LifeCycle of Fragment With ViewPager

Question

07-02 01:24:00.530 15344-15344/com.example.dell.viewpagerlifecycle I/com.example.dell.viewpagerlifecycle.MainActivity: onCreate
07-02 01:24:00.534 15344-15344/com.example.dell.viewpagerlifecycle I/com.example.dell.viewpagerlifecycle.FragmentWithVP: onAttach
07-02 01:24:00.534 15344-15344/com.example.dell.viewpagerlifecycle I/com.example.dell.viewpagerlifecycle.FragmentWithVP: onCreate
07-02 01:24:00.558 15344-15344/com.example.dell.viewpagerlifecycle I/com.example.dell.viewpagerlifecycle.FragmentWithVP: onCreateView
07-02 01:24:00.558 15344-15344/com.example.dell.viewpagerlifecycle I/com.example.dell.viewpagerlifecycle.FragmentWithVP: onActivityCreated
07-02 01:24:00.558 15344-15344/com.example.dell.viewpagerlifecycle I/com.example.dell.viewpagerlifecycle.FragmentWithVP: onStart
07-02 01:24:00.558 15344-15344/com.example.dell.viewpagerlifecycle I/com.example.dell.viewpagerlifecycle.MainActivity: onStart
07-02 01:24:00.558 15344-15344/com.example.dell.viewpagerlifecycle I/com.example.dell.viewpagerlifecycle.MainActivity: onResume
07-02 01:24:00.558 15344-15344/com.example.dell.viewpagerlifecycle I/com.example.dell.viewpagerlifecycle.FragmentWithVP: onResume
07-02 01:24:00.603 15344-15344/com.example.dell.viewpagerlifecycle I/com.example.dell.viewpagerlifecycle.FragmentItem: : null onAttach
07-02 01:24:00.603 15344-15344/com.example.dell.viewpagerlifecycle I/com.example.dell.viewpagerlifecycle.FragmentItem: : 0 onCreate
07-02 01:24:00.603 15344-15344/com.example.dell.viewpagerlifecycle I/com.example.dell.viewpagerlifecycle.FragmentItem: : null onAttach
07-02 01:24:00.603 15344-15344/com.example.dell.viewpagerlifecycle I/com.example.dell.viewpagerlifecycle.FragmentItem: : 1 onCreate
07-02 01:24:00.607 15344-15344/com.example.dell.viewpagerlifecycle I/com.example.dell.viewpagerlifecycle.FragmentItem: : 1 onCreateView
07-02 01:24:00.607 15344-15344/com.example.dell.viewpagerlifecycle I/com.example.dell.viewpagerlifecycle.FragmentItem: : 1 onActivityCreated
07-02 01:24:00.608 15344-15344/com.example.dell.viewpagerlifecycle I/com.example.dell.viewpagerlifecycle.FragmentItem: : 0 onCreateView
07-02 01:24:00.608 15344-15344/com.example.dell.viewpagerlifecycle I/com.example.dell.viewpagerlifecycle.FragmentItem: : 0 onActivityCreated
07-02 01:24:00.608 15344-15344/com.example.dell.viewpagerlifecycle I/com.example.dell.viewpagerlifecycle.FragmentItem: : 0 onStart
07-02 01:24:00.608 15344-15344/com.example.dell.viewpagerlifecycle I/com.example.dell.viewpagerlifecycle.FragmentItem: : 0 onResume
07-02 01:24:00.608 15344-15344/com.example.dell.viewpagerlifecycle I/com.example.dell.viewpagerlifecycle.FragmentItem: : 1 onStart
07-02 01:24:00.608 15344-15344/com.example.dell.viewpagerlifecycle I/com.example.dell.viewpagerlifecycle.FragmentItem: : 1 onResume

ViewPagerAdapter is FragmentStatePagerAdapter

FragmentItem : Fragment that populates the viewpager FragmentWithVP : Fragment that has the viewPager. This fragment is contained in MainActivity

I thought, onCreateView of the viewPager fragments i.e. FragmentItem would be called When onCreateView of FragmentWithVP is called. But clearly it returns and its onStart and onResume are called.

1. So, How are the items of ViewPager populated?

2. Also how the onStart of FragmentWithVP called before MainActivity?

3. Also if a fragment contains nested fragemnts how are their lifecycle methods intertwined?

MainActivity.java

package com.example.dell.viewpagerlifecycle;

import android.content.Context;
import android.support.annotation.Nullable;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;

public class MainActivity extends AppCompatActivity
{

    static final String TAG = MainActivity.class.getCanonicalName() ;
    FragmentWithVP fragmentWithVP;
    @Override
    protected void onCreate(Bundle savedInstanceState)
    {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        FragmentManager fragmentManager = getSupportFragmentManager();

        fragmentWithVP = (FragmentWithVP) fragmentManager.findFragmentByTag("FragmentWithVP");

        if(fragmentWithVP == null)
        {
            fragmentWithVP = new FragmentWithVP();
            FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
            fragmentTransaction.replace(R.id.frame_layout,fragmentWithVP,"FragmentWithVP");
            fragmentTransaction.commit();
        }
        Log.i(TAG, "onCreate");
    }




    @Override
    public void onStart()
    {
        super.onStart();
        Log.i(TAG,"onStart");
    }

    @Override
    public void onResume()
    {
        super.onResume();
        Log.i(TAG,"onResume");
    }

    @Override
    public void onPause()
    {
        super.onPause();
        Log.i(TAG,"onPause");
    }

    @Override
    public void onStop()
    {
        super.onStop();
        Log.i(TAG,"onStop");
    }
}

