NPE at adding Drawer Listener

Question

I am currently trying to program a small app, now I am trying to use a Navigation Drawer in my app. This does not work with the reason that I get a NPE at drawer.addDrawerListener(toggle);. Everything else seems to be fine as far as I can say and the app worked correctly till adding the drawer. Thx in advance.

import android.content.Intent;
import android.content.res.Configuration;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.Bundle;
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.widget.TextView;
import de.nocompany.gotthold.gw2companion.Tools.GwApiAccess;

public class MainActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener {

    private DrawerLayout drawer;
    private Toolbar toolbar;
    private ActionBarDrawerToggle toggle;
    private NavigationView navigationView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        toolbar = (Toolbar) findViewById(R.id.toolbar);
        drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        navigationView = (NavigationView) findViewById(R.id.nav_view);
        setSupportActionBar(toolbar);
        setContentView(R.layout.activity_main);

        toggle = new ActionBarDrawerToggle(this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close) {

            /** Called when a drawer has settled in a completely closed state. */
            public void onDrawerClosed(View view) {
                super.onDrawerClosed(view);
                //getActionBar().setTitle(mTitle);
                invalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()
            }

            /** Called when a drawer has settled in a completely open state. */
            public void onDrawerOpened(View drawerView) {
                super.onDrawerOpened(drawerView);
                //getActionBar().setTitle(mDrawerTitle);
                invalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()
            }
        };

        drawer.addDrawerListener(toggle);
        navigationView.setNavigationItemSelectedListener(this);

        ConnectivityManager connMgr = (ConnectivityManager) this.getSystemService(CONNECTIVITY_SERVICE);
        NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
        View navHeader = navigationView.getHeaderView(0);
        if (networkInfo != null && networkInfo.isConnected()) {
            TextView connectionStatus = (TextView) navHeader.findViewById(R.id.connection_status);
            connectionStatus.setText(R.string.common_online);
        } else {
            TextView connectionStatus = (TextView) navHeader.findViewById(R.id.connection_status);
            connectionStatus.setText(R.string.common_offline);
        }

        toggle.syncState();

        GwApiAccess gwApiAccess = new GwApiAccess(this,"https://api.guildwars2.com/v2/items/30704?lang=de");
    }

    @Override
    protected void onPostCreate(Bundle savedInstanceState) {
        super.onPostCreate(savedInstanceState);
        // Sync the toggle state after onRestoreInstanceState has occurred.
        toggle.syncState();
    }

    @Override
    public void onConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);
        toggle.onConfigurationChanged(newConfig);
    }


    @Override
    public void onBackPressed() {
        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 onPrepareOptionsMenu(Menu menu) {
        // If the nav drawer is open, hide action items related to the content view
        boolean drawerOpen = drawer.isDrawerOpen(GravityCompat.START);
        return super.onPrepareOptionsMenu(menu);
    }


    @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();

        if (id == R.id.nav_profile) {
            Intent intent = new Intent(this,profile.class);
            startActivity(intent);
        } else if (id == R.id.nav_itemDB) {
            Intent intent = new Intent(this,items.class);
            startActivity(intent);
        } else if (id == R.id.nav_guilds) {
            Intent intent = new Intent(this,guilds.class);
            startActivity(intent);
        } else if (id == R.id.nav_maps) {
            Intent intent = new Intent(this,map.class);
            startActivity (intent);
        } else if (id == R.id.settings) {
            Intent intent = new Intent(this,SettingsActivity.class);
            startActivity (intent);
        }

        drawer.closeDrawer(GravityCompat.START);
        return true;
    }
}

Harshad Pansuriya · Accepted Answer · 2016-06-19T05:41:33.317

First change this part

 @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        toolbar = (Toolbar) findViewById(R.id.toolbar);
        drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        navigationView = (NavigationView) findViewById(R.id.nav_view);
        setSupportActionBar(toolbar);
        setContentView(R.layout.activity_main);

to this

 @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);       
        setContentView(R.layout.activity_main);
        toolbar = (Toolbar) findViewById(R.id.toolbar);
        drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        navigationView = (NavigationView) findViewById(R.id.nav_view);
        setSupportActionBar(toolbar);

Because you are not set layout to Actiivty before that you have to access it inner element so that the Studio can't find it and it give you NullpointerExeception.

Ok, thx worked! But what was my fault, I'd like to understand my failure for future apps! — school_guy, Jun 19 '16 at 05:38
@school_guy you can accept the answer if this answer helpful to you. — Harshad Pansuriya, Jun 19 '16 at 05:39
You answered to fast Stackoverflow prevented me from checking — school_guy, Jun 19 '16 at 05:42

NPE at adding Drawer Listener

1 Answers1