Main activity (code)

[MimaMax]

package com.example.dom.primehousemodern;

import android.app.Application;
import android.content.Intent;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.app.FragmentTransaction;
import android.view.View;
import android.support.design.widget.NavigationView;
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 android.webkit.WebView;
import android.webkit.WebViewClient;

import com.example.dom.primehousemodern.fragments.FragmentFavorites;
import com.example.dom.primehousemodern.fragments.FragmentLearn;
import com.example.dom.primehousemodern.fragments.FragmentTest;
import com.example.dom.primehousemodern.fragments.FragmentWeb;

public class MainActivity extends AppCompatActivity


        implements NavigationView.OnNavigationItemSelectedListener {

    FragmentLearn flearn;
    FragmentTest ftest;
    FragmentFavorites ffavorites;
    FragmentWeb fweb;
    

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

        // toolbar
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        getSupportActionBar().setDisplayShowHomeEnabled(true);


        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.addDrawerListener(toggle);
        toggle.syncState();

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


        flearn = new FragmentLearn();
        ftest = new FragmentTest();
        ffavorites = new FragmentFavorites();
        fweb = new FragmentWeb();



        FragmentTransaction ftrans = getFragmentManager().beginTransaction();
        ftrans.replace(R.id.container, flearn);
        setTitle("Обучение");
        ftrans.commit();

    }



    //Объявление Глобальной переменной

    public static class Global {
        public static int rightAnswers;
    }

    //Конец объявления

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


    @Override
    public void onBackPressed() {
        if (getFragmentManager().getBackStackEntryCount() > 0 ){
            getFragmentManager().popBackStack();
        } else {
            super.onBackPressed();
        }
    }

  /*  @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.main, 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.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @SuppressWarnings("StatementWithEmptyBody")
    @Override
    public boolean onNavigationItemSelected(MenuItem item) {
        // Handle navigation view item clicks here.
        int id = item.getItemId();

        FragmentTransaction ftrans = getFragmentManager().beginTransaction();

        if (id == R.id.nav_camera) {
            ftrans.replace(R.id.container, flearn);
            setTitle("Обучение");
        } else if (id == R.id.nav_gallery) {
            ftrans.replace(R.id.container, ftest);
            setTitle("Тест");
        } else if (id == R.id.nav_slideshow) {
            ftrans.replace(R.id.container, ffavorites);
            setTitle("Избранное");
        } else if (id == R.id.nav_manage) {
            ftrans.replace(R.id.container, fweb);
            setTitle("Сайт");
        } ftrans.addToBackStack(null).commit();

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

}