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Put common listeners inside MainActivity class

Im interested if i can to set some common listeners inside main activity class? For my project i use FirebaseAuth, so i would like to init it in MainActivity onCreate(), setup needed listeners in onStart() and onStop(), and then inherit that class in every other activity class.
Some code to please you :]
MainActivity class [parent]:
public class MainActivity extends AppCompatActivity {
private static final String TAG = MainActivity.class.getSimpleName();
protected FirebaseAuthentication firebaseAuthentication;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
firebaseAuthentication = new FirebaseAuthentication(FirebaseAuth.getInstance(), FirebaseDatabase.getInstance());
}
#Override
protected void onStart() {
super.onStart();
firebaseAuthentication.addAuthStateListener();
}
#Override
public void onStop() {
super.onStop();
firebaseAuthentication.removeAuthStateListener();
}
}
AuthActivity class [child]:
public class AuthActivity extends MainActivity implements FirebaseAuthentication.OnUserAuthListener {
#BindView(R.id.viewPager) LockableViewPager viewPager;
private String userUID;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_market);
ButterKnife.bind(this);
firebaseAuthentication.setOnUserAuthListener(this);
firebaseAuthentication.isSingedIn(); // check if user is singed in
}
#Override
// response for firebaseAuthentication.isSingedIn() above
public void onAuthSuccess(String userUID) {
this.userUID = userUID;
}
#Override
// response for firebaseAuthentication.isSingedIn() above
public void onAuthFailure(String message) {
snackbar(message);
Intent intent = new Intent(this, AuthActivity.class);
startActivity(intent);
finish(); // TODO mb should to delete it
}
}
Can this implementations bring me errors (maybe NullPointerExeption or what unexpectedly in future)?
Would be great if you provide me some sources to read/watch.
Thank you.

Perfect example of abstraction, but not really a question.
You will not get any nullpointers or other errors by implementing it like this.

How can I call a method of an activity in another activity which not using static references?

Maybe this question is duplicate but the answers used static references to archive this. I know that static variables can cause memory leak so we should avoid using them.
How can I do that without using static method or references?

public class FirstActivity extends Activity
{
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main2);
}
// Utility.method() used somewhere in FirstActivity
}
public class Utility {
public static void method()
{
}
}
public class SecondActivity extends Activity
{
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main2);
Utility.method();
}
}

Updating dynamicaly summary preference with fragment?

I've got a problem with updating the summary value of a PreferncesFragment. I have tried to follow the advice of the post : Updating sharedPreferences Summary via listener but it doesn't work ! The summary doesn't update...
I don't understand what is wrong ? Thank's for your help !
My pref file :
<CheckBoxPreference
android:key="is_title"
android:summary="#string/conf_istitle_sum"
android:title="#string/conf_istitle_title"
android:defaultValue="true"
/>
<EditTextPreference
android:key="sms_title"
android:title="#string/conf_sms_title"
android:summary="#string/msgtitre"
android:dialogTitle="#string/conf_diagsms_title"
android:dialogMessage="#string/conf_diagsms_sum"
android:defaultValue="#string/msgtitre"
/>
My Preference class :
public class SetPreferenceActivity extends PreferenceActivity implements OnSharedPreferenceChangeListener
{
protected MyPreferenceFragment settingsFragment;
#Override
protected void onCreate(final Bundle savedInstanceState)
{ settingsFragment = new MyPreferenceFragment();
super.onCreate(savedInstanceState);
getFragmentManager().beginTransaction().replace(android.R.id.content,
settingsFragment).commit();
}
#Override
public void onSharedPreferenceChanged(SharedPreferences sharedPreferences,
String key) {
if (key.equals("sms_title")) {
String newValue = sharedPreferences.getString(key, "");
settingsFragment.findPreference(key).setSummary(newValue);
}
}
public static class MyPreferenceFragment extends PreferenceFragment
{
#Override
public void onCreate(final Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
addPreferencesFromResource(R.xml.preferences);
}
}
}
What's working is the "old" solution deprecated OldPreferences

Please check whether onSharedPreferenceChanged is being called at all. You need to register the handler with your preferences. First,
get a reference to your preferences in onCreate:
public class SettingsActivity
extends AppCompatActivity
implements SharedPreferences.OnSharedPreferenceChangeListener {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
preferences = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
// ...
}
In the lifecycle of the Activity (note that I am using a plain AppCompatActivityrather than a PreferenceActiviy) register the handeler.
#Override
protected void onPause() {
super.onPause();
preferences.unregisterOnSharedPreferenceChangeListener(this);
}
#Override
protected void onResume() {
super.onResume();
preferences.registerOnSharedPreferenceChangeListener(this);
}
Now, the handler should be called:
public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
Log.d(DEBUG_TAG, key);
// fragment.findPreference(key) //... TBD
}

Want to Run a function without click any button when application start

I have a function named 'func()'. I want to run this function when application start without clicking any button. just when application load I want to show a massage.that massage in that function. I just want to run that function when app start what will be the code.
public class TextViewActivity extends Activity {
public static EditText etxt;
public final void func(){
etxt.setText("Massage");
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
etxt= (EditText) findViewById(R.id.etxt2);
}
}

Just put a call to the function on the onCreate
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
etxt= (EditText) findViewById(R.id.etxt2);
func(); //A call to the function.
}
Hope that helps.

I don't recommend subclassing the Application in order to do this. When the application starts it will go to the main activity. So I would say just keep a SharedPreference boolean value if it has been set. If not show the message.
So keep state of the application here: http://developer.android.com/reference/android/content/SharedPreferences.html, just set a boolean. Remember when you app gets called, the activity onCreate always gets called of the main activity, so its just a matter of not calling it again.

try using below code.. you need to call ur function after you initialize edittext etxt. so it can not cause you NPE
public final void func(){
etxt.setText("Message");
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
etxt= (EditText) findViewById(R.id.etxt2);
func();// here your function call.
}

Try this:
public class TextViewActivity extends Activity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
findViewById(R.id.etxt2).setText("SMTH");
}
}
In case you really need a function to be called, you can use this:
public class TextViewActivity extends Activity {
public final void func() {
findViewById(R.id.etxt2).setText("SMTH");
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
func();
}
}

Run Method when Preference is Updated

How would I add a listener so that when a preference is changed (i.e. CheckBoxPreference) some
method is executed (i.e. Toast)
Preferences.java
public class Preferences extends PreferenceActivity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
addPreferencesFromResource(R.xml.preferences);
}
}
Main.java
[...]
SharedPreferences preferences;
preferences = PreferenceManager.getDefaultSharedPreferences(this);
[...]

http://developer.android.com/resources/samples/ApiDemos/src/com/example/android/apis/app/AdvancedPreferences.html