I want to get data from firebase and an error has occurred.

this is the code :

  late final dref = FirebaseDatabase.instance.reference();
  late DatabaseReference databaseReference;
  showData(){
    dref.once().then((snapshot){
      print(snapshot.snapshot.value);
    });
  }

@override
void initState(){ 
  super.initState();
  databaseReference = dref;
}

child: 
                Container(  
                  height:300,
                  child: GridView.count(
                    crossAxisCount: 2, 
                    crossAxisSpacing: 12, 
                    mainAxisSpacing: 8,
                    childAspectRatio: 1.30,
                    children: [
                      FirebaseAnimatedList(
                        shrinkWrap:true,
                        query: databaseReference,
                      itemBuilder: ( BuildContext context, DataSnapshot snapshot, Animation animation, int index){  
                        return ListTile(
                          title: Text(snapshot.value!["intime"]),
                          subtitle : _parkingslot(name:'Floor'),);
                      }),

it has an error. That '[' got a red underline and the sentence is : Returns the contents of this data snapshot as native types. 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 ('!').

I've tried to add '!' and '?.' but still got an error, but the sentence is : The operator '[]' isn't defined for the type 'Object'.

please help

CodePudding user response：

There is no guarantee that snapshot.value is a Map, since it is declared as returning an Object?. If you know for certain that it returns a map, you'll have to tell the compiler about that by casting the result:

itemBuilder: ( BuildContext context, DataSnapshot snapshot, Animation animation, int index){  
  var map = Map<String, dynamic>.from(snapshot.value! as Map; //