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android – Fragments restore state on orientation changed

Posted by: admin May 14, 2020 Leave a comment

Questions:

I have to implement “standart” fragments navigation in my app (please see link).

The issue is when device is in portrait mode, there should be shown only 1 fragment, and when it is rotated to landscape mode, 2 fragments should be shown.

I tried to do this 2 different ways:

1) I use only 1 activity with different portrait and landscape layouts.

Portrait layout xml:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

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

</RelativeLayout>

And here`s landscape layout:

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

    <FrameLayout
        android:id="@+id/main_frame_fragment_container_left"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="1" />

    <FrameLayout
        android:id="@+id/main_frame_fragment_container_right"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="1" />

</LinearLayout>

Activity`s onCreate method:

    private static ItemsFragment mItemsFragment;
    private static ItemDetailsFragment mItemDetailsFragment;

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

        if (mItemsFragment == null) {
            mItemsFragment = ItemsFragment.newInstance();
        }
        if (mItemDetailsFragment == null) {
            mItemDetailsFragment = ItemDetailsFragment.newInstance();
        }

        if (isLandscape()) {
            getSupportFragmentManager().beginTransaction().replace(R.id.main_frame_fragment_container_left, mItemsFragment)
                    .commit();
            getSupportFragmentManager().beginTransaction()
                    .replace(R.id.main_frame_fragment_container_right, mItemDetailsFragment).commit();
        } else {
            getSupportFragmentManager().beginTransaction().replace(R.id.main_frame_fragment_container, mItemsFragment)
                    .commit();
        }
    }

And that`s the way I refresh 2nd fragment:

Bundle bundle = new Bundle();
bundle.putSerializable(BaseFragment.KEY_BUNDLE_ITEM, response.getItem());
mItemDetailsFragment = ItemDetailsFragment.newInstance(bundle);
if (isLandscape()) {
    getSupportFragmentManager().beginTransaction()
                            .replace(R.id.main_frame_fragment_container_right, mItemDetailsFragment).commit();
} else {
    getSupportFragmentManager().beginTransaction()
                            .replace(R.id.main_frame_fragment_container, mItemDetailsFragment).addToBackStack(null).commit();
}

Also I save and restore fragments` states, so my data does not disappear after rotations. Generally, this code works properly in my case.

2) I use 2 activities and the same layout for 1st Activity portrait and landscape modes.

xml layout is the same as in previous one for landscape:

    <FrameLayout
        android:id="@+id/main_frame_fragment_container_left"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="1" />

    <FrameLayout
        android:id="@+id/main_frame_fragment_container_right"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="1" />

</LinearLayout>

onCreate method (note, that fragments entities are not static, as it was in 1st case):
private ItemsFragment mItemsFragment;
private ItemDetailsFragment mItemDetailsFragment;

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

    if (savedInstanceState == null) {
        mItemsFragment = ItemsFragment.newInstance();
        mItemDetailsFragment = ItemDetailsFragment.newInstance();

        getSupportFragmentManager().beginTransaction().replace(R.id.main_frame_fragment_container_left, mItemsFragment)
        .commit();
        getSupportFragmentManager().beginTransaction()
        .replace(R.id.main_frame_fragment_container_right, mItemDetailsFragment).commit();
    }
}

And now if the device is in portrait mode, I start new Activity:

if (isLandscape()) {
    Bundle bundle = new Bundle();
    bundle.putSerializable(BaseFragment.KEY_BUNDLE_ITEM, response.getItem());
    mItemDetailsFragment = ItemDetailsFragment.newInstance(bundle);
    getSupportFragmentManager().beginTransaction()
        .replace(R.id.main_frame_fragment_container_right, mItemDetailsFragment).commit();
} else {
    Intent intent = new Intent(getApplicationContext(), DetailsActivity.class);
    intent.putExtra(KEY_ITEM, response.getItem());
    startActivity(intent);
}

And, at last, 2nd Activity`s onCreate method:

protected void onCreate(Bundle arg0) {
    super.onCreate(arg0);
    setContentView(R.layout.activity_details);

    if (isLandscape()) {
        finish();
    }

    Item item = (Item) getIntent().getExtras().getSerializable(KEY_ITEM);

    Bundle bundle = new Bundle();
    bundle.putSerializable(BaseFragment.KEY_BUNDLE_ITEM, item);

    ItemDetailsFragment mItemDetailsFragment = ItemDetailsFragment.newInstance(bundle);

    getSupportFragmentManager().beginTransaction()
        .replace(R.id.main_frame_fragment_container, mItemDetailsFragment).commit();
}

When device is rotated to landscape mode, 2nd activity finishes, and I see my 1st activity with 2 fragments (as expected).

Question:

In 1st case I save fragments as static variables, and because of this I don’t care if I change 2nd fragment state in portrait or landscape modes (the same fragment is used). But I don’t think it’s a good idea to save it as static fields.

In 2nd case I don’t know how to sync Activity A Fragment B (landscape) and Activity B Fragment B (portrait). If I change something in fragment (I mean, toggle button etc) and rotate device, changes should be applied in another fragment.

Generally, what case is better, and if 2nd, how can I resolve synchronization issue? Or maybe there is another easier way. Thanks for reading, I hope you can help me 🙂

How to&Answers:

Just follow this mate http://developer.android.com/guide/components/fragments.html. Dont make fragments static (thats just wierd)