在片段中显示和使用“后退”按钮

Question

 public class NewFrag extends Fragment{ @Override public void onCreate(@Nullable Bundle savedInstanceState) { super.onCreate(savedInstanceState); ((AppCompatActivity)getActivity()).getSupportActionBar().setDisplayHomeAsUpEnabled(true); setHasOptionsMenu(true); } @Nullable @Override public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) { return inflater.inflate(R.layout.newfrag, container, false); } } 

 public class PrimaryFragment extends Fragment { Button btn1; @Nullable @Override public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) { return inflater.inflate(R.layout.primary, container, false); } @Override public void onViewCreated(View view, @Nullable Bundle savedInstanceState) { super.onViewCreated(view, savedInstanceState); btn1 = (Button)view.findViewById(R.id.btn1); btn1.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { Fragment var1 = new NewFrag(); ((MainActivity)getActivity()).replaceFragment(var1); } }); } } 

 public class TabFragment extends Fragment { public static TabLayout tabLayout; public static ViewPager viewPager; public static int int_items = 2 ; @Nullable @Override public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) { return inflater.inflate(R.layout.tab_layout, container, false); } @Override public void onViewCreated(View view, @Nullable Bundle savedInstanceState) { super.onViewCreated(view, savedInstanceState); tabLayout = (TabLayout) view.findViewById(R.id.tabs); viewPager = (ViewPager) view.findViewById(R.id.viewpager); viewPager.setAdapter(new MyAdapter(getChildFragmentManager())); tabLayout.post(new Runnable() { @Override public void run() { tabLayout.setupWithViewPager(viewPager); } }); } class MyAdapter extends FragmentPagerAdapter { public MyAdapter(FragmentManager fm) { super(fm); } /** * Return fragment with respect to Position . */ @Override public Fragment getItem(int position) { switch (position){ case 0 : return new PrimaryFragment(); case 1 : return new SocialFragment(); } return null; } @Override public int getCount() { return int_items; } /** * This method returns the title of the tab according to the position. */ @Override public CharSequence getPageTitle(int position) { switch (position){ case 0 : return "Primary"; case 1 : return "Social"; } return null; } } } 

 public class MainActivity extends AppCompatActivity{ DrawerLayout mDrawerLayout; NavigationView mNavigationView; ActionBarDrawerToggle mDrawerToggle; FragmentManager mFragmentManager; FragmentTransaction mFragmentTransaction; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); /** *Setup the DrawerLayout and NavigationView */ mDrawerLayout = (DrawerLayout) findViewById(R.id.drawerLayout); mNavigationView = (NavigationView) findViewById(R.id.shitstuff) ; /** * Lets inflate the very first fragment * Here , we are inflating the TabFragment as the first Fragment */ mFragmentManager = getSupportFragmentManager(); mFragmentTransaction = mFragmentManager.beginTransaction(); mFragmentTransaction.replace(R.id.containerView,new TabFragment()).addToBackStack(null).commit(); /** * Setup click events on the Navigation View Items. */ mNavigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() { @Override public boolean onNavigationItemSelected(MenuItem menuItem) { mDrawerLayout.closeDrawers(); if (menuItem.getItemId() == R.id.nav_item_inbox) { FragmentTransaction fragmentTransaction = mFragmentManager.beginTransaction(); fragmentTransaction.replace(R.id.containerView,new NavOne()).addToBackStack(null).commit(); } if (menuItem.getItemId() == R.id.nav_item_sent) { FragmentTransaction xfragmentTransaction = mFragmentManager.beginTransaction(); xfragmentTransaction.replace(R.id.containerView,new NavTwo()).addToBackStack(null).commit(); } return false; } }); /** * Setup Drawer Toggle of the Toolbar */ Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); mDrawerToggle = new ActionBarDrawerToggle(this,mDrawerLayout, toolbar,R.string.app_name, R.string.app_name); mDrawerLayout.setDrawerListener(mDrawerToggle); mDrawerToggle.syncState(); } public void replaceFragment(Fragment fragment){ FragmentTransaction t = getSupportFragmentManager().beginTransaction(); t.replace(R.id.containerView, fragment).addToBackStack(null); t.commit(); } public void showArrow(){ mDrawerToggle.setDrawerIndicatorEnabled(false); //getSupportActionBar().setDisplayHomeAsUpEnabled(true); } @Override public boolean onOptionsItemSelected(MenuItem item) { switch (item.getItemId()) { case android.R.id.home: onBackPressed(); break; default: break; } return super.onOptionsItemSelected(item); } } 

This topic may look very old and there might be many answers but my situation is very unique. I have to implement Navigation Drawer and TabLayout in MainActivity. So I used this tutorial for that. It uses FrameLayout + Navigation in MainActivity and attaches a fragment with the FrameLayout. This fragment has TabLayout. Now I have a button in one of the Tab's fragment which will open another fragment. I want to display back arrow button in this new fragment. I disabled drawertoggle but unable to show back button. But my app crashes with a NullPointerException. Is there any other way to show the arrow button and also use it to go to previous fragment?

Answer 1

Before you call commit(), however, you might want to call addToBackStack(), in order to add the transaction to a back stack of fragment transactions. This back stack is managed by the activity and allows the user to return to the previous fragment state, by pressing the Back button.

Example:

FragmentTransaction tx = fragmentManager.beginTransation();
tx.replace( R.id.fragment, new MyFragment() ).addToBackStack( "tag" ).commit();

My solution:

main menu xml:

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:app="http://schemas.android.com/apk/res-auto">
<item android:id="@+id/action_settings"
      android:title="@string/action_settings"
      android:orderInCategory="100"
      app:showAsAction="never"/>

<item android:id="@+id/my_back_arrowID"
      android:icon="@drawable/arrow_left"
      android:visible="false"
      app:showAsAction="ifRoom">


</item>

MainActivity:

 @Override
public boolean onCreateOptionsMenu(Menu menu) {

    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {

    int id = item.getItemId();


    if (id == R.id.action_settings) {
        Toast.makeText(MainActivity.this, "settings", Toast.LENGTH_SHORT).show();
    } else if (id == R.id.my_back_arrowID) {

        onBackPressed();


    }


    return super.onOptionsItemSelected(item);
}

Your fragment where you want the back arrow to be visible:

 @Override
public void onPrepareOptionsMenu(Menu menu) {

    menu.findItem(R.id.my_back_arrowID).setVisible(true);


    super.onPrepareOptionsMenu(menu);
}