CODEWITHSUNDEEP
androidandroid-viewpager
Maarten
Maarten

Reputation: 7338

Must ViewPagers have a unique id within their Activity? (If they're backed by a FragmentStatePagerAdapter)

I have an activity with two ViewPagers both working with a FragmentStatePagerAdapter. But when the ViewPagers have no id, or both have the same id, they will not work correctly.

Activity layout (activity.xml):

<LinearLayout 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"
    android:orientation="vertical"
    tools:context="com.example.app.MainActivity">

    <FrameLayout
            android:id="@+id/frame1"
            android:layout_width="match_parent"
            android:layout_weight="1"
            android:layout_height="0dp">

       <include layout="@layout/merge_pager" />

     </FrameLayout>

     <FrameLayout
        android:id="@+id/frame2"
        android:layout_width="match_parent"
        android:layout_weight="1"
        android:layout_height="0dp">

        <include layout="@layout/merge_pager" />

    </FrameLayout>

</LinearLayout>

Merge layout (merge_pager.xml):

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

    <android.support.v4.view.ViewPager
        android:id="@+id/view_pager"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</merge>

Activity:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity);
    FrameLayout frame1 = (FrameLayout) findViewById(R.id.frame1);
    FrameLayout frame2 = (FrameLayout) findViewById(R.id.frame2);

    ViewPager vp1 = (ViewPager) frame1.getChildAt(0);
    ViewPager vp2 = (ViewPager) frame2.getChildAt(0);

    if (vp1 == null | vp2 == null) {
        throw new NullPointerException();
    }
    vp1.setAdapter(new ColorAdapter(getSupportFragmentManager()));
    vp2.setAdapter(new ColorAdapter(getSupportFragmentManager()));
}

private class ColorAdapter extends FragmentStatePagerAdapter {
    public ColorAdapter(FragmentManager fragmentManager) {
        super(fragmentManager);
    }

    @Override
    public Fragment getItem(int i) {
        return new ColorFragment();
    }

    @Override
    public int getCount() {
        return Integer.MAX_VALUE;
    }
}

public static class ColorFragment extends Fragment {
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        TextView tv = new TextView(container.getContext());
        Drawable d = new ColorDrawable(randomColor());
        tv.setBackgroundDrawable(d);
        return tv;
    }

public static int randomColor() {
    return Color.rgb(random255(), random255(), random255());
}

public static int random255() {
    return
            (int) (Math.random() * (double) 255);
}

Using this code, the second ViewPager won't work. I suspected it might be due to clashing ids (R.id.view_pager), so I removed the id from the merge file. However, this results in a fatal exception:

 FATAL EXCEPTION: main
    android.content.res.Resources$NotFoundException: Unable to find resource ID #0xffffffff

What is up with this?

Upvotes: 1

Views: 246

Answers (1)

Maarten
Maarten

Reputation: 7338

It says in the docs:

When using FragmentPagerAdapter the host ViewPager must have a valid ID set.

So at least it's documented that the adapter won't work without an id for its pager. I suppose you can then take 'valid' to mean 'unique in the activity view hierarchy'.

Upvotes: 1

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