Versuch zum aufrufen der virtuellen Methode void android.Unterstützung.v7.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' auf ein null-Objekt Verweis

Ich bin mit diesem Fehler. Ich habe verbringen eine Menge Zeit, aber leider!!!! Ich bin stecken in dieser Fehler. Ich möchte hinzufügen Action Bar in meiner app aber es ist kontinuierlich zeigt mir diese Fehlermeldung an getSupportActionBar(), Bitte jemand, der mich anleitet.

FATAL EXCEPTION: main
Process: com.technerdshub.vusocial, PID: 20633
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.technerdshub.vusocial/com.technerdshub.vusocial.Activities.StudentDashboardActivity}: 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:2693)
  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2758)
  at android.app.ActivityThread.access$900(ActivityThread.java:177)
  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1448)
  at android.os.Handler.dispatchMessage(Handler.java:102)
  at android.os.Looper.loop(Looper.java:145)
  at android.app.ActivityThread.main(ActivityThread.java:5942)
  at java.lang.reflect.Method.invoke(Native Method)
  at java.lang.reflect.Method.invoke(Method.java:372)
  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1389)
  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1184)
 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.technerdshub.vusocial.Activities.StudentDashboardActivity.onCreate(StudentDashboardActivity.java:50)
   

Meine java Datei:

package com.technerdshub.vusocial.Activities;

import android.app.Activity;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.support.design.widget.TabLayout;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.widget.Toolbar;
import android.support.v7.app.AppCompatActivity;

import com.google.android.gms.appindexing.Action;
import com.google.android.gms.appindexing.AppIndex;
import com.google.android.gms.common.api.GoogleApiClient;
import com.technerdshub.vusocial.Fragments.TaskFragment;
import com.technerdshub.vusocial.Fragments.dummy.DummyContent;
import com.technerdshub.vusocial.R;

import java.util.ArrayList;
import java.util.List;

public class StudentDashboardActivity extends AppCompatActivity {

    //private Toolbar toolbar;
    private TabLayout tabLayout;
    private ViewPager viewPager;
    /**
     * ATTENTION: This was auto-generated to implement the App Indexing API.
     * See https://g.co/AppIndexing/AndroidStudio for more information.
     */
    private GoogleApiClient client;

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        displayLoginActivity();

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_student_dashboard);

//       Parse.initialize(new Parse.Configuration.Builder(this)
//                       .applicationId("J5CIV2z6xeSCXDqdOfhE0kPSikvRFPyDyOJxqJNx")
//                       .clientKey("bEWm4nWtWiBrMczGfOvA7s4Ulr2bAU3W3TtVSLDf")
//                       .build()
//       );

        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        getSupportActionBar().setElevation(2);


        viewPager = (ViewPager) findViewById(R.id.viewpager);
        setupViewPager(viewPager);

        tabLayout = (TabLayout) findViewById(R.id.tabs);
        tabLayout.setupWithViewPager(viewPager);

//       ParseObject testObject = new ParseObject("Task");
//       testObject.put("marks", 99);
//       testObject.saveInBackground();

        //ATTENTION: This was auto-generated to implement the App Indexing API.
        //See https://g.co/AppIndexing/AndroidStudio for more information.
        client = new GoogleApiClient.Builder(this).addApi(AppIndex.API).build();
    }

    private void setupViewPager(ViewPager viewPager) {
        ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());
        adapter.addFragment(new TaskFragment(), "Quiz");
        adapter.addFragment(new TaskFragment(), "Assignment");
        adapter.addFragment(new TaskFragment(), "GDP");
        viewPager.setAdapter(adapter);
    }



    private void displayLoginActivity() {

        Intent i = new Intent(this, Login.class);
        startActivity(i);

    }

    @Override
    public void onStart() {
        super.onStart();

        //ATTENTION: This was auto-generated to implement the App Indexing API.
        //See https://g.co/AppIndexing/AndroidStudio for more information.
        client.connect();
        Action viewAction = Action.newAction(
                Action.TYPE_VIEW, //TODO: choose an action type.
                "StudentDashboard Page", //TODO: Define a title for the content shown.
                //TODO: If you have web page content that matches this app activity's content,
                //make sure this auto-generated web page URL is correct.
                //Otherwise, set the URL to null.
                Uri.parse("http://host/path"),
                //TODO: Make sure this auto-generated app URL is correct.
                Uri.parse("android-app://com.technerdshub.vusocial.Activities/http/host/path")
        );
        AppIndex.AppIndexApi.start(client, viewAction);
    }

    @Override
    public void onStop() {
        super.onStop();

        //ATTENTION: This was auto-generated to implement the App Indexing API.
        //See https://g.co/AppIndexing/AndroidStudio for more information.
        Action viewAction = Action.newAction(
                Action.TYPE_VIEW, //TODO: choose an action type.
                "StudentDashboard Page", //TODO: Define a title for the content shown.
                //TODO: If you have web page content that matches this app activity's content,
                //make sure this auto-generated web page URL is correct.
                //Otherwise, set the URL to null.
                Uri.parse("http://host/path"),
                //TODO: Make sure this auto-generated app URL is correct.
                Uri.parse("android-app://com.technerdshub.vusocial.Activities/http/host/path")
        );
        AppIndex.AppIndexApi.end(client, viewAction);
        client.disconnect();
    }

    class ViewPagerAdapter extends FragmentPagerAdapter {
        private final List<TaskFragment> mFragmentList = new ArrayList<>();
        private final List<String> mFragmentTitleList = new ArrayList<>();

        public ViewPagerAdapter(FragmentManager manager) {
            super(manager);
        }

        @Override
        public TaskFragment getItem(int position) {
            return mFragmentList.get(position);
        }

        @Override
        public int getCount() {
            return mFragmentList.size();
        }

        public void addFragment(TaskFragment fragment, String title) {
            mFragmentList.add(fragment);
            mFragmentTitleList.add(title);
        }

        @Override
        public CharSequence getPageTitle(int position) {
            return mFragmentTitleList.get(position);
        }


    }

}

InformationsquelleAutor nabia saroosh | 2016-05-23