프로젝트를 처음 만들때 설정하는 내비게이션 드로어로 메뉴들을 만들어 주고 그 메뉴중 두번째 메뉴를 누르면 웹뷰를 바로 띄우고 싶습니다. 인텐트로 웹뷰를 띄우긴 했지만, 기존에 설정된 툴바가 없어져 새로 띄워진 웹뷰에서는 내비게이션 드로어를 사용할 수 없게 됩니다.

MainActivity.java

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





    MainFragment fragment = new MainFragment();
    android.support.v4.app.FragmentTransaction fragmentTransaction =    getSupportFragmentManager().beginTransaction();

    fragmentTransaction.replace(R.id.fragment_container, fragment); 
    fragmentTransaction.commit();


    toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show();
        }
    });


    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) findViewById(R.id.nav_view); 
    //How to change elements in the header programatically
    View headerView = navigationView.getHeaderView(0);
    TextView emailText = (TextView) headerView.findViewById(R.id.email);
    emailText.setText("ghkvud5638@naver.com");

    navigationView.setNavigationItemSelectedListener(this); 


}


public void onButton1Clicked(View v){
    Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse("http://m.naver.com"));
    startActivity(intent);

}

@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();

    if (id == R.id.action_settings) {
        return true;
    } else if(id ==R.id.action_search){

        return true;
    }

    return super.onOptionsItemSelected(item);
}



@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
    int id = item.getItemId();

    if (id == R.id.sideMenu1) {
        //Set the fragment initially
        MainFragment fragment = new MainFragment();
        android.support.v4.app.FragmentTransaction fragmentTransaction =
                getSupportFragmentManager().beginTransaction();
        fragmentTransaction.replace(R.id.fragment_container, fragment);
        fragmentTransaction.commit();
    }        else if (id == R.id.sideMenu2) {

         Intent intent = new Intent(getApplication(), webViewActivity.class);
         startActivity(intent);


    } else if (id == R.id.sideMenu3) {

        Menu3Fragment fragment = new Menu3Fragment();   
        android.support.v4.app.FragmentTransaction fragmentTransaction =
                getSupportFragmentManager().beginTransaction();
        fragmentTransaction.replace(R.id.fragment_container, fragment);
        fragmentTransaction.commit();



    } else if (id == R.id.sideMenu4) {

    } else if (id == R.id.sideMenu5) {

    } else if (id == R.id.sideMenu6) {

    }

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

}

}

activity_web_view.xml

<WebView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/webView1"
    ></WebView>

webViewActivity.java

public class webViewActivity extends AppCompatActivity {

WebView webView1;
Toolbar toolbar;

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




    webView1 = (WebView) findViewById(R.id.webView1);
    WebSettings webSettings = webView1.getSettings();

    webSettings.setJavaScriptEnabled(true);

    webView1.loadUrl("http://m.naver.com");






}

}