Why can a class member lost its value in Android?

Question

Can someone explain me why can sometimes this exception happen?

Exception java.lang.NullPointerException: Attempt to invoke virtual method 'long java.util.Date.getTime()' on a null object reference

ChannelEPGF$myPagerAdapter.getItem (ChannelEPGF.java:82) (find the "//THIS IS THE 82. rows" text in my code)

here is my code:

    import android.os.Bundle;
    import android.support.v4.app.Fragment;
    import android.support.v4.app.FragmentManager;
    import android.support.v4.app.FragmentPagerAdapter;
    import android.support.v4.view.ViewPager;
    import android.view.LayoutInflater;
    import android.view.View;
    import android.view.ViewGroup;
    import com.mp.myapp.DataTypes.ChannelEPG;
    import java.util.Date;

    public class ChannelEPGF extends Fragment implements ChannelEPG.fragmentCommunicator {
    private Date selectedDate;
    private String channelId;
    private String channelTitle;
    private ViewPager pager;
    private boolean isTunable;

    @Override
    public void sendMessage(String name, Object msg) {
            if (msg != null) {
                    ChannelEPG item = (ChannelEPG) msg;
                    channelId = item.GetId();
                    channelTitle = item.GetTitle();
                    isTunable = item.GetTunable();
            } else {
                    pager.getAdapter().notifyDataSetChanged();
            }
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
            View v = inflater.inflate(R.layout.activity_channel_epgf, container, false);

            pager = (ViewPager) v.findViewById(R.id.viewPager);
            if (pager != null) {
                    pager.setAdapter(new myPagerAdapter(getChildFragmentManager()));
                    pager.setCurrentItem(1);
            }

            return v;
    }

    private class myPagerAdapter extends FragmentPagerAdapter {

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

            @Override
            public Fragment getItem(int pos) {
                    if (pos == 0) {
                            selectedDate = new Date();
                            selectedDate.setTime(selectedDate.getTime() - 24 * 3600 * 1000);
                            return ActivityChannelEPG.newInstance(selectedDate, channelId, channelTitle, isTunable);
                    } else if (pos == 1) {
                            selectedDate = new Date();
                            return ActivityChannelEPG.newInstance(selectedDate, channelId, channelTitle, isTunable);
                    } else if (pos == 2) {
                            selectedDate = new Date();
                            selectedDate.setTime(selectedDate.getTime() + 24 * 3600 * 1000);
                            return ActivityChannelEPG.newInstance(selectedDate, channelId, channelTitle, isTunable);
                    } else {
                            selectedDate.setTime(selectedDate.getTime() + 24 * 3600 * 1000); //THIS IS THE 82. rows
                            return ActivityChannelEPG.newInstance(selectedDate, channelId, channelTitle, isTunable);
                    }
            }

            @Override
            public int getCount() {
                    return 8;
            }

            public int getItemPosition(Object object) {
                    return POSITION_NONE;
            }
    }

}

`} else { selectedDate.setTime(selectedDate.getTime() + 24 * 3600 * 1000);` selectedDate is null here — Linh, Feb 16 '17 at 08:10
It is initiated when pos == 0,1,2. The code 99.999% works. I got this exception by firebase/crashreporting only at once. — RuntimeError, Feb 16 '17 at 08:19
@RuntimeError Because if/else is conditional statement. For example if position is 3. Your code won't run inside your if and else if statements and only will run inside else statement — Vygintas B, Feb 16 '17 at 08:36
@VygintasB The pager loads the page 1 and page 2 when created (pager.setCurrentItem(1);). The position 3 can only happens - in my mind - when there were position 1 or 2 before. — RuntimeError, Feb 16 '17 at 08:40
@RuntimeError well NPE was thrown for a reason and position 3 actually happened, not just in your mind — Vygintas B, Feb 16 '17 at 08:46

score 0 · Answer 1 · answered Feb 16 '17 at 08:16

0

You does not assign value to selected date, and this causes null pointer exception, you can see that you are doing this in all cases except one where npe is thrown

answered Feb 16 '17 at 08:16

Dmytro Grynets

923
11
29

I will try to change the code to selectedDate = new Date(); selectedDate.setTime(selectedDate.getTime() + 24 * 3600 * 1000 * (pos -1)); – RuntimeError Feb 16 '17 at 08:28

Why can a class member lost its value in Android?

1 Answers1