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How can I access a TextView in the onCreate function?

Hi have been using fragments and have a drawer header which is going to display the currently logged in user.
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.drawerlayout.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/drawer"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_centerHorizontal="false"
android:background="?android:attr/colorBackground"
tools:context=".MainActivity">
<include
layout="#layout/drawer_toolbar"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
<include
layout="#layout/content_main"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
<com.google.android.material.navigation.NavigationView
android:id="#+id/navigationView"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_gravity="start"
android:fitsSystemWindows="true"
app:headerLayout="#layout/drawer_header"
app:menu="#menu/drawer_menu" />
</androidx.drawerlayout.widget.DrawerLayout>
This is the code that creates the layout and the adds the header and menu to the navigation view. I am trying to access the text stored in the drawer header with an id.
The problem i get is that when it tries to set the variable usernameHeader to the id "user" it throws an error saying that there is a null object reference. My understanding is that the drawer is create during the onCreate when it says "actionBarDrawerToggle = new ActionBarDrawerToggle(this, drawerLayout, toolbar, R.string.open, R.string.close);" i could be wrong and any help is greatly appreciated. Thanks in advance
UPDATE:
I have rewritten and minimal example to show the exact part where it breaks.
I have added the drawer_header.xml which contains the TextView with the id 'user'. I have also added the minimal version of the MainActivity.
drawer_header.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="150dp"
android:background="#color/teal_700">
<TextView
android:id="#+id/user"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="25dp"
android:text="#string/user"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
MainActivity.java
package com.secureit.drawerfragment;
import android.os.Bundle;
import android.view.MenuItem;
import android.widget.TextView;
import androidx.annotation.NonNull;
import androidx.appcompat.app.ActionBarDrawerToggle;
import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;
import androidx.core.view.GravityCompat;
import androidx.drawerlayout.widget.DrawerLayout;
import com.google.android.material.navigation.NavigationView;
public class MainActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener {
DrawerLayout drawerLayout;
ActionBarDrawerToggle actionBarDrawerToggle;
Toolbar toolbar;
NavigationView navigationView;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
toolbar = findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
drawerLayout = findViewById(R.id.drawer);
navigationView = findViewById(R.id.navigationView);
navigationView.setNavigationItemSelectedListener(this);
actionBarDrawerToggle = new ActionBarDrawerToggle(this, drawerLayout, toolbar, R.string.open, R.string.close);
drawerLayout.addDrawerListener(actionBarDrawerToggle);
actionBarDrawerToggle.setDrawerIndicatorEnabled(true);
actionBarDrawerToggle.syncState();
TextView textView = findViewById(R.id.user); // This is where the error shows "Null object reference"
textView.setText("user");
}
#Override
public boolean onNavigationItemSelected(#NonNull MenuItem item) {
drawerLayout.closeDrawer(GravityCompat.START);
return false;
}
}

The problem is, you are accessing a TextView in different view from your activity. You should inflate your header view first and then use that to access your TextView. Add this to your onCreate method.
View headerView = navigationView.getHeaderView(0);
TextView txtUser= headerView.findViewById(R.id.user);
txtUser.setText("user");

How can I add drawerLayout and not to damage existed LinerLayout style?

I began doing a project without DrawableLayout. I am using mostly LinearLayout. I want to add drawer navigation android, and as I know, I need DrawableLayout.
How can I add this, and not damage everything I have now?

