Flutter 'map' Dynamic call of null. Receiver: Instance of '_Future<dynamic>' Arguments: [Instance of '(dynamic) => Builder'] - list

Question

i am trying to make a banner using this list which can be accessed with function "getBannerList" instead of having to manually write a list in this carousel
if i set items by manually putting a list at items: ['base64string','base64string','base64string'].map it will work fine but when i replace it with the function it causes this error
Error
The following NoSuchMethodError was thrown building MyApp(dirty, dependencies: [MediaQuery], state: _MyAppState#5a46f):
'map'
Dynamic call of null.
Receiver: Instance of '_Future<dynamic>'
Arguments: [Instance of '(dynamic) => Builder']
Code for carousel
Dependencies: carousel_slider: ^4.0.0
CarouselSlider(
options: CarouselOptions(
height: MediaQuery.of(context).size.height * 0.15,
autoPlay: true,
autoPlayInterval: Duration(seconds: 5),
initialPage: 0,
),
items: getBannerList().map((e) { // <---- if i replaced this with ['asdf','asdf,'asdf].map((e) it works fine
return Builder(
builder: (BuildContext context) {
return Container(
width: MediaQuery.of(context).size.width,
margin: EdgeInsets.symmetric(horizontal: 5.0),
decoration: BoxDecoration(
image: DecorationImage(image: MemoryImage(base64Decode(e.toString()))),
color: Colors.white,
),
);
},
);
}).toList(),
),
GetList Function
getBannerList() async{
dynamic data = await getDashBoardBannerData();
print(data);
return data;
}
returns (example of return cause base64 string is too long):
['base64imgstring','base64imgstring','base64imgstring']

Answer 1

getBannerList method returns Future<dynamic> not List :
1- change method signature to Future<List<String>> getBannerList() async{}
2- define a variable in your StatefullWidget called
late final Future<List> bannerList;
3- initialize you variable in init state
#override
void initState(){
bannerList = getBannerList();
}
4- now we should use FutureBuilder with our basserList
FutureBuilder<List<String>>(
future: bannerList, // your future data
builder: (BuildContext context, AsyncSnapshot<List<String>> snapshot) {
if (snapshot.hasData) {
return CarouselSlider(
options: CarouselOptions(
height: MediaQuery.of(context).size.height * 0.15,
autoPlay: true,
autoPlayInterval: Duration(seconds: 5),
initialPage: 0,
),
items: snapshot.data.map((e) {
return Builder(
builder: (BuildContext context) {
return Container(
width: MediaQuery.of(context).size.width,
margin: EdgeInsets.symmetric(horizontal: 5.0),
decoration: BoxDecoration(
image: DecorationImage(image: MemoryImage(base64Decode(e.toString()))),
color: Colors.white,
),
);
},
);
}).toList(),
);
} else if (snapshot.hasError) {
return Text('Loading Error'); // error state
} else {
return CircularProgressIndicator(); // loading state
},
you should use explicit types for fewer bugs.