Flutter: The method [] was called on null - firebase

Question

I know this question is asked and answered many times but my problem is a bit different.
I am working with firebase realtime database in flutter. I upload a JSON file in the database for the existing data I have. It looks like this
Each child has 4 properties (Name, Location, Quality, Size)
The children have IDs of 0,1,2.....
When I retrieve this database in my app, it works and it is displayed perfectly.
When I create a new entry from my app, the child has a random ID and it looks like
this.
After that when I try to retrieve the values, the values are printed in the console but on the screen I get:-
The method [] was called on null error. Receiver: null. Tried Calling: []("Name")
.
The Error screen looks like this.
Error in console looks like this
My code for retrieving (I fetch and pass the variable to another screen):-
ref.once().then((DataSnapshot data) {
datatosend = data;
print(datatosend.value);
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => DisplayList(
text: datatosend,
title: CategoryItemsitems[index].name),
));
});
My code for displaying listview:
itemCount: widget.text.value.length,
itemBuilder: (BuildContext context, int index) {
return Padding(
padding: const EdgeInsets.all(8.0),
child: ListTile(
leading: IconButton(
icon: Icon(Icons.edit),
onPressed: () {
print("Edit Pressed!");
}),
title: Text(widget.text.value[index]["Name"]),
subtitle: Text("Quality: " +
widget.text.value[index]["Quality"] +
"\nSize: " +
widget.text.value[index]["Size"] +
"\nLocation: " +
widget.text.value[index]["Location"]),
trailing: IconButton(
icon: Icon(
Icons.delete,
color: Colors.red,
),
onPressed: () {
print("Delete Pressed!");
}),
),
);
}),
My code for creating a new entry:
databaseReference.child(_category).push().set({
"Name": _name,
"Quality": _quality,
"Size": _size,
"Location": _location
}).then((_) {
Scaffold.of(context).showSnackBar(
SnackBar(content: Text('Successfully Added')));
});
Where am I going Wrong?

Answer 1

Hard to know without having access to the code, but this is usually what I do when I run into this type of issues:
run the code in debug mode and put a breaking right after this line:
itemBuilder: (BuildContext context, int index) {. This way you can introspect widget.text.value and see if it's really the array of objects you expected.
otherwise, use a good old print and start printing widget.text.value[index] in your itemBuilder (or even start by printing widget.text, then widget.text.value). You would be surprised how man bugs got figured out with a low-tech print function over the years ;-)
Good luck

Answer 2

After about 10 days, my problem is finally solved.
Some changes I made:
Instead of using, realtime database I am using Cloud Firestore.
Instead of importing the JSON file, I will enter the data manually. Fortunately, it is not very big and earlier also I was writing in the JSON file manually only.
Code to add the data to Firestore. All of this is inside the "onpressed" parameter of a button. All the inputs are taken by a simple form.
firestoreInstance.collection("cars").add({
"Name": _name,
"Quality": _quality,
"Size": _size,
"Location": _location,
}).then((value) {
print("Added Successfully")});
For fetching the data and access its different fields I am using a stream-builder:
StreamBuilder(
stream: Firestore.instance
.collection("cars")
.orderBy("Name") //To display the list by Name
.snapshots(),
builder: (context, snapshot) {
if (!snapshot.hasData) {
return Center(child: CircularProgressIndicator());
}
else {
if(snapshot.data.documents.length>0)
{
return ListView.builder(
itemCount: snapshot.data.documents.length, //no. of entries fetched
itemBuilder: (BuildContext context, int index) {
return ListTile(
title: Text(
snapshot.data.documents[index].data()["Name"]), //Accessing the Name property
subtitle: Text("Quality: " +snapshot.data.documents[index].data()["Quality"] + //Accessing the Quality property
"\nSize: " +snapshot.data.documents[index].data()["Size"] + //Accessing the Size property
"\nLocation: " +snapshot.data.documents[index].data()["Location"]) //Accessing the Location property
);
}
)}
}
}
}
)
I apologize if some of the closing parenthesis does not match. I pulled these important snippets from my very messy code.