Starting Activity from Application

Purpose: If you are logged in to your account, then we launch the main activity of the application, otherwise - login activity:

Method 1

We create additional activity, which will be the entry point of the application and we are already launching the necessary activity in it.

public class LauncherActivity extends Activity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); Class target; if (Prefs.getInstance().isLoggedIn()) { target = MainActivity.class; } else { target = LoginActivity.class; } Intent intent = new Intent(this, target); startActivity(intent); finish(); } } 

Register it in the manifest as LAUNCHER and remove it from the others.

Method 2

We leave the MainActivity as the entry point and check if the user has logged in, if not - we drop it on LoginActivity:

 public class MainActivity extends Activity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); if(!Prefs.getInstance().isLoggedIn()) { startActivity(new Intent(this, LoginActivity.class)); finish(); //обязательно } setContentView(R.layout.activity_main); // ... остальной код 

Method 3.

Actually, the opposite. We make LoginActivity an input point, if the user is logged in - we launch the main one.

 public class LoginActivity extends Activity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); if(Prefs.getInstance().isLoggedIn()) { startActivity(new Intent(this, MainActivity.class)); finish(); //обязательно } setContentView(R.layout.activity_login); // ... остальной код 

Method 4 (bad practice, unreliable)

We leave MainActivity as an entry point, but we check the Application , if it isn’t logged in, then we throw it at LoginActivity (vice versa)

 public class App extends Application { @Override public void onCreate() { super.onCreate(); if(!Prefs.getInstance().isLoggedIn()){ Intent intent = new Intent(this, LoginActivity.class); intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK); // этот флаг очистит стек активностей при переходе startActivity(intent); } } } 

I recommend using the first option, as it is more logical, activity plays the role of branching. If the logic becomes more complicated, then the second / third option will become a burden that will make your eyes callous.

Suggest your solutions))