[firebase_messaging] Android: background service refactoring

[ened]

Description

Currently, the FM plugin register 2 method channels (for FG and BG processing).
This breaks when a App consists of more than 1 standard isolate, as it means on every isolate instantiation, the plugin will overwrite the previous background channel.

By setting the background channel within the plugin registration, it also introduced a memory leak (see #260). More importantly, when the foreground App is stopped, notifications may not always come through, as the background channel has been overwritten.

Update 2020/06/07:
The PR has been updated since and now uses a FlutterEngine object internally which removes most of the previously needed integration work on Android. The need to register a plugin registrant callback has been removed.
Additionally, analysis with LeakCanary has been done and memory leaks removed.

Related Issues

This PR is based on #259; Merging that first is preferred to declutter this PR a bit.

#260

Checklist

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• I updated CHANGELOG.md to add a description of the change.
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Breaking Change

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• Yes, this is a breaking change (please indicate a breaking change in CHANGELOG.md and increment major revision).
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/cc @kroikie

[nhwilly]

On behalf of those of us that don't have the skills to troubleshoot at this level, a sincere thanks.

Great to see these problems identified and addressed in rapid succession.

[ened]

/cc @bparrishMines

[goody-h]

Glad to see this is a work in progress

[heaather]

Yes

…

On Thu, Nov 14, 2019, 6:21 AM Goodhope Ordu ***@***.***> wrote: Glad to see this is a work in progress — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#261>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ANTZ3JNKX5LR2ASWEZIL3N3QTUYEBANCNFSM4I5EL6HA> .

[ened]

The PR has been refactored and includes a few more simplifications on the Android side, including:

• Remove the need to register things in the host application by switching to a FlutterEngine internally
• Remove all static variables, so that the host Activity won't leak
• Remove further variables as needed

I'd appreciate if the community could help and test this PR.

If you are interested, please adjust the dependency_overrides field in your pubspec.yaml and add the following:

  firebase_messaging:
    git:
      url: https://github.com/ened/flutterfire.git
      path: packages/firebase_messaging
      ref: 254e43d18ba0862d9406fa0d872689d1961b3025

[ened]

@invertase - similarly, this PR could use someones attention. We are using it in production as else wise we'd run into memory leaks or similar. Also, it simplifies the integration on App side quite significantly.

[Salakar]

Thanks for this PR, its on our radar don't worry 🙃 we're close to shipping Functions & Storage reworks, after which we're focusing on messaging

[Salakar]

Also if you have any other PRs or issues that you're tracking and think we should look at please let us know below, thanks