Swipeable ViewPager with ActionBar Tabs (Null Object Reference)

Question

I tried to follow a tutorial how to create a swipeable ViewPager with ActionBar Tabs. Everything is compiling fine, but when I try to start the activity, it crashes with this error:

Attempt to invoke virtual method 'void android.support.v4.view.ViewPager.setAdapter(android.support.v4.view.PagerAdapter)' on a null object reference

This is my adapter:

public class TabsPagerAdapter extends FragmentPagerAdapter {

public TabsPagerAdapter(FragmentManager fm) {
    super(fm);
}

@Override
public Fragment getItem(int index) {

    switch (index) {
    case 0:
        return new WeekFragment();
    case 1:
        return new MonthFragment();
    case 2:
        return new YearFragment();
    }

    return null;
}

@Override
public int getCount() {
    // get item count - equal to number of tabs
    return 3;
}}

Part of my MainActivity:

viewPager = (ViewPager) findViewById(R.id.pager);
mAdapter = new TabsPagerAdapter(getSupportFragmentManager());
viewPager.setAdapter(mAdapter);

I know this question has been asked many times ago, but nothing works. I don't know, why this is not working! Please help me. I'm now sitting here for more than 2 hours and still haven't found a solution ...

Answer 1

Okay, now I found out why this error happened. I set the wrong contentView. Therefore viewPager was indeed null. Smallest things make biggest problems.

Anyway, thank you for your help, guys!

Perhaps someone has the same problem I had.