Create an app to access and external exported activity

[vellangelus]

Hi! I am new in Android development, I would like to ask how would be the code for an app "A" with a button to call an activity from another app "B" that is exported. If this activity give you access to sdcard files, how can I download those files or modify those files from the app "A". This would be for hacking demonstration purposes

 

[GameTheory]

Hi! I am new in Android development, I would like to ask how would be the code for an app "A" with a button to call an activity from another app "B" that is exported. If this activity give you access to sdcard files, how can I download those files or modify those files from the app "A". This would be for hacking demonstration purposes

You'll be using Intents. Google has guides to teach you how to do that and there are other sites on the web with tutorials.
https://developer.android.com/training/basics/intents

Read the last sentence in the first paragraph, which is what you described that you'd like to do.