Androidx ViewPager2 不兼容类型：ViewPagerAdapter 无法转换为 Adapter

Question

I am using ViewPager2, and I get the following error on viewPager2.setAdapter :

incompatible types: ViewPagerAdapter cannot be converted to Adapter

MainActivty

viewPagerAdapter = new ViewPagerAdapter(getSupportFragmentManager(),fragmentList);
viewPager2.setAdapter(viewPagerAdapter);

ViewPagerAdapter

public class ViewPagerAdapter extends FragmentStatePagerAdapter {

    private List<PagerFragment> fragments;


    public ViewPagerAdapter(FragmentManager fm, List<PagerFragment> fragments) {
        super(fm);
        this.fragments = fragments;
    }

    /* (non-Javadoc)
     * @see android.support.v4.app.FragmentPagerAdapter#getItem(int)
     */
    @Override
    public Fragment getItem(int position) {
        return this.fragments.get(position);
    }

    /* (non-Javadoc)
     * @see android.support.v4.view.PagerAdapter#getCount()
     */
    @Override
    public int getCount() {
        return this.fragments.size();
    }
}

Answer 1

You're trying to use a ViewPager v1 adapter with ViewPager2 . You should convert your adapter to implement FragmentStateAdapter instead.

See this section of the migration documentation for more information. In particular, you'll want to rename your getCount method to getItemCount , as well as renaming getItem to createFragment and making it return a new Fragment each time rather than re-using instances.

Answer 2

public class ViewPagerAdapter extends FragmentPagerAdapter {

private ArrayList<Fragment> fragments;
private ArrayList<String> titles;

public ViewPagerAdapter(FragmentManager fm){
    super(fm);
    this.fragments=new ArrayList<>();
    this.titles=new ArrayList<>();

}


@NonNull
@Override
public Fragment getItem(int position) {
    return fragments.get(position);
}

@Override
public int getCount() {
    return fragments.size();
}


public void addFragment(Fragment fragment, String title){

    fragments.add(fragment);
    titles.add(title);

}

@Nullable
@Override
public CharSequence getPageTitle(int position) {
    return titles.get(position);
}

}