsyncSnapshot<bool> snapshot) {
if (snapshot.hasData) {
if (snapshot.data!) {
return const Icon(
Icons.favorite,
color: Colors.red,
);
}
return const Icon(Icons.favorite_border_outlined);
}
},
),
);
}
}
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