Well don't be afraid. It's not so difficult. Just follow the following steps to get it:-
<android.support.v4.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="#+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#android:color/holo_green_dark">
<!-- put you linear layout here --!>
<android.support.design.widget.NavigationView
android:layout_width="wrap_content"
android:layout_height="match_parent"
app:menu="#menu/navigation_menu"
android:layout_gravity="start"
app:headerLayout="#layout/nav_header"
android:id="#+id/nv">
</android.support.design.widget.NavigationView>
</android.support.v4.widget.DrawerLayout>
Navigation Header:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center"
android:background="#color/colorPrimaryDark">
<ImageView
android:layout_width="180dp"
android:layout_height="130dp"
android:layout_marginBottom="15dp"
android:layout_marginTop="15dp"
android:background="#drawable/ic_android_black_24dp"/>
</LinearLayout>
**Create a menu for the navigation drawer**
Right-click the res folder →Select new →Android resource file →Choose ‘menu’ under the resource type drop-down list.
Name the file as ‘navigation_menu.xml’ and copy-paste the following code into the file.
`<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
<item android:id="#+id/account"
android:icon="#drawable/ic_portrait_black_24dp"
android:title="My Account"/>
<item android:id="#+id/settings"
android:icon="#drawable/ic_brightness_high_black_24dp"
android:title="Settings"/>
<item android:id="#+id/mycart"
android:icon="#drawable/ic_local_grocery_store_black_24dp"
android:title="My Cart"/>
</menu>
** Lastly, in you activity:** <br>
In this last and final step, we will write Java code in the MainActivity.java file.
import android.support.annotation.NonNull;
import android.support.design.widget.NavigationView;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.MenuItem;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
private DrawerLayout dl;
private ActionBarDrawerToggle t;
private NavigationView nv;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
dl = (DrawerLayout)findViewById(R.id.activity_main);
t = new ActionBarDrawerToggle(this, dl,R.string.Open, R.string.Close);
dl.addDrawerListener(t);
t.syncState();
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
nv = (NavigationView)findViewById(R.id.nv);
nv.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
#Override
public boolean onNavigationItemSelected(#NonNull MenuItem item) {
int id = item.getItemId();
switch(id)
{
case R.id.account:
Toast.makeText(MainActivity.this, "My Account",Toast.LENGTH_SHORT).show();break;
case R.id.settings:
Toast.makeText(MainActivity.this, "Settings",Toast.LENGTH_SHORT).show();break;
case R.id.mycart:
Toast.makeText(MainActivity.this, "My Cart",Toast.LENGTH_SHORT).show();break;
default:
return true;
}
return true;
}
});
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
if(t.onOptionsItemSelected(item))
return true;
return super.onOptionsItemSelected(item);
}
}`

DrawerToggle Hamburger icon not showing

I am new to android. currently, I am making an android app with a navigation drawer. I managed to add the drawer. and when slid it works properly. but my problem is I cannot manage to add a hamburger icon.
my minimum sdk version is 17
I tried every solution given in the previous problems but didn't work.
My main activity code
package com.example.myapplication;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import androidx.appcompat.app.ActionBarDrawerToggle;
import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;
import androidx.drawerlayout.widget.DrawerLayout;
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar myToolbar = (Toolbar) findViewById(R.id.my_toolbar);
setSupportActionBar(myToolbar);
getSupportActionBar().setDisplayShowTitleEnabled(false);
getSupportActionBar().setHomeButtonEnabled(true);
getSupportActionBar().setDefaultDisplayHomeAsUpEnabled(true);
DrawerLayout drawer =(DrawerLayout) findViewById(R.id.drawer_layout);
ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(this, drawer, R.string.open, R.string.close);
drawer.addDrawerListener(toggle);
toggle.setDrawerIndicatorEnabled(true);
toggle.syncState();
}
// Menu icons are inflated just as they were with actionbar
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
}
my xml code
<?xml version="1.0" encoding="utf-8"?>
<androidx.drawerlayout.widget.DrawerLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:openDrawer="left">
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#E0E0E0"
tools:context=".MainActivity"
android:fitsSystemWindows="true">
<androidx.appcompat.widget.Toolbar
android:id="#+id/my_toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="#null"
android:theme="#style/ThemeOverlay.AppCompat.ActionBar"
app:popupTheme="#style/ThemeOverlay.AppCompat.Light" />
</RelativeLayout>
<com.google.android.material.navigation.NavigationView
android:id="#+id/nav_view"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_gravity="start"
app:menu="#menu/activity_main_drawer"
android:fitsSystemWindows="true"/>
</androidx.drawerlayout.widget.DrawerLayout>

Everything looks fine, You just need to pass the toolbar object into the ActionBarDrawerToggle constructer as a third argument.
ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(this, drawer, myToolbar, R.string.open, R.string.close);
here

