如何使用 flutter 流从 Firestore 获取数据

Question

StreamBuilder<QuerySnapshot>(
              stream: _fireStore.collection('messages').orderBy('creation',descending: 
                                                                              true).snapshots(),
              // ignore: missing_return
              builder: (context, snapshot) {
                if (!snapshot.hasData) {
                  return Center(
                    child: CircularProgressIndicator(
                      backgroundColor: Colors.lightBlueAccent,
                    ),
                  );
                }
//                print('i have data');
                print(snapshot.data.documents);

print(snapshot.data.documents); is printing null value. 'creation' is a timestamp field added into the fire store.

https://github.com/umakanth-pendyala/Chat-app-with-flutter-and-fire-base is the link to my project in Github. And the code snippet is from the chat_screen page in the lib folder

Answer 1

Try the following:

              builder: (context, snapshot) {
                if (!snapshot.hasData) {
                  return Center(
                    child: CircularProgressIndicator(
                      backgroundColor: Colors.lightBlueAccent,
                    ),
                  );
                }
               else if(snapshot.hasData){             
             print(snapshot.data.documents);
           } 
  return CircularProgressIndicator();

First you need to return a widget, next if you want to print the data then you need to check if the snapshot has data or no. In your code it will always print null since this is asynchronous.

---

After doing the above, also change the query to the following:

_fireStore.collection('messages').orderBy('created',descending: true).snapshots(),

Since you have a field called created in the document and not creation .