Assuming your file doesn't (always) exist you should probably put your observer on the files folder, obtained like so:
Context ctx = ...;
File filesFolder = ctx.getFilesDir();
Note that this will also ensure that the filesFolder
directory will be created.
Your observer will now be notified whenever a file is written, deleted or updated using for instance Context#.openFileOutput(..)
- and you can filter in your FileObserver
for the file name, in your example "quest".