iOS AppDelegate equivalent in Android

You have to create your own subclass of Application and specify it in the AndroidManifest.xml. After that the new instance of this class will be created and can be accessed throughout your application.

Example:

Manifest.xml

<application name="YourApp"> 

YourApp.java

public class YourApp extends Application {
    private String yourState;
 
    public void setState(String state){
        yourState = state;
    }
    public String getState(){
        return yourState;
    }
 }
 

YourActivity.java

 public class YourActivity extends Activity {
    @Override
    public void onCreate(Bundle bundle){
        YourApp appState = ((YourApp)getApplicationContext());// you can use getApplication() as well in the activity
        String state = appState.getState();
    }
 }

More info about Application

Make your main class implement ProcessLifecycleObserver.

It is the equivalent of the AppDelegate in iOS as it "summarizes" activity handlers like onCreate, onResume on an app-process basis.

https://developer.android.com/reference/android/arch/lifecycle/ProcessLifecycleOwner

You should be creating a model object (your own class) to retain the data on both iOS and android. imho.