On pressing back button app closes while using fragments in navigation drawer in single activity

Question

I am having trouble with fragments in navigation drawer. Currently when i am pressing back button my app closes , as i am using single activity and multiple fragments . I want to maintain a stack , so on switching fragments, after pressing back button , it should move to previous fragments Here is my code

package rock.ori_mydiary;

import android.content.Intent;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.design.widget.NavigationView;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentTransaction;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;

import com.google.android.gms.auth.api.Auth;
import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.api.GoogleApiClient;
import com.google.android.gms.common.api.ResultCallback;
import com.google.android.gms.common.api.Status;

public class Announcement extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener, GoogleApiClient.OnConnectionFailedListener {

    private GoogleApiClient mGoogleApiClient;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_announcement);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        toolbar.setTitle("Announcement");
        setSupportActionBar(toolbar);
        mGoogleApiClient = new GoogleApiClient.Builder(this)
                .enableAutoManage(this /* FragmentActivity */, this /* OnConnectionFailedListener */)
                .addApi(Auth.GOOGLE_SIGN_IN_API)
                .build();
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.setDrawerListener(toggle);
        toggle.syncState();

        NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);
        displaySelectedScreen(R.id.menu_announce);
    }

    @Override
    public void onBackPressed() {
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            super.onBackPressed();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.announcement, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.logout) {
            Auth.GoogleSignInApi.signOut(mGoogleApiClient).setResultCallback(
                    new ResultCallback<Status>() {
                        @Override
                        public void onResult(Status status) {


                        }
                    });
            Intent intent = new Intent(this,LoginActivity.class);
            intent.putExtra("keylog","yes");

            startActivity(intent);
            finish();
        }

        return super.onOptionsItemSelected(item);
    }

    @SuppressWarnings("StatementWithEmptyBody")
    @Override
    public boolean onNavigationItemSelected(MenuItem item) {
        // Handle navigation view item clicks here.
        //calling the method displayselectedscreen and passing the id of selected menu
        displaySelectedScreen(item.getItemId());

        return true;
    }
    private void displaySelectedScreen(int itemId) {

        //creating fragment object
        Fragment fragment = null;

        //initializing the fragment object which is selected
        switch (itemId) {
            case R.id.menu_assignment:
                fragment = new fragment_assignment();
                break;
            case R.id.menu_announce:
                fragment = new fragment_announcement();
                break;
            case R.id.menu_notice:
                fragment = new fragment_notice();
                break;

            case R.id.menu_attendance:
                fragment = new fragment_attendance();
                break;
            case R.id.menu_event_marks:
                fragment = new fragment_event_marks();
                break;
            case R.id.menu_eresource:
                fragment = new fragment_eresource();
                break;
            case R.id.menu_time_table:
                fragment = new fragment_time_table();
                break;
        }

        //replacing the fragment
        if (fragment != null) {
            FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
            ft.replace(R.id.content_frame, fragment);
            ft.commit();
        }

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);
    }

    @Override
    protected void onStart() {
        super.onStart();
        mGoogleApiClient.connect();
    }
    @Override
    public void onConnectionFailed(@NonNull ConnectionResult connectionResult) {

    }
}

Answer 1

You have to manage the Fragment Back Stack as below:

FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
            ft.replace(R.id.content_frame, fragment);
            ft.addToBackStack(null);
            ft.commit();

Now when you press back button each time your previous fragment in stack is called.

Answer 2

Set previous id list and use that list for navigation on back press.

ArrayList<Integer> previousId_List = new ArrayList<Integer>();

@Override
    public void onBackPressed() {
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            //get previous id from previousId_List
            displaySelectedScreen(previousId);
        }
    }

 @SuppressWarnings("StatementWithEmptyBody")
    @Override
    public boolean onNavigationItemSelected(MenuItem item) {
        // Handle navigation view item clicks here.
        //calling the method displayselectedscreen and passing the id of selected menu
        displaySelectedScreen(item.getItemId());
        //set id in previousId_List 
        previousId_List.add(item.getItemId());
        return true;
    }