At the very first run, store a variable inside a file in dirInternal for example. Every time you run your app, check for this variable (or even the existence of a file) and proceed as desired. If you are copying files from dirAssets, then just simply display your splashScreen upon copying.
Theera, your code means that splash screen is displayed every time main activity is created or recreated, not only once after installation.
But mc73 give me a good idea with a variable inside a file. Thank you.