How to handle network calls inside a Fragment

Question

I have the following situation:

I have an Activity that hosts a ViewPager, and I have 4 Fragments;

the ViewPager

Answer 1

@Andrew Carl provide good idea. I also use the similar approach in my projects. I think it's more generalized.

Create an interface:

public interface ViewPagerFragment {
    void onSelected();

    void onDeselected();
}

And this common helper:

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.view.ViewPager;

public class ViewPagerHelper implements ViewPager.OnPageChangeListener {
    private final FragmentManager mFragmentManager;
    private final ViewPager mViewPager;
    private int mSelectedPage;

    public ViewPagerHelper(FragmentManager fragmentManager, ViewPager viewPager) {
        mFragmentManager = fragmentManager;
        mViewPager = viewPager;
        mSelectedPage = -1;
    }

    @Override
    public void onPageSelected(int position) {
        Fragment previous = findViewPagerChildFragment(mFragmentManager, mViewPager, mSelectedPage);
        if (previous instanceof ViewPagerFragment) {
            ((ViewPagerFragment) previous).onDeselected();
        }

        Fragment current = findViewPagerChildFragment(mFragmentManager, mViewPager, position);
        if (current instanceof ViewPagerFragment) {
            ((ViewPagerFragment) current).onSelected();
        }

        mSelectedPage = position;
    }

    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
        // empty
    }

    @Override
    public void onPageScrollStateChanged(int state) {
        // empty
    }

    public static Fragment findViewPagerChildFragment(FragmentManager manager, ViewPager pager, int position) {
        if (pager == null) {
            return null;
        }

        String tag = "android:switcher:" + pager.getId() + ":" + position;
        return manager.findFragmentByTag(tag);
    }
}

Now you may use them for any purpose:

Fragment:

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import android.widget.Toast;

public class MyFragment extends Fragment implements ViewPagerFragment {
    private boolean mSelected;

    public static MyFragment newInstance(int position) {
        Bundle args = new Bundle();
        args.putInt("position", position);

        MyFragment result = new MyFragment();
        result.setArguments(args);
        return result;
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        TextView result = new TextView(inflater.getContext());
        result.setText("Position: " + getPosition());
        return result;
    }

    private int getPosition() {
        return getArguments().getInt("position");
    }

    @Override
    public void onSelected() {
        mSelected = true;
        start();
    }

    @Override
    public void onDeselected() {
        mSelected = false;
    }

    private void start() {
        final Handler handler = new Handler();
        handler.postDelayed(new Runnable() {
            @Override
            public void run() {
                Activity activity = getActivity();
                if (activity == null) {
                    return;
                }

                if (!mSelected) {
                    Toast.makeText(activity, "Fragment #" + getPosition() + " stopped", Toast.LENGTH_SHORT).show();
                    return;
                }

                TextView textView = (TextView) activity.findViewById(R.id.text);
                if (textView != null) {
                    textView.setText("Fragment #" + getPosition() + " works: " + System.nanoTime() % 10000);
                }

                handler.postDelayed(this, 150);
            }
        }, 150);
    }
}

Activity:

import android.os.Bundle;
import android.support.v4.view.ViewPager;
import android.support.v7.app.ActionBarActivity;

public class MainActivity extends ActionBarActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        ViewPager viewPager = (ViewPager) findViewById(R.id.view_pager);
        viewPager.setOnPageChangeListener(new ViewPagerHelper(getSupportFragmentManager(), viewPager));
        viewPager.setAdapter(new MyAdapter(getSupportFragmentManager()));
    }
}

Adapter:

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

public class MyAdapter extends FragmentPagerAdapter {
    public MyAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int position) {
        return MyFragment.newInstance(position);
    }

    @Override
    public int getCount() {
        return 42;
    }
}

Check complete demo on github.