Android Question How to start a second app and pass/return parameter ?


Licensed User
I have an app without a UI that runs as a background service
When he receives an sms with a specific command he has to start a second app and pass it commands (text strings)
The second app, which has a user interface, when closed by the operator must return information (text strings) to the starting service
How to pass parameters from the service to the second app?
And to return information from the second app to the service, when the second app is closed?
Is there any code snippets to achieve the above?