BooleanSharedPreferenceLiveData.java

abstract class SharedPreferenceLiveData<T> extends LiveData<T> {

    SharedPreferences sharedPrefs;
    String key;
    T defValue;

    public SharedPreferenceLiveData(SharedPreferences prefs, String key, T defValue) {
        this.sharedPrefs = prefs;
        this.key = key;
        this.defValue = defValue;
    }

    private SharedPreferences.OnSharedPreferenceChangeListener preferenceChangeListener = new SharedPreferences.OnSharedPreferenceChangeListener() {
        @Override
        public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
            if (SharedPreferenceLiveData.this.key.equals(key)) {
                setValue(getValueFromPreferences(key, defValue));
            }
        }
    };
    abstract T getValueFromPreferences(String key, T defValue);

    @Override
    protected void onActive() {
        super.onActive();
        setValue(getValueFromPreferences(key, defValue));
        sharedPrefs.registerOnSharedPreferenceChangeListener(preferenceChangeListener);
    }

    @Override
    protected void onInactive() {
        sharedPrefs.unregisterOnSharedPreferenceChangeListener(preferenceChangeListener);
        super.onInactive();
    }

}

public class SharedPreferenceBooleanLiveData extends SharedPreferenceLiveData<Boolean>{

    public SharedPreferenceBooleanLiveData(SharedPreferences prefs, String key, Boolean defValue) {
        super(prefs, key, defValue);
    }

    @Override
    Boolean getValueFromPreferences(String key, Boolean defValue) {
        return sharedPrefs.getBoolean(key, defValue);
    }
}

Hello, I would like to implement your example above. How do you observe for the updates. Do you have an example of code I could use to put in my activity / fragment ?
I do not see any function returning a livedata I could observe. (Ok I must admit I'm not an expert :-)
Thx for your help.

I answer to myself with what I did:

 SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(this);
 SharedPreferenceStringLiveData sharedPreferenceStringLiveData = new SharedPreferenceStringLiveData(preferences, "cid", "");
 sharedPreferenceStringLiveData.getStringLiveData("cid", "").observe(this, cid -> {
            Toast.makeText(this, "Change in CID "+cid, Toast.LENGTH_SHORT).show();
 });

In SharedPreferenceLiveData, I included a new function :

public SharedPreferenceLiveData<String> getStringLiveData(String key, String defaultValue) {
    return new SharedPreferenceStringLiveData(sharedPreferences, key, defaultValue);
 }

Not sure this is the right way to do. In addition, I do not see why we need to pass key and defaultvalue in the constructor.

SharedPreferenceLiveData should extends MutableLiveData?, or am i wrong?

SharedPreferenceLiveData should extends MutableLiveData?, or am i wrong?
You don not need extend MutableLiveData. setValue and postValue are protected, so you can use them as long as you extend LiveData.

How do you use this with Transformation switchmap? I would like to use it with my ViewModel and the ViewModel needs to be aware of changes.