Background monitoring on Android

[Lukasz Piliszczuk]

Users implementing background monitoring are required to subclass FlutterApplication on the Android side:

class App : FlutterApplication() {

    override fun onCreate() {
        super.onCreate()

        BeaconsPlugin.init(this, object : BeaconsPlugin.BackgroundMonitoringCallback {
            override fun onBackgroundMonitoringEvent(event: BackgroundMonitoringEvent): Boolean {
                // callback when a monitoring event is detected in background
                // start flutter activity, or do something else custom in java/kotlin
                val intent = Intent(this@App, MainActivity::class.java)
                startActivity(intent)
                return true
            }
        })
    }
}

Once alarm_manager is fixed (flutter/flutter#17566), this library will expose a similar API: a callback purely written in Dart on the Flutter side.