App stürzt ab, wenn versucht wird, benutzerdefinierte ActionBar zu verwenden

Question

Ich versuche eine benutzerdefinierte Aktionsleiste zu einer Aktivität mit Registerkarten hinzuzufügen, jedoch stürzt die App ab. Der Code wird in einer leeren Aktivität wie erwartet kompiliert und funktioniert wie erwartet, funktioniert jedoch nicht mit einer Aktivität mit Registerkarten. Ich erhalte den folgenden Fehler.

"Verursacht durch: java.lang.NullPointerException: Der Versuch, virtuelle Methode 'android.view.Window $ Rückruf android.view.Window.getCallback()' auf ein Null-Objekt Verweis aufrufen"

Bitte meine sehen Code unten.

 import android.widget.TextView; 

    public class nearMe extends AppCompatActivity { 


ActionBar actionBar = getSupportActionBar(); 
/** 
* The {@link android.support.v4.view.PagerAdapter} that will provide 
* fragments for each of the sections. We use a 
* {@link FragmentPagerAdapter} derivative, which will keep every 
* loaded fragment in memory. If this becomes too memory intensive, it 
* may be best to switch to a 
* {@link android.support.v4.app.FragmentStatePagerAdapter}. 
*/ 
private SectionsPagerAdapter mSectionsPagerAdapter; 

/** 
* The {@link ViewPager} that will host the section contents. 
*/ 
private ViewPager mViewPager; 

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


    getSupportActionBar().setDisplayOptions(ActionBar.DISPLAY_SHOW_CUSTOM); 
    getSupportActionBar().setDisplayShowCustomEnabled(true); 
    getSupportActionBar().setCustomView(R.layout.custom_line_info); 
    View view = getSupportActionBar().getCustomView(); 

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); 
    setSupportActionBar(toolbar); 
    // Create the adapter that will return a fragment for each of the three 
    // primary sections of the activity. 
    mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager()); 

    // Set up the ViewPager with the sections adapter. 
    mViewPager = (ViewPager) findViewById(R.id.container); 
    mViewPager.setAdapter(mSectionsPagerAdapter); 


    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab); 
    fab.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View view) { 
      Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG) 
        .setAction("Action", null).show(); 
     } 
    }); 

} 


@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_near_me, menu); 
    return true; 
} 

@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); 
} 

/** 
* A placeholder fragment containing a simple view. 
*/ 
public static class PlaceholderFragment extends Fragment { 
    /** 
    * The fragment argument representing the section number for this 
    * fragment. 
    */ 
    private static final String ARG_SECTION_NUMBER = "section_number"; 

    public PlaceholderFragment() { 
    } 

    /** 
    * Returns a new instance of this fragment for the given section 
    * number. 
    */ 
    public static PlaceholderFragment newInstance(int sectionNumber) { 
     PlaceholderFragment fragment = new PlaceholderFragment(); 
     Bundle args = new Bundle(); 
     args.putInt(ARG_SECTION_NUMBER, sectionNumber); 
     fragment.setArguments(args); 
     return fragment; 
    } 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, 
          Bundle savedInstanceState) { 
     View rootView = inflater.inflate(R.layout.fragment_near_me, container, false); 
     TextView textView = (TextView) rootView.findViewById(R.id.section_label); 
     textView.setText(getString(R.string.section_format, getArguments().getInt(ARG_SECTION_NUMBER))); 
     return rootView; 
    } 
} 

/** 
* A {@link FragmentPagerAdapter} that returns a fragment corresponding to 
* one of the sections/tabs/pages. 
*/ 
public class SectionsPagerAdapter extends FragmentPagerAdapter { 

    public SectionsPagerAdapter(FragmentManager fm) { 
     super(fm); 
    } 

    @Override 
    public Fragment getItem(int position) { 
     // getItem is called to instantiate the fragment for the given page. 
     // Return a PlaceholderFragment (defined as a static inner class below). 
     return PlaceholderFragment.newInstance(position + 1); 
    } 

    @Override 
    public int getCount() { 
     // Show 3 total pages. 
     return 3; 
    } 

    @Override 
    public CharSequence getPageTitle(int position) { 
     switch (position) { 
      case 0: 
       return "SECTION 1"; 
      case 1: 
       return "SECTION 2"; 
      case 2: 
       return "SECTION 3"; 
     } 
     return null; 
    } 
} 
} 

Answer 1

Wie es scheint, von der Linie

Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);

, dass Sie bereits eine benutzerdefinierte Symbolleiste in der XML. Um es zu verwenden, müssen Sie:

1. Verwenden Sie ein Thema für die Aktivität ohne Aktionsleiste.

2. Verschieben

   Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); 
   setSupportActionBar(toolbar); 
   

kurz nach setContentView(R.layout.activity_near_me);

3. ändern ActionBar actionBar = getSupportActionBar(); -ActionBar actionBar;
4. Initialisieren der ActionBar Eigenschaft nach setSupportActionBar(toolbar);