Question

I am learning how to set up preferences in an android application. I have a file res/xml/prefs.xml with a few different component(?) things in it. This is referenced by Prefs.java, which uses addPreferencesFromResource(R.xml.prefs); in its onCreate() method. As I understand, the prefs.xml file sets up the preferences, and the Prefs.java file accesses the prefs.xml to give it logic (that I would then program).
Then in my Manifest, I have one of the activities as

<activity
    android:name=".Prefs"
    android:label="Preferences" >
    <intent-filter>
        <action android:name="com.example.lesson1.PREFS" />
        <category android:name="android.intent.category.DEFAULT" />
    </intent-filter>
</activity>

Not really sure if Manifest references Prefs.java or if it’s the other way around or what.

In addition (the most confusing right now), I have another file called Splash.java, which displays a splash screen. On the splash screen’s onCreate(), it does this:

    MediaPlayer ourSong = MediaPlayer.create(Splash.this, R.raw.splash);
    SharedPreferences getPrefs = PreferenceManager
            .getDefaultSharedPreferences(getBaseContext()); 
    boolean music = getPrefs.getBoolean("checkbox", true);
    if (music) {
        ourSong.start();
    }

I’m not really sure how this knows where the preferences (any one of them, or whichever one it references to) are. I never told it that prefs.xml is the preferences file, or where it is. So is this a default that the preferences are in res/xml/prefs.xml and it knows that automatically?
I’m just really confused aboout the whole order of things. Which file references which? How does the manifest come into play here (it seems like it just points to the .java file to tell the android app that it’s there, but i don’t really know). And finally, is it possible to state that the preferences are in a different .java and .xml file, or do they have to be called prefs.java/.xml?

Thanks, sorry if this is confusing. I’m pretty confused myself and can’t really tell if I’m making sense completely here.

Answer 1

When your app is compiled, various things in the res folder are compiled in. In this case the xml folder is recognized as a raw folder and R.xml.prefs is added to the autogenerated code.

At runtime, this is treated as a raw resource and the data is read in (it’s actually built using an inflater, similar to how the layout inflater works). You can actually see the data yourself, using…

InputStream is = context.getResources().openRawResource(R.xml.prefs);

So at runtime, addPreferencesFromResource(R.xml.prefs) is enough for the preferences to be loaded.

As for accessing the preferences, the preferences are stored in SharedPreferences. I assume you have a preference called “checkbox”, so when you call getPrefs.getBoolean("checkbox", true) it looks for that SharedPreference value, if not found (because preferences haven’t been set yet), then it returns true (the second argument).

This is why it’s super important for you to be consistent in your defaults. It’s actually probably worth having a class dedicated to interfacing with the preferences so that you don’t accidentally default to different values in different places.

There is a lot of auto-generation magic in the res folder. For example, everyone uses res/values/strings.xml to store their strings, but it doesn’t actually matter what the filename is. Anything in res/values/ is read and merged, and each file can be a mixture of all sorts of data types (strings, integers, colors, etc.)