My goal is that I want to customise my own Android phone to automatically forward text messages from user defined phone numbers onto other user defined phone numbers. I tried updating a very simple app to do this:
However I found that once I had updated to newer Android versions, the app started up and allowed me to set a forwarding number, but did not actually forward the SMS (I used my phone in USB debugger mode). The SMSReceiver class did not get the message that an SMS had arrived I found when I debugged it. I read more, and it seems that only the default SMS app is allowed to have anything to do with text messages. So now, I want to start from the source code of the stock/default SMS app that comes with Android so that I can add the features I am interested in to it.
I'm open to different approaches, but I don't want to download a crapware app with ads or pay nagging.
Doing a little more research, I found that Signal can handle SMS messages, but it seems like quite a big and complicated app.
Any advice appreciated!