Does streambuilder flutter uses cache?-CodePudding

I'm working on a streambuilder in flutter and this one as the stream the FirebaseAuth.instance.authStateChanges(). I do have a question because I saw that the information is saved but I want to know more about it, as I don't know why if the app is closed and reopened the data is still there. How is the data saved in the StreamBuilder? I found it usefull but I need to understand what is going on image

Thank you

CodePudding user response：

The StreamBuilder widget in Flutter does not use any kind of caching by default, regardless of whether it is used with Firebase or not. Each time a new Stream is provided to the StreamBuilder, it will start listening to the stream and build the widget tree based on the current data emitted by the stream.

However, you can easily implement caching behavior in your StreamBuilder by using the StreamTransformer class to transform the stream before passing it to the StreamBuilder. For example, you could use a StreamTransformer to cache the latest data emitted by the stream and then emit that data to the StreamBuilder whenever a new listener is added. This would give the appearance of the StreamBuilder using a cache, even though it is actually just transforming the stream in a particular way.

Here's an example of how you could use a StreamTransformer to implement caching behavior in a StreamBuilder when using Firebase:

StreamBuilder(
  stream: FirebaseDatabase.instance
      .reference()
      .child("my_data")
      // Transform the stream to cache the latest data
      .transform(
        StreamTransformer.fromHandlers(
          handleData: (data, sink) {
            // Save the latest data emitted by the stream
            _latestData = data;
          },
          handleError: (error, stackTrace, sink) {
            // Handle errors in the stream
            sink.addError(error, stackTrace);
          },
        ),
      ),
  builder: (context, snapshot) {
    // Build the widget tree based on the data emitted by the stream
  },
)

In this example, the StreamTransformer is used to cache the latest data emitted by the Firebase database reference, and then emit that data to the StreamBuilder whenever a new listener is added. This allows the StreamBuilder to show the latest data without having to wait for the data to be updated in the Firebase database.

CodePudding user response：

StreamBuilder not caching anything, instead Firebase SDK caching its own state for you automatically.

the documentation :

The Firebase SDKs for all platforms provide out of the box support for ensuring that your user's authentication state is persisted across app restarts or page reloads.

On native platforms such as Android & iOS, this behavior is not configurable and the user's authentication state will be persisted on device between app restarts. The user can clear the apps cached data using the device settings, which will wipe any existing state being stored.

remember this line first time before app running?

await Firebase.initializeApp(options: DefaultFirebaseOptions.currentPlatform);

you are basically run all firebase core before your own app run, the magic happen there. its not configurable based on the doc.

however on web, there is different case where you can configure based on session or locally instead of IndexedDB

source