My app crashes on launch with getActionBar()

Question

I am making an app with view pager and fragments. But it crashes on launch so can you please help me finding the error in my code. I am providing both my code and Logcat. I am learning the tutorial from this website : https://www.androidhive.info/2013/10/android-tab-layout-with-swipeable-views-1/

package com.example.android.resume;

 import android.app.ActionBar;
 import android.app.ActionBar.Tab;
 import android.app.FragmentTransaction;
 import android.os.Bundle;
 import android.support.v4.app.FragmentActivity;
 import android.support.v4.view.ViewPager;

 import tabsswiper.TabsPagerAdapter;

 public class MainActivity extends FragmentActivity implements 
 ActionBar.TabListener {

private ViewPager viewPager;
private TabsPagerAdapter mAdapter;
private ActionBar actionBar;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    String[] tabs = {"About Me", "Sample Photos", "Book Me"};

    // Initilization
    viewPager = findViewById(R.id.pager);
    actionBar = getActionBar();
    mAdapter = new TabsPagerAdapter(getSupportFragmentManager());

    viewPager.setAdapter(mAdapter);
    actionBar.setHomeButtonEnabled(false);
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

    // Adding Tabs
    for (String tab_name : tabs) {
        actionBar.addTab(actionBar.newTab().setText(tab_name)
                .setTabListener(this));
    }

    /*
     * on swiping the viewpager make respective tab selected
     * */
    viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {

        @Override
        public void onPageSelected(int position) {
            // on changing the page
            // make respected tab selected
            actionBar.setSelectedNavigationItem(position);
        }

        @Override
        public void onPageScrolled(int arg0, float arg1, int arg2) {
        }

        @Override
        public void onPageScrollStateChanged(int arg0) {
        }
    });
}

@Override
public void onTabReselected(Tab tab, FragmentTransaction ft) {
}

@Override
public void onTabSelected(Tab tab, FragmentTransaction ft) {
    // on tab selected
    // show respected fragment view
    viewPager.setCurrentItem(tab.getPosition());
}

@Override
public void onTabUnselected(Tab tab, FragmentTransaction ft) {
   }
}

My Logcat :

 FATAL EXCEPTION: main
                                                                        Process: com.example.android.resume, PID: 32723
                                                                        java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.android.resume/com.example.android.resume.MainActivity}: java.lang.NullPointerException
                                                                            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2381)
                                                                            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2433)
                                                                            at android.app.ActivityThread.access$800(ActivityThread.java:155)
                                                                            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1346)
                                                                            at android.os.Handler.dispatchMessage(Handler.java:110)
                                                                            at android.os.Looper.loop(Looper.java:193)
                                                                            at android.app.ActivityThread.main(ActivityThread.java:5341)
                                                                            at java.lang.reflect.Method.invokeNative(Native Method)
                                                                            at java.lang.reflect.Method.invoke(Method.java:515)
                                                                            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:830)
                                                                            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:646)
                                                                            at dalvik.system.NativeStart.main(Native Method)
                                                                         Caused by: java.lang.NullPointerException
                                                                            at com.example.android.resume.MainActivity.onCreate(MainActivity.java:30)
                                                                            at android.app.Activity.performCreate(Activity.java:5343)
                                                                            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1088)
                                                                            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2335)
                                                                            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2433) 
                                                                            at android.app.ActivityThread.access$800(ActivityThread.java:155) 
                                                                            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1346) 
                                                                            at android.os.Handler.dispatchMessage(Handler.java:110) 
                                                                            at android.os.Looper.loop(Looper.java:193) 
                                                                            at android.app.ActivityThread.main(ActivityThread.java:5341) 
                                                                            at java.lang.reflect.Method.invokeNative(Native Method) 
                                                                            at java.lang.reflect.Method.invoke(Method.java:515) 
                                                                            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:830) 
                                                                            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:646) 
                                                                            at dalvik.system.NativeStart.main(Native Method)

check this https://www.androidhive.info/2015/09/android-material-design-working-with-tabs/ — Goku, Nov 22 '17 at 11:30
check your activity theme it will be with no action bar so if you want action bar than use the theme with action bar — pankaj yadav, Nov 22 '17 at 11:51

score 3 · Answer 1 · answered Nov 22 '17 at 11:44

3

Use AppCompactActivity in place of FragmentActivity and also use Toolbar as

 toolbar = (Toolbar) findViewById(R.id.toolbar);
 setSupportActionBar(toolbar);
 getSupportActionBar().setDisplayHomeAsUpEnabled(true);

answered Nov 22 '17 at 11:44

Akshay Barodia

486
4
11

score 0 · Answer 2 · answered Nov 22 '17 at 11:31

0

you can use getSupportActionBar() instead of getActionBar() method.

answered Nov 22 '17 at 11:31

Sanket

413
2
15

but it says cannot resolve symbol getSupportActionBar( – Sanchit Jain Nov 22 '17 at 11:34
you need to change Change "public class MainActivity extends FragmentActivity" as "public class MainActivity extends AppCompatActivity" and also add "compile "com.android.support:appcompat-v7:+" in Gradle file – Sanket Nov 23 '17 at 09:08

score 0 · Answer 3 · answered Nov 22 '17 at 11:44

You should use getSupportActionBar() instead of getActionBar().

Firstly remove your import of

import android.app.ActionBar;

and then check if you declared the supported of v7 in dependence as below

compile 'com.android.support:appcompat-v7:+'

good luck.

score 0 · Answer 4 · answered Nov 22 '17 at 11:48

0

Try

getContext().getActionBar()

or

getContext().getSupportActionBar()

answered Nov 22 '17 at 11:48

Muhammad Saad Rafique

3,158
1
13
21

score 0 · Answer 5 · answered Nov 22 '17 at 12:11

Try this one

package com.demotest;
import android.os.Bundle;
import android.support.v4.app.FragmentTransaction;
import android.support.v4.view.ViewPager;
import android.support.v7.app.ActionBar;
import android.support.v7.app.AppCompatActivity;

public class MainActivity  extends AppCompatActivity implements
    ActionBar.TabListener {

private ViewPager viewPager;
private TabsPagerAdapter mAdapter;
private ActionBar actionBar;
// Tab titles
private String[] tabs = {"Top Rated", "Games", "Movies"};

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

    // Initilization
    viewPager = (ViewPager) findViewById(R.id.pager);
    actionBar = getSupportActionBar();
    mAdapter = new TabsPagerAdapter(getSupportFragmentManager());

    viewPager.setAdapter(mAdapter);
    actionBar.setHomeButtonEnabled(false);
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

    // Adding Tabs
    for (String tab_name : tabs) {
        actionBar.addTab(actionBar.newTab().setText(tab_name)
                .setTabListener(MainActivity.this));
    }

    viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
        @Override
        public void onPageScrolled(int position, float positionOffset, int 
    positionOffsetPixels) {
            actionBar.setSelectedNavigationItem(position);

        }

        @Override
        public void onPageSelected(int position) {

        }

        @Override
        public void onPageScrollStateChanged(int state) {

        }
    });
}




@Override
public void onTabSelected(ActionBar.Tab tab, FragmentTransaction ft) {
    viewPager.setCurrentItem(tab.getPosition());
}

@Override
public void onTabUnselected(ActionBar.Tab tab, FragmentTransaction ft) {

}

@Override
public void onTabReselected(ActionBar.Tab tab, FragmentTransaction ft) {

}


}

My app crashes on launch with getActionBar()

5 Answers5