Apps Exception for ViewPager in NavigationView

[JMnemonic]

Hello,
I'm writing application with NavigationView and now I add to ViewPager on the layout for first Fragment.
Unfortunately, when i switch item in navigation and I come back to previous (with ViewPager) I have exception and application has been stopped.
Below part of code to change navigation item:

        switch (mNavItemId) {
            case R.id.drawer_item_1:
                getFragmentManager().beginTransaction().replace(R.id.content, mainSchedule)
                        .commit();
                break;
            case R.id.drawer_item_2:
                getFragmentManager().beginTransaction().replace(R.id.content, mFirstFragment)
                        .commit();
                break;
            case R.id.drawer_item_3:
                getFragmentManager().beginTransaction().replace(R.id.content, mSecondFragment)
                        .commit();
                break;
            case R.id.drawer_item_4:
                getFragmentManager().beginTransaction().replace(R.id.content, mThridFragment)
                        .commit();
                break;
            default:
                getFragmentManager().beginTransaction().replace(R.id.content, mainSchedule)
                        .commit();

Part in mainSchedule Fragment:

       View view = inflater.inflate(R.layout.main_schedule, container, false);

        mPager = (ViewPager) view.findViewById(R.id.viewpager);
        mPagerAdapter = new PageAdapters(getChildFragmentManager());
        mPagerAdapter.addFragments(new Test());
        mPager.setAdapter(mPagerAdapter);

        return view;

And part of class extends from FragmentStatePagerAdapter:

    List<Fragment> fragments;
    public PageAdapters(FragmentManager  fm) {
        super(fm);
        fragments = new ArrayList<Fragment>();
    }

    public void addFragments(Fragment fragment) {
        fragments.add(fragment);
    }

    @Override
    public Fragment getItem(int position) {

        return fragments.get(0);
    }

    @Override
    public int getCount() {
        return 2;
    }

Now I have :
java.lang.IllegalStateException: Fragment already added: Test
When I move Fragment Test to ViewPager class in method getItem(int position) I have:
java.lang.IllegalStateException: No activity

Can anybody explain me this and help me repair it?

 

[Deleted User]

Need to see the stack trace from your Logcat output.

 

[JMnemonic]

Okay, in attachments you'll find logs for both exceptions.