How to detect if changes were made in the preferences?

Question

I have a class that extends PreferenceActivity and shows the preference screen of my app. Is it possible to check if any changes were made to the preferences?

This helps...

http://developer.android.com/reference/android/content/SharedPreferences.OnSharedPreferenceChangeListener.html

Other related post: SharedPreferences.onSharedPreferenceChangeListener not being called consistently

---

public class PreferenceClass extends PreferenceActivity {

    OnSharedPreferenceChangeListener listener;

    public void onCreate(Bundle savedInstanceState) {
        SharedPreferences prefs = this.getSharedPreferences("settings", 0);
        listener = new SharedPreferences.OnSharedPreferenceChangeListener() {

            public void onSharedPreferenceChanged(SharedPreferences prefs, String key) {
                int flag = 1;
            }
        };
        prefs.registerOnSharedPreferenceChangeListener(listener);
        super.onCreate(null);
        addPreferencesFromResource(R.xml.settings);
    }
}

Solution 1

Do

SharedPreferences.OnSharedPreferenceChangeListener spChanged = new
                           SharedPreferences.OnSharedPreferenceChangeListener() {
            @Override
    public void onSharedPreferenceChanged(SharedPreferences sharedPreferences,
            String key) {
        // your stuff here
    }
};

In your PreferenceActivity, ie make it a member of your PreferenceActivity class and then do registerOnSharedPreferenceChangeListener(spChanged) in the PreferenceActivity.onCreate() method.

That's what I do and I never have a problem.

Else it's your conditional checking in the listener that is at fault. Post the code.

EDIT:

From the code you posted, you should make prefs a class member variable so it has a global scope.

And do prefs = PreferenceManager.getDefaultSharedPreferences(getApplicationContext()); instead of getSharedPreferences because you haven't created that file.

To create a file you need to use PreferenceManager. To get a PreferenceManager, use Activity.getPreferenceManager().

Solution 2

In your PreferenceActivity class, implement the SharedPreferences.OnSharedPreferenceChangeListener interface. Add the required onSharedPreferenceChanged method to your class and register it in the onCreate.

See sample code here:

public class MyPreferences extends PreferenceActivity implements SharedPreferences.OnSharedPreferenceChangeListener {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        addPreferencesFromResource(R.xml.fw_preferences); //deprecated
        PreferenceManager.getDefaultSharedPreferences(this).registerOnSharedPreferenceChangeListener(this);
    }

    @Override
    public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
        // handle the preference change here
    }

}

Comments

[R Hughes]

I see too many directions this could possibly go depending on your overall goal. Could you toss out some specifics about when you are checking and to what end?

[mixkat]

@RHughes I just want everytime a change is made to do something...Just found this link stackoverflow.com/questions/2542938/…... Still cant get it to work though...the method in the listener never gets called...Any ideas???

[R Hughes]

Without looking at the code, I can only guess that you are making the same mistake I always seem to make. I build a great listener then forget to attach it to the right object. Also, make sure you are attaching the listener to the object in the onCreate() method or at least in code that you run BEFORE you actually need the listener to be listening.

[mixkat]

@RHughes No Im attaching the listener to the object...donno whats wrong with it...its definitely on create...anyways thanks for the reply...

[mixkat]

@sugarynugs Thats exactly what I am doing...in fact i copied the code from this other post...

[mixkat]

@sugarynugs listener = new SharedPreferences.OnSharedPreferenceChangeListener() { public void onSharedPreferenceChanged(SharedPreferences prefs, String key) { // Implementation } }); prefs.registerOnSharedPreferenceChangeListener(listener)

[mixkat]

@sugarynugs listener is an instance variable of this class..just to avoid it being gc..

[techi.services]

where is the variable declaration? Is it a Global? Plus wrong code posted... the bit inside the listener.

[mixkat]

That was it...getDefaultSharedPreferences fixed it....thanks a lot mate... @sugarynugs

[babay]

don't forget to UNREGISTER listener with .unregisterOnSharedPreferenceChangeListener !!!

[mattecalcio]

How would you refactor the deprecated line you have in your code? addPreferencesFromResource(R.xml.fw_preferences); //deprecated

[Admin]

@mattecalcio I know I'm late but here is the new way to load in a settings xml: stackoverflow.com/a/13441715/1318194

[RenniePet]

@babay: Just wondering if you know if there is any need to try to unregister the listener if it is implemented in the Application class? (Doing that would be very difficult - the Application class has no onStop() or onDestroy() methods.)

[babay]

@RenniePet, No, you don't have to unregister preferences listener that is registered in Application class. For example, It you don't unregister a listener in Activity class, then garbage collector will not release memory allocated by Activity object after activity closed (preference manager has a reference to listener, listener has a reference to activity). But your don't have that case with Application class.

[Andrii Kovalchuk]

Is it a good practice to do unregisterOnSharedPreferenceChangeListener(this) in onDestroy() of MainActivity?

[mehmet]

your answer awesome but also docs says: add register part in resume and add unregister part in pause for garbage colecter. thanks again developer.android.com/guide/topics/ui/…

[MRodrigues]

Together with implementing the interface OnSharedPreferenceChangeListener and register listener on onResume and unregister on onPause

[Cícero Moura]

Don't forget to call PreferenceManager.getDefaultSharedPreferences(this).unregist‌​erOnSharedPreference‌​ChangeListener(this)‌​; on onDestroy or implement like @MRodrigues put above