Fragment Implementation

BaseFragmet.java

import android.app.Fragment;
import android.content.Context;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import com.retrofitrealm.controllers.MainActivityInterface;

import butterknife.ButterKnife;
import butterknife.Unbinder;

/**
 * Created by Phil on 10/01/2017.
 */

public abstract class BaseFragment extends Fragment {

    private Unbinder baseUnbinder;

    public MainActivityInterface mainActivityInterface;
    public abstract int getLayout();

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

    @Override
    public void onDestroyView() {
        super.onDestroyView();
        if(null != baseUnbinder)
            baseUnbinder.unbind();
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        mainActivityInterface = (MainActivityInterface) context;
    }
}

ImagesFragment.java

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import com.retrofitrealm.R;
import com.retrofitrealm.fragments.assets.BaseFragment;

import butterknife.BindView;

/**
 * Created by Phil on 10/01/2017.
 */

public class ImagesFragment extends BaseFragment {
    
    private static String TV_VALUE = "tvValue";

    @BindView(R.id.tvTitle)
    TextView tvTitle;

    public static BaseFragment newInstance(String tvValue) {
        ImagesFragment imagesFragment = new ImagesFragment();
        Bundle arg0 = new Bundle();
        arg0.putString(TV_VALUE, tvValue);
        imagesFragment.setArguments(arg0);
        return imagesFragment;
    }

    @Override
    public int getLayout() {
        return R.layout.images_fragment;
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = super.onCreateView(inflater, container, savedInstanceState);
        tvTitle.setText(getArguments().getString(TV_VALUE));
        return view;
    }
}

MainActivity.java

import android.app.FragmentManager;
import android.app.FragmentTransaction;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

import com.retrofitrealm.R;
import com.retrofitrealm.controllers.MainActivityInterface;
import com.retrofitrealm.fragments.ImagesFragment;
import com.retrofitrealm.fragments.assets.BaseFragment;

public class MainActivity extends AppCompatActivity implements MainActivityInterface {

    private FragmentManager fragManager;
    private FragmentTransaction fragTransaction;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        setupFragmentManager();
        loadImagesFragment("This is a fragment");
    }

    @Override
    public void loadImagesFragment(String tvValue) {
        switchFragment(ImagesFragment.newInstance(tvValue), "Images Fragment");
    }

    @Override
    public void goBack() {
        onBackPressed();
    }

    @Override
    public void onBackPressed() {
        if (this.fragManager.getBackStackEntryCount() != 1) {
            fragManager.popBackStack();
            if (this.fragManager.getBackStackEntryCount() == 0) {
                super.onBackPressed();
            }
        } else {
            finish();
        }

    }

    private void switchFragment(BaseFragment fragment, String fragmentName) {
        this.fragTransaction = getBaseFragmentManager().beginTransaction();
        this.fragTransaction.replace(R.id.flMainContainer, fragment, fragmentName);
        this.fragTransaction.addToBackStack(fragmentName);
        this.fragTransaction.commit();
    }

    private FragmentManager getBaseFragmentManager() {
        if (null == this.fragManager) {
            throw new IllegalStateException(MainActivity.class.getSimpleName() +
                    " is not initialized, call setupFragmentManager(...) first");
        }
        return this.fragManager;
    }

    private void setupFragmentManager() {
        fragManager = getFragmentManager();
    }
}

MainActivityInterface.java

/**
 * Created by Phil on 10/01/2017.
 */

public interface MainActivityInterface {
    void loadImagesFragment(String tvValue);
    void goBack();
}