Can't get around these errors in flutter cause of null safety-CodePudding

itemCount: snapShot.data.length, error - The property 'length' can't be unconditionally accessed because the receiver can be 'null'. Try making the access conditional (using '?.') or adding a null check to the target ('!').

DocumentSnapshot sliderImage = snapShot.data[index]; error -The method '[]' can't be unconditionally invoked because the receiver can be 'null'. Try making the call conditional (using '?.') or adding a null check to the target ('!').

Map getImage = sliderImage.data();

error - A value of type 'Object?' can't be assigned to a variable of type 'Map<dynamic, dynamic>'. Try changing the type of the variable, or casting the right-hand type to 'Map<dynamic, dynamic>'

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:flutter/material.dart';

class ImageSlider extends StatefulWidget {
const ImageSlider({Key? key}) : super(key: key);

@override
_ImageSliderState createState() => _ImageSliderState();
}

class _ImageSliderState extends State<ImageSlider> {
Future getSliderImageFromDb() async {
var _fireStore = FirebaseFirestore.instance;
QuerySnapshot snapshot = await _fireStore.collection('slider').get();
return snapshot.docs;
}

@override
void initState() {
getSliderImageFromDb();
super.initState();
}

@override
Widget build(BuildContext context) {
 return Column(
  children: [
    FutureBuilder(
      initialData: [], //remove later
      future: getSliderImageFromDb(),
      builder: (_, snapshot) {
        return snapshot.data == null
            ? Container()
            : CarouselSlider.builder(
                itemCount:
                    snapshot.data!.length,
                  itemBuilder: (context, int index, int pageIndex) {
                  DocumentSnapshot sliderImage = 
                  snapshot.data[index];
                  Map getImage = sliderImage.data();
                  return Image.network(getImage['image']);
                },
                options: CarouselOptions());
      },
    )
  ],
);
}
}

CodePudding user response：

You also need to specify the FutureBuilder generic type Like let's say if you have got a list of user models from DB then it should be

 FutureBuilder<List<UserModel>>(
  initialData: [],
  future: getSliderImageFromDb(),
  builder: (_, List<UserModel> snapshot) {
    return Container();
  },
);

In Flutter2, If it is a nullable then you need to handle it, like lets say if a list is like

List<UserModel?>? users; // as this might me nullable

Then it returns a nullable UserModel, So if you want to assign this to non-nullable fields then you need to handle

final String userName = users?.elementAtIndex(3)?.userName ?? 'N.A';

Or, If you are sure that it's not a null then you can

final String userName = users!.elementAtIndex(3)!.userName;

But if its a null it throws an exception.

CodePudding user response：

snapshot.data.length

Here snapShot.data may be null so null safety is complaining.So you make sure its never null by null checking like this

if(snapshot.data==null)
 return "Something Else"

then ensure the null safety that its value will not be null ever by

snapshot.data!.length