Why after clicking + icon in the appbar the app crashes? Showing null pointer exception

Question

I am not getting the up button(in fact activity_order activity doesn't start).It crashes when i click the icon (+) in MainActivity appbar

I have this intuition that there is something wrong with

getSupportActionBar().setDisplayHomeAsUpEnabled(true);

This is the second activity

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.Toolbar;
public class activity_order extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_order);
        Toolbar toolbar=(Toolbar) findViewById(R.id.toolbar_main);
        setSupportActionBar(toolbar);
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    }

}

This is the main/parent activity

import android.content.Intent;
import android.support.v4.view.MenuItemCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.ShareActionProvider;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
public class MainActivity extends AppCompatActivity {

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

    @Override
    public boolean onCreateOptionsMenu(Menu menu)
    {
        getMenuInflater().inflate(R.menu.menu_main,menu);
        return super.onCreateOptionsMenu(menu);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item)
    {
            if(R.id.action_create_order==item.getItemId()) {
                Intent intent = new Intent(this, activity_order.class);
                startActivity(intent);
                return true;
            }
        return super.onOptionsItemSelected(item);

    }

 }

Error Log


2019-06-18 22:51:49.374 4127-4147/com.example.orderpizza I/Adreno: QUALCOMM build                   : f47ef91, I09d312ff84
    Build Date                       : 07/24/17
    OpenGL ES Shader Compiler Version: XE031.09.00.04
    Local Branch                     : 
    Remote Branch                    : refs/tags/AU_LINUX_ANDROID_LA.UM.5.5.R1.07.01.02.269.046
    Remote Branch                    : NONE
    Reconstruct Branch               : NOTHING
2019-06-18 22:51:49.383 4127-4147/com.example.orderpizza I/OpenGLRenderer: Initialized EGL, version 1.4
2019-06-18 22:51:49.383 4127-4147/com.example.orderpizza D/OpenGLRenderer: Swap behavior 1
2019-06-18 22:51:49.418 4127-4127/com.example.orderpizza W/art: Before Android 4.1, method int android.support.v7.widget.DropDownListView.lookForSelectablePosition(int, boolean) would have incorrectly overridden the package-private method in android.widget.ListView
2019-06-18 22:51:52.150 4127-4127/com.example.orderpizza V/BoostFramework: BoostFramework() : mPerf = com.qualcomm.qti.Performance@7d39c7c
2019-06-18 22:51:52.269 4127-4127/com.example.orderpizza I/Timeline: Timeline: Activity_launch_request time:28140110 intent:Intent { cmp=com.example.orderpizza/.activity_order }
2019-06-18 22:51:52.317 4127-4127/com.example.orderpizza D/AndroidRuntime: Shutting down VM
2019-06-18 22:51:52.318 4127-4127/com.example.orderpizza E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.orderpizza, PID: 4127
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.orderpizza/com.example.orderpizza.activity_order}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2757)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2818)
        at android.app.ActivityThread.-wrap12(ActivityThread.java)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1557)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:163)
        at android.app.ActivityThread.main(ActivityThread.java:6393)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:933)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:823)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
        at com.example.orderpizza.activity_order.onCreate(activity_order.java:16)
        at android.app.Activity.performCreate(Activity.java:6858)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2710)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2818) 
        at android.app.ActivityThread.-wrap12(ActivityThread.java) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1557) 
        at android.os.Handler.dispatchMessage(Handler.java:102) 
        at android.os.Looper.loop(Looper.java:163) 
        at android.app.ActivityThread.main(ActivityThread.java:6393) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:933) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:823) 
2019-06-18 22:51:52.337 4127-4127/com.example.orderpizza I/Process: Sending signal. PID: 4127 SIG: 9

Please help as I am not getting why is it showing a nullPointerException.

Possible duplicate of [What is a NullPointerException, and how do I fix it?](https://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do-i-fix-it) — Zoe, Jun 18 '19 at 18:28
Sorry ,but you are mistaken....This is problem regarding android and method ```actionBar.setDisplayHomeUpEnabled(true);```throwning null pointer exception....As in the android docs it is suppose not to throw nullpointerexception....Thanks for your concern — Vikas Kumar, Jun 19 '19 at 11:46

score 0 · Answer 1 · answered Jun 18 '19 at 17:49

0

You probably is not using the support library, if you're importing android.app.ActionBar you should user getActionBar() instead. Or just import android.support.v7.app.ActionBar.
To your safety, always check if getSupportActionBar() != null as well

answered Jun 18 '19 at 17:49

Shermano

1,100
8
31

Mohimenul Joaa · Answer 2 · 2019-06-18T18:33:30.860

i think your activity_order layout don't have any Toolbar xml with id toolbar_main please recheck that... you should at least have a appbarlayout and a toolbar

<android.support.design.widget.AppBarLayout
        android:id="@+id/my_appbarLayout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:elevation="0dp"
        android:theme="@style/AppTheme.AppBarOverlay"
        app:elevation="0dp">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar_main"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:layout_margin="0dp"
            app:layout_scrollFlags="snap"
            app:navigationIcon="@drawable/ic_arrow_back_black_24dp"
            app:popupTheme="@style/AppTheme.PopupOverlay"
            app:theme="@style/ThemeToolbar.default" />

    </android.support.design.widget.AppBarLayout>

Why after clicking + icon in the appbar the app crashes? Showing null pointer exception

2 Answers2