How to get data from the firebase and store it into a list for futher manipulation in dart

Question

List<DocumentSnapshot> docs = snapshot.data.docs; _selectedSubjects = docs .map( (doc) => Subject( doc['SubjectName'].data(), doc['courseIcon'].data(), doc['courseCode'].data(), ), ) .toList();

I have a class called subject that has attributes/members courseCode, courseIcon, and lastly subjectName. Everything is okay so far, but vs code is saying:

Type: dynamic

The property 'docs' 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 ('!')."

I have already imported all the necessary libraries, as well as vs code's reccomendations. What should I try?

Frank van Puffelen · Accepted Answer · 2022-12-26 19:53:18Z

The error means that snapshot.data may be null, so you need to first verify that it's not null before you can assign it to your non-nullable docs variable:

var querySnapshot = snapshot.data; if (querySnapshot != null) { List<DocumentSnapshot> docs = querySnapshot.docs; _selectedSubjects = docs .map( (doc) => Subject( doc['SubjectName'], doc['courseIcon'], doc['courseCode'], ), ) .toList(); }

The local querySnapshot variable is guaranteed to be non-null inside the if block, so now you can simply assign querySnapshot.docs to docs.

I also removed the .data() calls, as @Gwhyyy pointed out in their comment.

You might want to take a moment to read up on nullability in Dart as you're likely to encounter many more situations where the type changes based on handling null.

I guess there is another error in trying to get fields as this doc['SubjectName'].data()
I have followed your instructions and thanks for the link on nullability in Dart. I did learn a lot. However I am still getting an error. A different one this time around "Type: dynamic The getter 'docs' isn't defined for the type 'Object'. Try importing the library that defines 'docs', correcting the name to the name of an existing getter, or defining a getter or field named 'docs'."
Never mind I have fixed the new error got help from an answer on stack overflow.

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