FragmentWithVP.java

package com.example.dell.viewpagerlifecycle;


import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.support.v4.view.ViewPager;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;


/**
 * A simple {@link Fragment} subclass.
 */
public class FragmentWithVP extends Fragment
{

    static final String TAG = FragmentWithVP.class.getCanonicalName();
    MyAdapter myAdapter;

    public FragmentWithVP()
    {
        // Required empty public constructor
    }

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        Log.i(TAG,"onCreate");
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState)
    {


        // Inflate the layout for this fragment
        View view = inflater.inflate(R.layout.fragment_fragment_with_v, container, false);
        ViewPager viewPager = (ViewPager) view.findViewById(R.id.viewPager);
        myAdapter = new MyAdapter(getFragmentManager());
        viewPager.setAdapter(myAdapter);
        Log.i(TAG,"onCreateView");
        return view;
    }

    @Override
    public void onDestroyView()
    {
        super.onDestroyView();
        Log.i(TAG,"onDestoryView");
    }

    @Override
    public void onAttach(Context context)
    {
        super.onAttach(context);
        Log.i(TAG,"onAttach");
    }

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState)
    {
        super.onActivityCreated(savedInstanceState);
        Log.i(TAG,"onActivityCreated");
    }

    @Override
    public void onStart()
    {
        super.onStart();
        Log.i(TAG,"onStart");
    }
package com.example.dell.viewpagerlifecycle;


import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.support.v4.view.ViewPager;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;


/**
 * A simple {@link Fragment} subclass.
 */
public class FragmentWithVP extends Fragment
{

    static final String TAG = FragmentWithVP.class.getCanonicalName();
    MyAdapter myAdapter;

    public FragmentWithVP()
    {
        // Required empty public constructor
    }

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        Log.i(TAG,"onCreate");
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState)
    {


        // Inflate the layout for this fragment
        View view = inflater.inflate(R.layout.fragment_fragment_with_v, container, false);
        ViewPager viewPager = (ViewPager) view.findViewById(R.id.viewPager);
        myAdapter = new MyAdapter(getFragmentManager());
        viewPager.setAdapter(myAdapter);
        Log.i(TAG,"onCreateView");
        return view;
    }

    @Override
    public void onDestroyView()
    {
        super.onDestroyView();
        Log.i(TAG,"onDestoryView");
    }

    @Override
    public void onAttach(Context context)
    {
        super.onAttach(context);
        Log.i(TAG,"onAttach");
    }

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState)
    {
        super.onActivityCreated(savedInstanceState);
        Log.i(TAG,"onActivityCreated");
    }

    @Override
    public void onStart()
    {
        super.onStart();
        Log.i(TAG,"onStart");
    }

    @Override
    public void onResume()
    {
        super.onResume();
        Log.i(TAG,"onResume");
    }

    @Override
    public void onPause()
    {
        super.onPause();
        Log.i(TAG,"onPause");
    }

    @Override
    public void onStop()
    {
        super.onStop();
        Log.i(TAG,"onStop");
    }
}
@Override
public void onResume()
{
    super.onResume();
    Log.i(TAG,"onResume");
}

@Override
public void onPause()
{
    super.onPause();
    Log.i(TAG,"onPause");
}

@Override
public void onStop()
{
    super.onStop();
    Log.i(TAG,"onStop");
}
}

FragmentItem.java

package com.example.dell.viewpagerlifecycle;


import android.content.Context;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;


/**
 * A simple {@link Fragment} subclass.
 */
public class FragmentItem extends Fragment
{

    String label;
    static final String TAG = FragmentItem.class.getCanonicalName();
    public FragmentItem()
    {
        // Required empty public constructor
    }

    public static FragmentItem newInstance(String label)
    {

        Bundle args = new Bundle();
        args.putString("label", label);
        FragmentItem fragment = new FragmentItem();
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        label = getArguments().getString("label");
        Log.i(TAG,": "+label+" onCreate");
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState)
    {

        // Inflate the layout for this fragment
        View view = inflater.inflate(R.layout.fragment_fragment_item, container, false);
        TextView textView = (TextView) view.findViewById(R.id.textView);
        textView.setText(label);
        Log.i(TAG,": "+label+" onCreateView");
        return  view;

    }


    @Override
    public void onDestroy()
    {
        super.onDestroy();
        Log.i(TAG,": "+label+" onDestroy");
    }

    @Override
    public void onDestroyView()
    {
        super.onDestroyView();
        Log.i(TAG,": "+label+" onDestroyView");
    }

    @Override
    public void onAttach(Context context)
    {
        super.onAttach(context);
        Log.i(TAG,": "+label+" onAttach");
    }

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState)
    {
        super.onActivityCreated(savedInstanceState);
        Log.i(TAG,": "+label+" onActivityCreated");
    }

    @Override
    public void onStart()
    {
        super.onStart();
        Log.i(TAG,": "+label+" onStart");
    }

    @Override
    public void onResume()
    {
        super.onResume();
        Log.i(TAG,": "+label+" onResume");
    }

    @Override
    public void onPause()
    {
        super.onPause();
        Log.i(TAG,": "+label+" onPause");
    }

    @Override
    public void onStop()
    {
        super.onStop();
        Log.i(TAG,": "+label+" onStop");
    }

}

MyAdapter.java

package com.example.dell.viewpagerlifecycle;

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

/**
 * Created by dell on 2/7/16.
 */
public class MyAdapter extends FragmentStatePagerAdapter
{
    public MyAdapter(FragmentManager fm)
    {
        super(fm);
    }

    @Override
    public Fragment getItem(int position)
    {
        return new FragmentItem().newInstance(position+"");
    }

    @Override
    public int getCount()
    {
        return 200;
    }
}