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I am trying to make a three tab layout, but my code keeps returning a NullPointerException!
I made another project just for that (following this tutorial: https://examples.javacodegeeks.com/android/core/widget/android-tablayout-example/ ), and everything worked perfectly. But when I made the same changes to my original project, "TabLayout" kept receiving "null", causing the application to crash when I request that specific activity. I tried debugging, but as I'm new to all of this, I couldn't figure anything out of it.

Here is the code from the activity that's gonna "host" the tabs and stuff:

public class Dashboard extends AppCompatActivity {

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);



        //Here is where the code gets the Null value:

        TabLayout tabLayout = ( TabLayout) findViewById(R.id.tab_layout);



        //Here is where the app crashes (on "First Tab", because of the same Null value):

        tabLayout.addTab(tabLayout.newTab().setText("First Tab"));

        tabLayout.addTab(tabLayout.newTab().setText("Second Tab"));

        tabLayout.addTab(tabLayout.newTab().setText("Third Tab"));

        tabLayout.setTabGravity(TabLayout.GRAVITY_FILL);



        final ViewPager viewPager = (ViewPager) findViewById(R.id.pager);

        final PagerAdapter adapter = new PagerAdapter

                (getSupportFragmentManager(), tabLayout.getTabCount());

        viewPager.setAdapter(adapter);

        viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));

        tabLayout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {



            @Override

            public void onTabSelected(TabLayout.Tab tab) {

                viewPager.setCurrentItem(tab.getPosition());

            }



            @Override

            public void onTabUnselected(TabLayout.Tab tab) {

            }



            @Override

            public void onTabReselected(TabLayout.Tab tab) {

            }

        });

    }

}

This is the message I get:

Process: festei.fun.festeisocialandroid, PID: 7285

    java.lang.RuntimeException: Unable to start activity ComponentInfo{festei.fun.festeisocialandroid/festei.fun.festeisocialandroid.Dashboard}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.support.design.widget.TabLayout$Tab android.support.design.widget.TabLayout.newTab()' on a null object reference

        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2830)

        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2909)

        at android.app.ActivityThread.-wrap11(Unknown Source:0)

        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1606)

        at android.os.Handler.dispatchMessage(Handler.java:105)

        at android.os.Looper.loop(Looper.java:164)

        at android.app.ActivityThread.main(ActivityThread.java:6592)

        at java.lang.reflect.Method.invoke(Native Method)

        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)

        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:769)

     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.support.design.widget.TabLayout$Tab android.support.design.widget.TabLayout.newTab()' on a null object reference

        at festei.fun.festeisocialandroid.Dashboard.onCreate(Dashboard.java:19)

        at android.app.Activity.performCreate(Activity.java:6984)

        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1235)

        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2783)

        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2909) 

        at android.app.ActivityThread.-wrap11(Unknown Source:0) 

        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1606) 

        at android.os.Handler.dispatchMessage(Handler.java:105) 

        at android.os.Looper.loop(Looper.java:164) 

        at android.app.ActivityThread.main(ActivityThread.java:6592) 

        at java.lang.reflect.Method.invoke(Native Method) 

        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240) 

        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:769)