Support Flutter add-to-library

[Oklahomawhore]

Use case

Now I have a iOS framework to be used within other apps to integrate account and use center
features. Since we have framework on both iOS and android, I want to use flutter to write some
new pages proposed.

Proposal

Now how add-to-app works is that flutter has to depend on iOS or android Lifecycles if I am correct, so in a iOS framework we have no access to host app's appDelegate or that would be additional work for our framework users. So I wonder is there a solution for that, Thank you very much and wish flutter best and cheer for the flutter team.

[jmagman]

@xster

[xster]

It's a pretty valid use case. I think we'll have to solve the general problem of merging multiple libraries and modularizing the library further first.

Something we can plan for in phase 2+

[xster]

I'm repurposing this to a general add-to-library feature request

[jmagman]

Copying from #35262 (comment) where CocoaPods was specifically mentioned:

If you're willing to use CocoaPods, you could try to use flutter build ios-framework to generate all the Release frameworks you need, then supply them as vendored_frameworks. Of course that means you would need to host those binaries somewhere remotely, as you mentioned, where your users could fetch them by pod 'Your-Framework' in their Podfile.

Once #26712 is done, you would only need to vend the App.framework and any plugins, and your podspec would depend on the exact version of the Flutter pod they were built with.

s.dependency 'Flutter', '1.12.1306'

Pretty much ditto to support Carthage once #24176 is done.