Check out the following example:
MainActivity.class
public class MainActivity extends AppCompatActivity {
private final String TAG = MainActivity.class.getSimpleName();
private ActionBarDrawerToggle toggle = null;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar myToolbar = (Toolbar) findViewById(R.id.my_toolbar);
setSupportActionBar(myToolbar);
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
final ActionBar actionBar = getSupportActionBar();
if (actionBar != null) {
actionBar.setDisplayShowTitleEnabled(false);
actionBar.setHomeButtonEnabled(true);
actionBar.setDefaultDisplayHomeAsUpEnabled(true);
toggle = new ActionBarDrawerToggle(this, drawer, myToolbar, R.string.open, R.string.close) {
public void onDrawerClosed(View view) {
supportInvalidateOptionsMenu();
}
public void onDrawerOpened(View drawerView) {
supportInvalidateOptionsMenu();
}
};
toggle.setDrawerIndicatorEnabled(true);
drawer.addDrawerListener(toggle);
toggle.syncState();
}
}
#Override
protected void onPostCreate(Bundle savedInstanceState) {
super.onPostCreate(savedInstanceState);
if(toggle != null) {
toggle.syncState();
}
}
#Override
public void onConfigurationChanged(Configuration newConfig) {
super.onConfigurationChanged(newConfig);
if (toggle != null) {
toggle.onConfigurationChanged(newConfig);
}
}
}
activity_main.xml:
<?xml version="1.0" encoding="utf-8"?>
<androidx.drawerlayout.widget.DrawerLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:context=".MainActivity">
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#E0E0E0"
android:fitsSystemWindows="true">
<androidx.appcompat.widget.Toolbar
android:id="#+id/my_toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="#null"
android:theme="#style/ThemeOverlay.AppCompat.ActionBar"
app:popupTheme="#style/ThemeOverlay.AppCompat.Light" />
</RelativeLayout>
<TextView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:text="Text View"
android:textSize="35sp"
android:background="#color/colorAccent"
android:layout_gravity="start"
android:gravity="center">
</TextView>
</androidx.drawerlayout.widget.DrawerLayout>

How to use own layout for navigation drawer activity instead of auto generated layout?

I have a navigation drawer activity, that have automatically generated these activity_student_home2, app_bar_student_home, content_student_home, nav_header_student_home layout files. I have separately created activity_student_home layout.By default the activity java class has the acitivity_student_home2 layout as setContentView. But instead, I want to use the acitivity_student_home layout. If I try to change the setContentView to acitivity_student_home then my navigation drawer view does not work. How can I use the acitivity_student_home layout as setContentView?
activity_student_home layout:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#drawable/app_back"
tools:context="bd.edu.bubt.regup.StudentHomeActivity">
<LinearLayout
android:layout_centerHorizontal="true"
android:layout_centerVertical="false"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginLeft="60dp"
android:id="#+id/linearLayout">
<TextView
android:id="#+id/showtext"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="300dp"
android:gravity="center"
android:text="Demo"
android:textSize="24dp"
android:textStyle="bold" />
</LinearLayout>
</RelativeLayout>
activity_student_home2 layout:
<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:openDrawer="start">
<include
layout="#layout/app_bar_student_home"
android:layout_width="match_parent"
android:layout_height="match_parent" />
<android.support.design.widget.NavigationView
android:id="#+id/nav_view"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_gravity="start"
android:fitsSystemWindows="true"
app:headerLayout="#layout/nav_header_student_home"
app:menu="#menu/activity_student_home2_drawer" />
</android.support.v4.widget.DrawerLayout>
app_bar_student_home layout:
<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#drawable/app_back"
tools:context="bd.edu.bubt.regup.StudentHomeActivity">
<android.support.design.widget.AppBarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="#style/AppTheme.AppBarOverlay">
<android.support.v7.widget.Toolbar
android:id="#+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="?attr/colorPrimary"
app:popupTheme="#style/AppTheme.PopupOverlay" />
</android.support.design.widget.AppBarLayout>
<include layout="#layout/content_student_home" />
</android.support.design.widget.CoordinatorLayout>
StudentHomeActivity java class:
import android.app.ProgressDialog;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
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;
public class StudentHomeActivity extends AppCompatActivity
implements NavigationView.OnNavigationItemSelectedListener {
String name, id, dept, intake, sec, mail;
TextView showtext;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_student_home2);
showtext = (TextView) findViewById(R.id.showtext); //content of activity_student_home
showtext.setText("Registration is open"); //does not work. Null pointer exception.
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
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);
}
#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 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.menu_bvault) {
// Handle the camera action
} else if (id == R.id.menu_account) {
} else if (id == R.id.menu_pass_change) {
} else if (id == R.id.menu_logout) {
} else if (id == R.id.menu_about) {
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
}
}

Your activity_student_home does not include your DrawerLayout
This is missing
<include
layout="#layout/app_bar_student_home"
android:layout_width="match_parent"
android:layout_height="match_parent" />

The correct way to do what you wish is (if I understand what you are asking for correctly) to use fragments
Inside your app_bar_student_home.xml replace
<include layout="#layout/content_student_home" />
with something like this
<FrameLayout
android:id="#+id/content"
android:layout_width="match_parent"
app:layout_behavior="#string/appbar_scrolling_view_behavior"
android:layout_height="match_parent"/>
Then create fragments whose content you wish to show (let's say FragmentA, FragmentB) and set their contentview to the different layouts you wish to show
when you wish to change the content for your activity you can do something like
getSupportFragmentManager().beginTransaction().replace(R.id.content, new FragmentA()).commit();
there's a lot more to it than this,
for example when you wish to send a click event from the fragment to your activity you have to use getActivity() and cast it to the class of your MainActivity or use an interface (preferable)
you can check out this tutorial which should help you
http://www.androiddocs.com/training/basics/fragments/index.html

