Question

I tried to find out how to safely assert that preferences aren’t stored anywhere. It seems that haven’t understood the caching mechanism yet and the docs don’t clarify it. This is what I did:

File prefsFile = new File("/data/data/"+context.getPackageName() + "/shared_prefs/"
    + context.getPackageName() + "_preferences.xml");
prefsFile.delete();
assertFalse(prefsFile.exists()); // success

// This assertion could fail - why?
assertEquals(0, context.getSharedPreferences(context.getPackageName()+"_preferences",
    MODE_PRIVATE).getAll().size());

Although I deleted the prefs file, it is still possible that getAll().size() returns a non-zero value.

Could someone explain why?

Answer 1

I tried to find out how to safely assert that preferences aren’t stored anywhere.

Why?

Could someone explain why?

Off the top of my head:

• You are not actually testing to see if the file exists before deleting it, or if the directory exists
• You are hard-coding a path that may not be correct on all devices
• You are assuming that deleting a file deletes the in-process copy of the SharedPreferences
• You are not bothering to look at the HashMap returned by getAll() to see if your data is there, or if it is some system-supplied initial values

If you want to clear out SharedPreferences, do not try deleting the file. Either call edit().clear().commit() or edit().clear().apply() on your SharedPreferences object.