在 Flutter / Dart 和 Sound Null 中检索 firebase firestore 文档

Question

I am working my way through a Udemy Flutter class and I am in a chapter dealing with Firebase. The class is about 3-4 years old and it seems is just old enough that the sample completed code crashes when accessing the Firebase portions. I started a new project from scratch and cobbled bits and pieces to get it mostly up and running but I have now hit a dead end. The new project and the firebase plugins are Sound Null and the class code is not. Getting and printing data from the database worked fine until I tried getting it hooked up to a stream. I am specifically running into a problem iterating over the received documents. When I set up the message variable using (the Flutter) snapshot.data in a for-in loop and try to iterate over the returned documents (#1) I have a null problem. Without specifying the type (#1a) as AsyncSnapshot the for-in loop errors that I cannot iterate over a non nullable. Changing the type gets rid of the compile time error but generates a runtime error of "type _JsonQuerrySnapshot is not a subtype of type Iterable". Dart is not my primary language and I have been pulling my hair out googling this for several hours to no avail. Any help is appreciated.

final _firestore = FirebaseFirestore.instance; //<-----earlier in the code

      children: <Widget>[

        StreamBuilder<QuerySnapshot>(
          stream: _firestore.collection('messages').snapshots(),
          builder: (BuildContext context, AsyncSnapshot<dynamic> snapshot) { //<----Problem #1a here
            List<Text> messageWidgets = [];
            if (snapshot.hasData) {

              final messages = snapshot.data;

              for (var message in messages) { //<----------Problem #1 here
                final messageText = message.data['text'];
                final messageSender = message.data['sender'];
                final messageWidget =
                    Text('$messageText from $messageSender');
                messageWidgets.add(messageWidget);
              }
            }
            return Column(
              children: messageWidgets,
            );
          },
      

Answer 1

Well, after another hour or so of googling around I found the right place to look. The docs for the flutter plugin for firestore have a massive difference from the course I am taking. Reading(ctrl-c, ctrl-v) them I'm at least able to mostly understand and have the program back on track to finish my course.