Add support for checking for versions

[felix-barz-brickmakers]

It would be awesome if the library could also support a basic update check, using the "standard" APIs, i.e. google play and the iTunes store. To support this, the following would have to be done.

• use https://pub.dev/packages/package_info to get the version name/code
• use the version code provided by in_app_update for android
• use the itunes API to get the newest ios version (See https://pub.dev/packages/upgrader#itunes-search-api for a package that can do that)
• provide a checkForUpdates method (or similar), something like the following:

  
  enum UpdateLevel { skip, optional, required }

NativeUpdater.checkForUpdates( BuildContext context, { UpdateLevel Function(int, int) androidCompareVersion, // compare version code aka. build number UpdateLevel Function(String, String) iosCompareVersion, // compare version string // other parameters from displayUpdateAlert, except forceUpdate, which is replaced by the UpdateLevel result });

We need two methods for comparing, because on android, the version code / build number is used by google play, while on iOS the actual public version string is used.

[milhomem]

Hi, @felix-barz-brickmakers, I see your point but this is out of the scope proposed by this library.

We believe that it's up to the developer to decide when or how to define when the update is needed. Not always you want to update the app as soon a new version is available. Some might want to control this via API or by some business rule that gives their users the best experience with less disruption.

Although I understand that some might want to use the app versions to trigger updates, this is already provided by the platforms natively.

We would happily accept this second helper entrypoint if you/someone can provide a PR for it, but it's not something you should expect us to work on.