在transaction.com发布之前调用片段的onCreate

Question

I have multiple fragments in viewpager. Fragment A, Fragment B , Fragment C and Fragment D. Fragment C is replacing itself with another fragment which extends list fragment. I want to replace the fragment when only Fragment C is visible. because there is some background AsyncTask being performed which should be done when the fragment C is selected. I have replaced the fragment which works fine. But the problem is that its state is being saved. Because whenever Fragment C's neighbor is called The fragment replaced inside Fragment C is also called automatically

I have implemented all code. I Just dont want to call the replacing fragment when Fragment C's neighbor Fragment is called

public class VendorsListFragment extends Fragment {

private static final String TAG = VendorsActivity.class.getSimpleName();

@BindView(R.id.layoutAdViewBottomVendorActivity)
AdView mAdView;
View view;
boolean isLaunched= false;
boolean isRejected= false;

public VendorsListFragment() {
}

@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    view = inflater.inflate(R.layout.activity_vendors, container, false);
    ButterKnife.bind(this, view);
    return view;
}

public void callNewFragment() {

        FragmentManager manager = getChildFragmentManager();
        FragmentTransaction ft = manager.beginTransaction();
        VendorFragment vendorFragment = new VendorFragment();

        ft.remove(vendorFragment);
        ft.replace(R.id.vendorFragmentContainer, new VendorFragment());
        //container is the ViewGroup of current fragment
        ft.addToBackStack(null);
        ft.commit();
        ft.commitAllowingStateLoss();
}
}

Activity which has ViewPager has following code

public class NetworkToolsActivity extends AppCompatActivity  {

TabLayout tabHost;
public ViewPager pager;
ViewPagerAdapter adapter;
private Resources res;
int tabPosition;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    initializeMainContext(this);

    setContentView(R.layout.activity_network_tools);
    res = this.getResources();
    Intent mIntent = getIntent();
    int selectedTab = mIntent.getIntExtra("tabPosition", 0);

    Toolbar toolbar = (Toolbar) this.findViewById(R.id.toolbar);
    toolbar.setTitleTextColor(Color.WHITE);
    setSupportActionBar(toolbar);
    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    getSupportActionBar().setDisplayShowHomeEnabled(true);
    this.setSupportActionBar(toolbar);
    tabHost = findViewById(R.id.tabHost);
    pager = (ViewPager) this.findViewById(R.id.pager );
    adapter = new ViewPagerAdapter(getSupportFragmentManager());
    pager.setAdapter(adapter);

    final int pageMargin = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 4, getResources()
            .getDisplayMetrics());
    pager.setPageMargin(pageMargin);

    tabHost.setupWithViewPager(pager);
    pager.setCurrentItem(selectedTab);
    pager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

        }

        @Override
        public void onPageSelected(int position) {
            if (position==6){
                VendorsListFragment frag  = (VendorsListFragment)adapter.getItem(position);
                frag.callNewFragment();
            }
        }

        @Override
        public void onPageScrollStateChanged(int state) {

        }
    });

} 
}

ViewPager Adapter Class

public class ViewPagerAdapter extends FragmentStatePagerAdapter {
public ViewPagerAdapter(FragmentManager fm) {
    super(fm);
}

@Override
public Fragment getItem(int position) {
    Fragment frag = null;
    switch (position) {
        case 0:
            frag = new SpeedTestFragment();
            break;
        case 1:
            frag = new LanScanFragment();
            break;
        case 2:
            frag = new IpToolFragment();
            break;
        case 3:
            frag = new RouterFinderFragment();
            break;
        case 4:
            frag = new NetworkInformationFragment();
            break;
        case 5:
            frag = new ChannelRatingFragment();
            break;

        case 6:
            frag = new VendorsListFragment();
            break;
        case 7:
            frag = new AccessPointsFragment();
            break;
        case 8:
            frag = new ChannelRatingFragment();
            break;
        case 9:
            frag = new ChannelGraphFragment();
            break;
        case 10:
            frag = new TimeGraphFragment();
            break;

    }

    return frag;
}

@Override
public int getCount() {
    return 11;
}

@Nullable
@Override
public CharSequence getPageTitle(int position) {
    CharSequence sequence = null;
    switch (position) {
        case 0:
            sequence = "Speed Test";
            break;
        case 1:
            sequence = "Lan Scan";
            break;
        case 2:
            sequence = "Ip Tools";
            break;
        case 3:
            sequence = "Router Finder";
            break;
        case 4:
            sequence = "Network Information";
            break;
        case 5:
            sequence = "Available Channels";
            break;
        case 6:
            sequence = "Vendors";
            break;
        case 7:
            sequence = "Access Point";
            break;
        case 8:
            sequence = "Channel Rating";
            break;
        case 9:
            sequence = "Channel Graph";
            break;
        case 10:
            sequence = "Time Graph";
            break;

    }
    return sequence;
}

}

Answer 1

You need to get ViewPager 's CurrentItem to see if it is at 3rd position.

if (getActivity() != null && ((YourActivity)getActivity()).viewPager.getCurrentItem() == 2){
    // Call ReplaceFragment here
}

inside Activity you need to implement ViewPager OnPageChangeListener . It has onPageSelected method which gives you the position of the page. It will always get called whenever you change your fragment.

EDIT

inside onPageSelected

if (position == 2){
   YourFragment frag  = (YourFragment)adapter.getItem(position)
   frag.callNewFragment()
}

EDIT 2

import android.os.Parcelable;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentStatePagerAdapter;

import java.util.ArrayList;
import java.util.List;

public class ViewPagerAdapter extends FragmentStatePagerAdapter {
private final List<Fragment> mFragmentList = new ArrayList<>();
private final List<String> mFragmentTitleList = new ArrayList<>();

public ViewPagerAdapter(FragmentManager fm) {
    super(fm);
    mFragmentList.clear();
    mFragmentTitleList.clear();
}

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

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

public void addFragment(Fragment fragment, String title) {
    mFragmentList.add(fragment);
    mFragmentTitleList.add(title);
}

@Override
public Parcelable saveState() {
    return null;
}

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

and then add fragment like below:

adapter.addFragment(new SpeedTestFragment(), "Speed Test");

// add all 11 like above
adapter.notifyDataSetChanged();