在 Flutter 上读取从 Firebase 更改的值

Question

I want to read and display values from my Firebase realtime database on flutter. I have managed to read and display a value from my database, but it won't get updated on my app when it's changed. I think I have to use onValue(), but I can't get it working using it.

I am using a future builder to display the data on my app, would I need it using onValue()?

Future getVolumesFirst() async {
  final ref = FirebaseDatabase.instance.ref();
  final snapshot = await  ref.child('path').get();
  if (snapshot.exists) {
    print(snapshot.value);
    return snapshot.value;
  } else {
    print('No data available.');
  }
}

Answer 1

When you call get() you indeed get the value only once, and it doesn't monitor for updates. The Firebase documentation contains a pretty good example of listening for updates :

DatabaseReference starCountRef =
        FirebaseDatabase.instance.ref('posts/$postId/starCount');
starCountRef.onValue.listen((DatabaseEvent event) {
    final data = event.snapshot.value;
    updateStarCount(data);
});

Alternatively, you can just use onValue (without listen ) and use that value in a StreamBuilder .

Also see:

• other questions about using onValue
• questions about using onValue with a StreamBuilder