How to listen for preference changes within a PreferenceFragment?

Question

As described here, I am subclassing PreferenceFragment and displaying it inside an Activity. That document explains how to listen for preference changes here, but only if you subclass PreferenceActivity. Since I'm not doing that, how do I listen for preference changes?

I've tried implementing OnSharedPreferenceChangeListener in my PreferenceFragment but it does not seem to work (onSharedPreferenceChanged never seems to get called).

This is my code so far:

SettingsActivity.java

public class SettingsActivity extends Activity
{
    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);

        // Display the fragment as the main content.
        getFragmentManager().beginTransaction().replace(android.R.id.content, new SettingsFragment()).commit();
    }
}

SettingsFragment.java

public class SettingsFragment extends PreferenceFragment implements OnSharedPreferenceChangeListener
{
    public static final String KEY_PREF_EXERCISES = "pref_number_of_exercises";

    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);

        // Load the preferences from an XML resource
        addPreferencesFromResource(R.xml.preferences);
    }

    @Override
    public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key)
    {
        //IT NEVER GETS IN HERE!
        if (key.equals(KEY_PREF_EXERCISES))
        {
            // Set summary to be the user-description for the selected value
            Preference exercisesPref = findPreference(key);
            exercisesPref.setSummary(sharedPreferences.getString(key, ""));
        }
    }
}

preferences.xml

<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android" >

    <EditTextPreference
        android:defaultValue="15"
        android:enabled="true"
        android:key="pref_number_of_exercises"
        android:numeric="integer"
        android:title="Number of exercises" />

</PreferenceScreen>

Also, is the PreferenceFragment even the right place to listen for preference changes or should I do it within the Activity?

Solution 1

I believe you just need to register/unregister the Listener in your PreferenceFragment and it will work.

@Override
public void onResume() {
    super.onResume();
    getPreferenceManager().getSharedPreferences().registerOnSharedPreferenceChangeListener(this);

}

@Override
public void onPause() {
    getPreferenceManager().getSharedPreferences().unregisterOnSharedPreferenceChangeListener(this);
    super.onPause();
}

Depending on what you want to do you may not need to use a listener. Changes to the preferences are committed to SharedPreferences automatically.

Solution 2

The solution of antew works well, here you can see a full preference activity for Android v11 onwards:

import android.app.Activity;
import android.content.SharedPreferences;
import android.content.SharedPreferences.OnSharedPreferenceChangeListener;
import android.os.Bundle;
import android.preference.ListPreference;
import android.preference.PreferenceFragment;

public class UserPreferencesV11 extends Activity  {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    // Display the fragment as the main content.
    getFragmentManager().beginTransaction().replace(android.R.id.content,
            new PrefsFragment()).commit();
}

public static class PrefsFragment extends PreferenceFragment implements OnSharedPreferenceChangeListener {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // Load the preferences from an XML resource
        addPreferencesFromResource(R.xml.preferences);

        // set texts correctly
        onSharedPreferenceChanged(null, "");

    }

    @Override
    public void onResume() {
        super.onResume();
        // Set up a listener whenever a key changes
        getPreferenceScreen().getSharedPreferences().registerOnSharedPreferenceChangeListener(this);
    }

    @Override
    public void onPause() {
        super.onPause();
        // Set up a listener whenever a key changes
        getPreferenceScreen().getSharedPreferences().unregisterOnSharedPreferenceChangeListener(this);
    }

    @Override
    public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
        // just update all
        ListPreference lp = (ListPreference) findPreference(PREF_YOUR_KEY);
        lp.setSummary("dummy"); // required or will not update
        lp.setSummary(getString(R.string.pref_yourKey) + ": %s");

    }
}
}

Solution 3

All the other answers are correct. But I like this alternative better because you immediately have the Preference instance that caused the change.

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    Preference pref = findPreference(getString(R.string.key_of_pref));        
    pref.setOnPreferenceChangeListener(new Preference.OnPreferenceChangeListener() {
        @Override
        public boolean onPreferenceChange(Preference preference, Object newValue) {
            // do whatever you want with new value

            // true to update the state of the Preference with the new value
            // in case you want to disallow the change return false
            return true;
        }
    });
}

Solution 4

This worked for me from PreferenceFragment.onCreate()

OnSharedPreferenceChangeListener listener = 
    new SharedPreferences.OnSharedPreferenceChangeListener()
    {
        public void onSharedPreferenceChanged(SharedPreferences prefs, String key)
        {
         showDialog();
        }
    };

Solution 5

Here is one way to do it and avoid any potential memory leaks:

@Override
public void onCreatePreferences(Bundle savedInstanceState, String rootKey) {
    addPreferencesFromResource(R.xml.pref_movies);

    SharedPreferences sharedPreferences = getPreferenceScreen().getSharedPreferences(); 

    //starts live change listener
    sharedPreferences.registerOnSharedPreferenceChangeListener(this);
}

@Override
public void onDestroyView () {
    super.onDestroyView(); 
//Unregisters listener here
    PreferenceManager.getDefaultSharedPreferences(getContext())
            .unregisterOnSharedPreferenceChangeListener(this);
}

View more solutions

Comments

[XåpplI'-I0llwlg'I -]

Ah, I see. That works. But should I be getting the SharedPreferences via getPreferenceManager (like you've done) or getPreferenceScreen? What's the difference?

[antew]

To be honest I'm not sure what the real difference is, perhaps someone else can weigh in on it, it could be a good topic for another question as well.

[XåpplI'-I0llwlg'I -]

Okay, here is an answer to that question. It looks like there is absolutely no functional difference, but getPreferenceManager is generally the preferred option.

[srv_sud]

when the settings-preference is created for the first time, the summary is not set as per the stored preference value. How to resolve this??

[Jose_GD]

@srv_sud inside your onCreate() call onSharedPreferenceChanged() directly

[srv_sud]

@Jose_GD : what instance of pref and let to pass in that method. Because in my onShardPrefChanged() I'll process the data before updation differently for different keys.

[Jose_GD]

Correct, although in onSharedPreferenceChanged () you can access the Preference instance easily with findPreference(key). Maybe the SharedPreferences way is preferred because of the registering/unregistering thing?

[Jose_GD]

@srv_sud you mean what the key parameter should be? Haven't tried this, you have an example in Gunnar's answer below: onSharedPreferenceChanged(null, ""). It may not be suitable to your needs. Perhaps you should iterate on your keys of preferences that need an update

[srv_sud]

@Jose_GD: ya.. i think i need to iterate .. thanks for the answer.

[Bryan W]

In onPause, should the super.onPause() be called before or after the listener is unregistered? Is there even a difference? I've seen both in numerous examples

[Studio2bDesigns]

@BryanWalsh I've also seen examples of both ways.. I would think unregistering the listerner before calling super.onPause(); is probably the best way to go about it.

[pete]

why is unregistering necessary?

[josef]

There is no this in a static class!

[Gunnar Bernstein]

Can you elaborate on that? I absolutely have no clue which "this" you are referring to. The answer is 7 years old. Android has changed a lot.

[josef]

public static class PrefsFragment declares a static class and then uses this inside to reference itself. But that is not possible, you can not use this within a static class.

[Gunnar Bernstein]

Are you sure you understood the concept of static inner classes in Java? A static nested class may be instantiated without instantiating its outer class. Using 'this' is perfectly fine. This is not C#!

[josef]

I am not sure, but I tried the code in Android Studio and it complains on the this: " getPreferenceScreen().getSharedPreferences().registerOnShare‌​dPreferenceChangeLis‌​tener(this);". I had to rewrite the code to get it to compile.