A way to use a separate activity

[seantheyahn]

Bottom line: you need the Unity player activity initialized in order to call Unity functions from native code. The only way to handle the scenario above would be to have the Unity player activity itself handle the deeplink. Unity will make sure it's initialized prior to the call.

Wrong! You can keep the deeplink call(s) in a queue in the activity, when the engine is loaded you can call an "initialize" method or sth like that from Unity to the activity when the first scene of unity is started, that's when you set a flag indicating that the engine is loaded and is ready to receive messages (so no more need for message queue from this moment), and more importantly, this is where you can send the queued messages to Unity.

I think it is very important not to override the main unity activity, because a lot of plugins are not open source and even if they are, changing their behavior is a hassle and overriding the main unity activity sometimes makes it impossible to use two plugins together. So why not fix it this way and make it portable?