tabstrip with fragment and viewpager problem

import android.support.design.widget.Snackbar;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.app.FragmentStatePagerAdapter;
import android.support.v4.app.FragmentTransaction;
import android.support.v4.app.ListFragment;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.view.ViewGroup;
import android.widget.FrameLayout;
import android.widget.Toast;

import com.gigamole.navigationtabstrip.NavigationTabStrip;

public class MainActivity extends AppCompatActivity {

private NavigationTabStrip mCenterNavigationTabStrip;
private FrameLayout frameLayout;
private ViewPager mViewPager;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
getSupportActionBar().setDisplayShowHomeEnabled(true);

mCenterNavigationTabStrip = (NavigationTabStrip) findViewById(R.id.nts_center);
mViewPager = (ViewPager) findViewById(R.id.vp);

toolbar.setTitleTextColor(G.context.getResources().getColor(R.color.item));
frameLayout = (FrameLayout) findViewById(R.id.farmlayout);

setUI();

mCenterNavigationTabStrip.setViewPager(mViewPager);

mCenterNavigationTabStrip.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

}

@Override
public void onPageSelected(int position) {
// Toast.makeText(G.context, "positon =" + position, Toast.LENGTH_SHORT).show();
mViewPager.setCurrentItem(position);
// Toast.makeText(G.context, "positon =" + mViewPager.getCurrentItem(), Toast.LENGTH_SHORT).show();
}

@Override
public void onPageScrollStateChanged(int state) {

}
});

mCenterNavigationTabStrip.setOnTabStripSelectedIndexListener(new NavigationTabStrip.OnTabStripSelectedIndexListener() {
@Override
public void onStartTabSelected(String title, int index) {
mViewPager.setCurrentItem(index);
Toast.makeText(G.context, "viewpager =" + mViewPager.getCurrentItem() + "index " + index , Toast.LENGTH_SHORT).show();
}

@Override
public void onEndTabSelected(String title, int index) {

}
});
}

@Override
public boolean onSupportNavigateUp() {
onBackPressed();
return true;
}

private void setUI() {
mViewPager.setAdapter(new FragmentPagerAdapter(getSupportFragmentManager()) {
@Override
public Fragment getItem(int position) {
switch (position) {
case 0:
return new loginFragment();
case 1:
return new signupFragment();
default:
return null;
}
}

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

}
}