First fragment to be added to the main activity when application starts up

Question

Suppose I am creating an Android application which has a Navigation drawer and set of fragments. When user clicks on an option in the

Answer 1

You just perform the same FragmentTransaction you use to replace the fragment on user interaction and in the onCreate() method of your Activity. But you have to check if savedInstanceState is null like this:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    if(savedInstanceState == null) {
        FragmentManager manager = getFragmentManager();
        FragmentTransaction transaction = manager.beginTransaction();
        transaction.replace(R.id.flFragmentContainer, MainFragment.newInstance());
        transaction.commit();
    }
}