ตัวอย่างการ Detect Current Fragment เพื่อซ่อน View บางอย่างใน Activity

MainActivity.java

package com.akexorcist.fragmenttest;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.support.v7.app.ActionBarActivity;
import android.view.View;
import android.widget.Button;
import android.widget.LinearLayout;


public class MainActivity extends ActionBarActivity implements View.OnClickListener, FragmentManager.OnBackStackChangedListener {
    private Button btnP1, btnP2, btnP3, btnP4;
    private LinearLayout layoutTitle;
    private FragmentManager fragmentManager;

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

        layoutTitle = (LinearLayout) findViewById(R.id.layout_title);

        btnP1 = (Button) findViewById(R.id.btn_p1);
        btnP2 = (Button) findViewById(R.id.btn_p2);
        btnP3 = (Button) findViewById(R.id.btn_p3);
        btnP4 = (Button) findViewById(R.id.btn_p4);

        btnP1.setOnClickListener(this);
        btnP2.setOnClickListener(this);
        btnP3.setOnClickListener(this);
        btnP4.setOnClickListener(this);

        fragmentManager = getSupportFragmentManager();
        fragmentManager.addOnBackStackChangedListener(this);
    }

    @Override
    public void onClick(View v) {
        int id = v.getId();
        switch (id) {
            case R.id.btn_p1 :
                replaceFragment(OneFragment.getInstance());
                break;
            case R.id.btn_p2 :
                replaceFragment(TwoFragment.getInstance());
                break;
            case R.id.btn_p3 :
                replaceFragment(ThreeFragment.getInstance());
                break;
            case R.id.btn_p4 :
                replaceFragment(FourFragment.getInstance());
                break;
        }
    }

    @Override
    public void onBackStackChanged() {
        Fragment fragment = getActiveFragment();
        if(fragment != null) {
            String fragmentName = fragment.getClass().getSimpleName();
            if (OneFragment.class.getSimpleName().equals(fragmentName)) {
                layoutTitle.setVisibility(View.VISIBLE);
            } else if (TwoFragment.class.getSimpleName().equals(fragmentName)) {
                layoutTitle.setVisibility(View.VISIBLE);
            } else if (ThreeFragment.class.getSimpleName().equals(fragmentName)) {
                layoutTitle.setVisibility(View.GONE);
            } else if (FourFragment.class.getSimpleName().equals(fragmentName)) {
                layoutTitle.setVisibility(View.VISIBLE);
            }
        }
    }

    private void replaceFragment(Fragment fragment) {
        FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
        transaction.replace(R.id.fragment_container, fragment, fragment.getClass().getSimpleName());
        transaction.addToBackStack(fragment.getClass().getSimpleName());
        transaction.commit();
    }

    private Fragment getActiveFragment() {
        if (fragmentManager.getBackStackEntryCount() == 0) {
            return null;
        }
        String tag = fragmentManager.getBackStackEntryAt(fragmentManager.getBackStackEntryCount() - 1).getName();
        return fragmentManager.findFragmentByTag(tag);
    }
}