Android App Crash On Button Click

I am building an app and on a button click the app crashes. The app was working perfectly about a week ago and the code has not been altered in anyway since the last time I tested it. Now when I click the Login in button it crashes. This makes no sense as it hasn't been edited. Source code below.
Login.java
package com.example.martin.ivebeenthere;
import android.content.Intent;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
public class Login extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
}
public void onClickbtnFeed(View view)
{
startActivity(new Intent(Login.this, Feed.class));
}
}
content_login.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
app:layout_behavior="#string/appbar_scrolling_view_behavior"
tools:context="com.example.martin.ivebeenthere.Login"
tools:showIn="#layout/activity_login">
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="#+id/imageView"
android:src="#drawable/logo"
android:layout_alignParentBottom="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_marginBottom="276dp" />
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:inputType="textPersonName"
android:ems="10"
android:hint="Username"
android:id="#+id/editText"
android:layout_centerVertical="true"
android:layout_centerHorizontal="true" />
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:inputType="textPassword"
android:ems="10"
android:hint="Password"
android:id="#+id/editText2"
android:layout_below="#+id/editText"
android:layout_centerHorizontal="true" />
<Button
android:layout_width="200dp"
android:layout_height="wrap_content"
android:text="Login"
android:id="#+id/button3"
android:layout_below="#+id/editText2"
android:layout_centerHorizontal="true"
android:onClick="onClickbtnFeed"/>
<Button
android:layout_width="200dp"
android:layout_height="wrap_content"
android:text="Login With Facebook"
android:id="#+id/button4"
android:background="#3b5998"
android:textColor="#ffffff"
android:layout_below="#+id/button3"
android:layout_alignLeft="#+id/button3"
android:layout_alignStart="#+id/button3"
android:layout_marginTop="25dp" />
</RelativeLayout>
Feed.java (Page Linked With Button)
package com.example.martin.ivebeenthere;
import android.content.Intent;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
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.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;
public class Feed extends AppCompatActivity
implements NavigationView.OnNavigationItemSelectedListener {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_feed);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
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);
String[] users = {"\nMartin Hoban\n\nVisited Dublin 2 Hours Ago\n","\nJack White\n\nVisited Mayo 10 Hours Ago\n","\nSarah Cox\n\nVisited Cork 1 Day Ago\n","\nMalcolm Holmes\n\nVisited Knock 2 Days Ago\n", "\nCraig Fisher\n\nVisited The Spire 2 Days Ago\n", "\nHannah Smith\n\nVisited Mayo 3 Days Ago\n"
,"\nLanelle Delaune\n\nVisited Limerick 1 Week Ago\n", "\nHanna Whitlow\n\nVisited Paris 1 Week Ago\n", "\nMoses Primm\n\nVisited Italy 3 Weeks Ago\n", "\nBerta Pedraza\n\nVisited The Aillwee Caves 1 Month Ago\n"};
ArrayAdapter<String> itemsAdapter =
new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, users);
ListView listView = (ListView) findViewById(R.id.listView);
listView.setAdapter(itemsAdapter);
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
if (position == 4) {
Intent myIntent = new Intent(view.getContext(), CheckinInfo.class);
startActivityForResult(myIntent, 0);
}
}
});
}
#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.feed, menu);
return true;
}
#SuppressWarnings("StatementWithEmptyBody")
#Override
public boolean onNavigationItemSelected(MenuItem item) {
// Handle navigation view item clicks here.
int id = item.getItemId();
if (id == R.id.nav_feed) {
startActivity(new Intent(getApplicationContext(), Feed.class));
} else if (id == R.id.nav_map) {
startActivity(new Intent(getApplicationContext(), Map.class));
} else if (id == R.id.nav_account) {
startActivity(new Intent(getApplicationContext(), Account.class));
} else if (id == R.id.nav_logout) {
startActivity(new Intent(getApplicationContext(), Home.class));
Toast.makeText(getApplicationContext(), "Logged Out",
Toast.LENGTH_LONG).show();
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
}
}
Logcat
Caused by: java.lang.NullPointerException
at com.example.martin.ivebeenthere.Feed.onCreate(Feed.java:38)
at android.app.Activity.performCreate(Activity.java:5047)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2056)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2117) 
