We want to develop mobile keyboard app - (Third party keyboard) that have some unique features (such translate on the keyboard).
We would like to know if there is a way to developed it once both for IOS and Android, with Flutter, or any other solution?
There's a long and a short answer to this. The short answer is basically no, it's not feasible at this time to do this.
The long answer is that it may be somewhat possible but with a fairly large amount of work for you to do. You're going to have to first create and appropriate project type in android and ios, and then import the dart code & set up the build. You may be able to start with a normal flutter application and modify the xcode/gradle builds to match the specifics for ios/android, but I'd guess that's somewhat unlikely. So you'll probably still have to maintain two separate projects, but which could import the same dart library for the UI.
Because Android and iOS use different APIs for their keyboards, you're going to need to write a Platform Plugin or at least method channels which communicate between your app and the native code, for each of iOS and Android. You'll also probably have to embed the flutter view yourself - see this example as I'd bet the normal FlutterApplication etc won't apply.
I'd guess that on android you could probably get this to work eventually with a lot of work (depending on how familiar you are with android, platform channels, and integrating libraries such as flutter's into the build); on iOS you might have luck but it's somewhat conceivable that iOS blocks certain features that flutter needs in the keyboard for performance or security reasons - just guessing from my experiences developing apps in native iOS although I haven't done a keyboard specifically.
That being said, if you do try this I'd be interested to hear the results, and if you were to go about it in a somewhat generic way that could be re-used it would be of great benefit to the flutter community!
