Question

orientation change between different layouts for landscape and portrait seems to be easy, however I cannot find a solution for my current situation.

I want to use a dual-pane layout with two fragments in landscape mode

res\layout-land\dashboard_activity.xml

<?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="horizontal" >

    <fragment class="xxx.DashboardFragment"
            android:id="@+id/master_frag"
            android:layout_width="@dimen/timeline_size"
            android:layout_height="match_parent"/>

    <fragment class="xxx.TaskInstanceFragment"
            android:id="@+id/details_frag"
            android:layout_width="match_parent"
            android:layout_height="match_parent" />
</LinearLayout>

and a single-pane layout in portrait mode

res\layout\dashboard_activity.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <fragment class="xxx.DashboardFragment"
        android:id="@+id/master_frag"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        />

</FrameLayout>

I want to note that the DashboardFragment consists of a ViewPager. Do not know if it is of importance.

Now, when I change the orientation from landscape (dual) to portrait (single) the app crashes, because it wants to update the details_frag. When I start the activity in portrait, it works, only switching from landscape to portrait makes problems.

In the activity there is the following code:

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

    Fragment frag = getSupportFragmentManager().findFragmentById(R.id.details_frag);
    mDualFragments = frag != null;

    /* .. */
}

Now the FragmentManager still finds the details fragment when I switch to portrait mode and thus mDualFragments is still true but should be false, which leads to a later call to a method in the details fragment.

So, why is this? 🙂

Regards,
Konsumierer

Answer 1

Because findFragmentById not only returns the fragment in the current layout, but also previously displayed fragments. Try this instead:

mDualFragments = frag != null && frag.isInLayout();