How to Update Fragment ViewPager

My approach to update fragments within the viewpager is to use the setTag() method for any instantiated view in the instantiateItem() method. So when you want to change the data or invalidate the view that you need, you can call the findViewWithTag() method on the ViewPager to retrieve the previously instantiated view and modify/use it as you want without having to delete/create a new view each time you want to update some value.

Imagine for example that you have 100 pages with 100 TextViews and you only want to update one value periodically. With the approaches explained before, this means you are removing and instantiating 100 TextViews on each update. It does not make sense…

You can see complete code here

In my adapter

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

import com.thedeveloperworldisyours.effectiveviewpager.fragments.FirstFragment;
import com.thedeveloperworldisyours.effectiveviewpager.fragments.SecondFragment;
import com.thedeveloperworldisyours.effectiveviewpager.fragments.ThirdFragment;

import java.util.HashMap;
import java.util.Map;

/**
* Created by javiergonzalezcabezas on 17/1/16.
*/
public class MyPagerAdapter extends FragmentPagerAdapter {
private static int NUM_ITEMS = 3;
private Map<Integer, String> mFragmentTags;
private FragmentManager mFragmentManager;

public MyPagerAdapter(FragmentManager fragmentManager) {
super(fragmentManager);
mFragmentManager = fragmentManager;
mFragmentTags = new HashMap<Integer, String>();
}

// Returns total number of pages
@Override
public int getCount() {
return NUM_ITEMS;
}

// Returns the fragment to display for that page
@Override
public Fragment getItem(int position) {
switch (position) {
case 0:
return FirstFragment.newInstance();
case 1:
return SecondFragment.newInstance();
case 2:
return ThirdFragment.newInstance();
default:
return null;
}
}

// Returns the page title for the top indicator
@Override
public CharSequence getPageTitle(int position) {
return "Page " + position;
}

@Override
public Object instantiateItem(ViewGroup container, int position) {
Object object = super.instantiateItem(container, position);
if (object instanceof Fragment) {
Fragment fragment = (Fragment) object;
String tag = fragment.getTag();
mFragmentTags.put(position, tag);
}
return object;
}

public Fragment getFragment(int position) {
Fragment fragment = null;
String tag = mFragmentTags.get(position);
if (tag != null) {
fragment = mFragmentManager.findFragmentByTag(tag);
}
return fragment;
}
}

And now in my activity:

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

import com.thedeveloperworldisyours.effectiveviewpager.adapters.MyPagerAdapter;

public class MainActivity extends AppCompatActivity implements ViewPager.OnPageChangeListener{

MyPagerAdapter mAdapterViewPager;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ViewPager viewPager = (ViewPager) findViewById(R.id.vpPager);
mAdapterViewPager = new MyPagerAdapter(getSupportFragmentManager());
viewPager.setAdapter(mAdapterViewPager);
viewPager.addOnPageChangeListener(this);
}

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

}

@Override
public void onPageSelected(int position) {

Fragment fragment = mAdapterViewPager.getFragment(position);
if (fragment != null) {
fragment.onResume();
}
}

@Override
public void onPageScrollStateChanged(int state) {

}
}

Finally in your Fragment, something like that:

public class YourFragment extends Fragment {

// newInstance constructor for creating fragment with arguments
public static YourFragment newInstance() {

return new YourFragment();
}

// Store instance variables based on arguments passed
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}

// Inflate the view for the fragment based on layout XML
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
return inflater.inflate(R.layout.fragment, container, false);
}

@Override
public void onResume() {
super.onResume();

//to refresh your view
refresh();

}
}

You can see complete code here

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