Hide / Show fragment with fragmentTransaction not working

Question

I want my activity to contain 2 fragments, and to switch between them with a button at the action bar. So here is my activity's layout:

<?xml version="1.0" encoding="utf-8"?>

    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
                  android:layout_width="match_parent"
                  android:layout_height="match_parent"
                  android:orientation="vertical">

        <FrameLayout
            android:id="@+id/fragment_container"
            android:layout_width="match_parent"
            android:layout_height="match_parent" />

</LinearLayout>

At the activity's onCreate() I add both fragments to the container... As I need the firstFragment to execute before secondFragment, I'm adding it first, and than hiding secondFragment so user will see fragments in the proper order:

if (findViewById(R.id.fragment_container) != null) {
        if (savedInstanceState != null) {
            return;
        }
        FirstFragment firstFragment = new FirstFragment();
        SecondFragment secondFragment = new SecondFragment();
        firstFragment.setArguments(getIntent().getExtras());
        getSupportFragmentManager().beginTransaction()
                .add(R.id.fragment_container, firstFragment, "FirstFragment")
                .add(R.id.fragment_container, secondFragment, "SecondFragment")
                .hide(secondFragment)
                .commit();
    }

When user touches a button at the action bar, the following method gets executed and was supposed to hide one fragment and show the other one, but nothing happens...

public void changeFragment(int id){
    Fragment secondFragment = new SecondFragment();
    Fragment firstFragment = new FirstFragment();
    FragmentTransaction transaction = getSupportFragmentManager().beginTransaction()
            .setCustomAnimations(android.R.anim.fade_in, android.R.anim.fade_out);
    switch (id){
        case 1:
            //show 2nd
            transaction.hide(firstFragment)
                    .show(secondFragment)
                    .commit();
            break;
        case 2:
            //show 1st
            transaction.hide(secondFragment)
                    .show(firstFragment)
                    .commit();
            break;
        default:
            //do nothing
    }
}

Any hint on what I'm missing here? Thanks in advance

Answer 1

Actually, your problem looks trivial. Every time you're creating new fragments by:

public void changeFragment(int id){
    Fragment secondFragment = new SecondFragment();
    Fragment firstFragment = new FirstFragment();

I think the code should be like that, because You just want to hide one and show another, but not add two absolutely new fragments:

public void changeFragment(boolean id){
    final Fragment secondFragment = getFragmentManager().findFragmentByTag(FIRST_FRAGMENT_TAG);
    final Fragment firstFragment = getFragmentManager().findFragmentByTag(SECOND_FRAGMENT_TAG);