Почему findViewById возвращает ноль? ⇐ JAVA

[Anonymous]

Почему мой findViewById возвращает здесь значение null swipeRefreshLayout = findViewById(R.id.swipeRefreshLayoutDashboard);?
Я уже пробовал использовать .getRootView() и спускаюсь по иерархии самостоятельно, но безуспешно. Можете ли вы мне помочь?
DashboardActivity.java
package eu.app;

import android.app.AlertDialog;
import android.app.DialogFragment;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.NavigationView;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v4.widget.SwipeRefreshLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import com.github.mikephil.charting.charts.LineChart;
import com.github.mikephil.charting.components.YAxis;
import com.github.mikephil.charting.data.Entry;
import com.github.mikephil.charting.data.LineData;
import com.github.mikephil.charting.data.LineDataSet;
import com.github.mikephil.charting.utils.EntryXComparator;

import java.util.ArrayList;
import java.util.Calendar;
import java.util.Collections;
import java.util.List;
public class DashboardActivity extends AppCompatActivity
implements NavigationView.OnNavigationItemSelectedListener {

private SwipeRefreshLayout swipeRefreshLayout;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_dashboard);
Toolbar toolbar = findViewById(R.id.toolbar);
setSupportActionBar(toolbar);

FloatingActionButton fab = findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
DialogFragment fragment = new AddWeightDialog();
fragment.show(getFragmentManager(), "fab");
}
});

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

swipeRefreshLayout = findViewById(R.id.swipeRefreshLayoutDashboard);
swipeRefreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
@Override
public void onRefresh() {
Log.i("onRefreshListener", "refreshing");
update();
}
});
}
}

activity_dashboard.xml:









app_bar_dashboard.xml















content_dashboard.xml


















Подробнее здесь: https://stackoverflow.com/questions/499 ... eturn-null