at android.app.ActivityThread.access$700(ActivityThread.java:134) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1218) 
at android.os.Handler.dispatchMessage(Handler.java:99) 
at android.os.Looper.loop(Looper.java:137) 
at android.app.ActivityThread.main(ActivityThread.java:4867) 
at java.lang.reflect.Method.invokeNative(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:511) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1007)at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:774) 
at dalvik.system.NativeStart.main(Native Method)
activity_feed.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:openDrawer="start">
<include
layout="#layout/app_bar_feed"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</android.support.v4.widget.DrawerLayout>
app_bar_feed.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:context="com.example.martin.ivebeenthere.Feed">
<android.support.design.widget.AppBarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="#style/AppTheme.AppBarOverlay">
<android.support.v7.widget.Toolbar
android:id="#+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="?attr/colorPrimary"
app:popupTheme="#style/AppTheme.PopupOverlay" />
</android.support.design.widget.AppBarLayout>
<include layout="#layout/content_feed" />
</android.support.design.widget.CoordinatorLayout>
Rendering Problem In Design View of activity_feed.xml
java.lang.IllegalArgumentException: No drawer view found with gravity LEFT
at android.support.v4.widget.DrawerLayout.openDrawer(DrawerLayout.java:1464)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at com.android.layoutlib.bridge.util.ReflectionUtils.invoke(ReflectionUtils.java:45)
at com.android.layoutlib.bridge.android.support.DrawerLayoutUtil.openDrawer(DrawerLayoutUtil.java:56)
at com.android.layoutlib.bridge.android.support.DrawerLayoutUtil.openDrawer(DrawerLayoutUtil.java:50)
at android.view.BridgeInflater.postInflateProcess(BridgeInflater.java:361)
at com.android.layoutlib.bridge.impl.RenderSessionImpl.postInflateProcess(RenderSessionImpl.java:968)
at com.android.layoutlib.bridge.impl.RenderSessionImpl.postInflateProcess(RenderSessionImpl.java:973)
at com.android.layoutlib.bridge.impl.RenderSessionImpl.inflate(RenderSessionImpl.java:235)
at com.android.layoutlib.bridge.Bridge.createSession(Bridge.java:426)
at com.android.ide.common.rendering.LayoutLibrary.createSession(LayoutLibrary.java:350)
at com.android.tools.idea.rendering.RenderTask$2.compute(RenderTask.java:510)
at com.android.tools.idea.rendering.RenderTask$2.compute(RenderTask.java:498)
at com.intellij.openapi.application.impl.ApplicationImpl.runReadAction(ApplicationImpl.java:888)
at com.android.tools.idea.rendering.RenderTask.createRenderSession(RenderTask.java:498)
at com.android.tools.idea.rendering.RenderTask.access$600(RenderTask.java:72)
at com.android.tools.idea.rendering.RenderTask$3.call(RenderTask.java:610)
at com.android.tools.idea.rendering.RenderTask$3.call(RenderTask.java:607)
at com.android.tools.idea.rendering.RenderService.runRenderAction(RenderService.java:362)
at com.android.tools.idea.rendering.RenderTask.render(RenderTask.java:607)
at com.android.tools.idea.rendering.RenderTask.render(RenderTask.java:629)
at com.intellij.android.designer.designSurface.AndroidDesignerEditorPanel$6.run(AndroidDesignerEditorPanel.java:480)
at com.intellij.util.ui.update.MergingUpdateQueue.execute(MergingUpdateQueue.java:320)
at com.intellij.util.ui.update.MergingUpdateQueue.execute(MergingUpdateQueue.java:310)
at com.intellij.util.ui.update.MergingUpdateQueue$2.run(MergingUpdateQueue.java:254)
at com.intellij.util.ui.update.MergingUpdateQueue.flush(MergingUpdateQueue.java:269)
at com.intellij.util.ui.update.MergingUpdateQueue.flush(MergingUpdateQueue.java:227)
at com.intellij.util.ui.update.MergingUpdateQueue.run(MergingUpdateQueue.java:217)
at com.intellij.util.concurrency.QueueProcessor.runSafely(QueueProcessor.java:238)
at com.intellij.util.Alarm$Request$1.run(Alarm.java:351)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)

I think that the referenced dimension resource can't be found.
The reason may be, you have dimensions specified for specific screen sizes only.
your content.xml:
android:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
define them in values-820dp/dimens.xml or define them in content.xml
you can remove them too.

The local variable navigationView is null. That means there's no view with id nav_view in your activity_feed layout. Make sure to include all views you try to find with findViewById() in onCreate() into the layout.