[in_app_purchase] Federated Android implementation

[mvanbeusekom]

This PR adds the Android implementation of the new "in_app_purchase_platform_interface" (see PR #3781).

Note: when running Flutter commands for the in_app_purchase_android package I keep getting the warning below. I think this is caused by the fact that the in_app_purchase_android is missing a MainActivity.java (since is contains pure plugin code and no example which will be part of the in_app_purchase package), but I am not sure. If I made a configuration mistake I would be happy to fix it.

Warning:

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
Warning
──────────────────────────────────────────────────────────────────────────────
Your Flutter application is created using an older version of the Android
embedding. It's being deprecated in favor of Android embedding v2. Follow the
steps at

https://flutter.dev/go/android-project-migration

to migrate your project.
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

If you had to change anything in the flutter/tests repo, include a link to the migration guide as per the breaking change policy.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the Flutter Style Guide and the C++, Objective-C, Java style guides. (Note that unlike the flutter/flutter repo, the flutter/plugins repo does use dart format. See plugin_tool format)
• I signed the CLA.
• The title of the PR starts with the name of the plugin surrounded by square brackets, e.g. [shared_preferences]
• I listed at least one issue that this PR fixes in the description above.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy.
• I updated CHANGELOG.md to add a description of the change.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making or feature I am adding, or Hixie said the PR is test exempt.
• All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel on Discord.

[google-cla]

☹️ Sorry, but only Googlers may change the label cla: yes.

[google-cla]

☹️ Sorry, but only Googlers may change the label cla: yes.

[cyanglaz]

since is contains pure plugin code and no example which will be part of the in_app_purchase package

I think we should add examples for this plugin as well, also have a readme to document well how to use only android implementations if people want to (since we advertised it in our readme already)

We should also do the same for the iOS package.

However, these are not priorities since most of the people will use the unified API. But still, I think this can be on our future roadmap. We should create an issue and add TODOs to track it.

I created the issue: flutter/flutter#81695, do you mind adding TODO in this PR?

[cyanglaz]

Is this android only? Does it make sense to be in the platform_interface?

[mvanbeusekom]

At the moment it is only used in the Android package. On iOS we don't need this specific exception. However I can imagine the exception to be useful on other platforms in the future.

So I wasn't sure to add it now to the platform_interface or later if we really need it on multiple platform (by that time we might have forgotten that there is a similar class in the Android implementation).

[cyanglaz]

Yes, I think it belongs to the platform_interface

[mvanbeusekom]

I created a separate PR (#3852) which adds the InAppPurchaseException to the platform_interface. Once that is merged I will make sure it gets removed from this PR.

[mvanbeusekom]

since is contains pure plugin code and no example which will be part of the in_app_purchase package

I think we should add examples for this plugin as well, also have a readme to document well how to use only android implementations if people want to (since we advertised it in our readme already)

We should also do the same for the iOS package.

However, these are not priorities since most of the people will use the unified API. But still, I think this can be on our future roadmap. We should create an issue and add TODOs to track it.

I created the issue: flutter/flutter#81695, do you mind adding TODO in this PR?

No problem at all, but I am not sure where I would add these TODOs (as in which files)? Since there is no example, where would it make the most sense to add a TODO so we encounter it in the future?

[cyanglaz]

since is contains pure plugin code and no example which will be part of the in_app_purchase package

I think we should add examples for this plugin as well, also have a readme to document well how to use only android implementations if people want to (since we advertised it in our readme already)
We should also do the same for the iOS package.
However, these are not priorities since most of the people will use the unified API. But still, I think this can be on our future roadmap. We should create an issue and add TODOs to track it.
I created the issue: flutter/flutter#81695, do you mind adding TODO in this PR?

No problem at all, but I am not sure where I would add these TODOs (as in which files)? Since there is no example, where would it make the most sense to add a TODO so we encounter it in the future?

In the README.md, we can add todo saying we need to add example apps.

[cyanglaz]

Yes, I think it belongs to the platform_interface

[mvanbeusekom]

In the README.md, we can add todo saying we need to add example apps.

Done. I also added a similar comment to the in_app_purchase_ios README.md file as part of PR #3851.

[cyanglaz]

LGTM