(WIP) Predictive back OpenContainer transition

[justinmc]

Flutter now partially supports predictive back on Android, meaning that a back gesture is able to "peek" behind the current route or the app itself to see where the back gesture will go. This should work for open container transitions too, where a back gesture starts to peek, and releasing transitions the route into its "closed" anchor in the previous route. This PR attempts to add support to this to the existing open container transition in this package.

Part of flutter/flutter#131961

Depends on:
flutter/flutter#141373
flutter/engine#49093

[bebaoboy]

Hello, I don't know if it's appropriate to leave a non-work-related comment here but I just wanna say that I'm very excited and looking forward to you guys work on integrating Predictive Back into flutter, especially this WIP. I just started flutter for some weeks and got hooked with flutter animation and recently, predictive gesture animation. Then upon finding out about the fact that it will be put into Open Container I was so amazed and impressed. That's a lotta work😆

May I ask you this question: Can you estimate when the stable channel will get this feature? Or can I at least try it somehow on some flutter beta channel? Not sure if I can have multiple version of flutter on my windows because I need to keep the stable version (as of the project I'm doing).

Anyways have a great day, thanks for reading my comment! I got to go, still got a bunch of flutter to learn more!!!

[justinmc]

@bebaoboy Thanks so much for the encouragement! Credit to @maRci002 for taking the initiative on the built-in route transitions.

Those built-in transitions (flutter/flutter#141373 and flutter/engine#49093) have already been cut into the upcoming stable release, but for these open container transitions I'm not sure exactly how the release process works. If you are able to install the latest version of animations, even if you're using Flutter's stable channel, I think you'll be able to use these transitions once this PR is merged. There should not be any further framework changes needed for this to work.

I'm hoping to get back to finishing this PR soon.

[bebaoboy]

Hello, that's amazing to here! Thank you for your contributing to Flutter and making it better everyday.
And by the way, do you happen to know when the next release of stable channel will be? I will need to wait until then to be able to use Predictive Back Gesture on Flutter, right?
And do I need to install like the beta/dev version of the package animations (after this Open Container PR got merged)?

[justinmc]

Unfortunately I'm not sure about the release processes or timeline. I think that there are no release channels for these individual packages, so the next release after this PR is merged will have it.