S.D. S.D. - 2 months ago 21
Android Question

Empty ViewPager crashes with PagerTabStrip

When using a

ViewPager
with
PagerTabStrip
:

<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.view.ViewPager
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/pager"
android:layout_width="fill_parent"
android:layout_height="fill_parent">

<android.support.v4.view.PagerTabStrip
android:id="@+id/pager_tab_strip"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_gravity="top"
android:paddingTop="4dp"
android:paddingBottom="4dp"
/>

</android.support.v4.view.ViewPager>


with pager having an empty adapter:

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

ViewPager pager = (ViewPager) findViewById(R.id.pager);

FragmentPagerAdapter adapter = new FragmentPagerAdapter(getFragmentManager()) {

@Override
public CharSequence getPageTitle(int position) {
return "test";
}

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

@Override
public int getCount() {
return 0;
}
};
pager.setAdapter(adapter);

}


App crashes on touching/scrolling the Tab Strip:

java.lang.IndexOutOfBoundsException: Invalid index 0, size is 0
at java.util.ArrayList.throwIndexOutOfBoundsException(ArrayList.java:251)
at java.util.ArrayList.get(ArrayList.java:304)
at android.support.v4.view.ViewPager.performDrag(ViewPager.java:1990)


I think this line in
ViewPager.performDrag()
might be the cause.

Is it a bug or something wrong with my view setup ?

Answer

In ViewPager code array items are accessed without any checks (when there is no page ):

final ItemInfo firstItem = mItems.get(0);
final ItemInfo lastItem = mItems.get(mItems.size() - 1);

This causes it to crash.