ViewPager und TabLayout in Fragment. setAdapter für einen Nullobjektverweis

Question

Ich versuche, ViewPager in Fragment hinzuzufügen. Aber wenn ich meine Anwendung starten erhalte ich diese:

java.lang.NullPointerException: Der Versuch, virtuelle Methode ‚Leere android.support.v4.view.ViewPager.setAdapter aufzurufen (android.support.v4.view.PagerAdapter)‘auf ein null-Objekt Referenz

Mein MainFragment:

public class YourTasksFragment extends Fragment { 

@Bind(R.id.viewpager) 
ViewPager viewPager; 

@Bind(R.id.tabs) 
TabLayout tabLayout; 

@Nullable 
@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
    View v = inflater.inflate(R.layout.fragment_your_tasks, container, false); 
    return v; 
} 

@Override 
public void onViewCreated(View view, Bundle savedInstanceState) { 
    super.onViewCreated(view, savedInstanceState); 
    setupViewPager(viewPager); 
    tabLayout.setupWithViewPager(viewPager); 
} 

private void setupViewPager(ViewPager viewPager) { 
    ViewPagerAdapter adapter = new ViewPagerAdapter(getChildFragmentManager()); 
    adapter.addFragment(new OneFragment(), "ONE"); 
    adapter.addFragment(new TwoFragment(), "TWO"); 
    viewPager.setAdapter(adapter); 
} 

class ViewPagerAdapter extends FragmentPagerAdapter { 
    private final List<Fragment> fragmentList = new ArrayList<>(); 
    private final List<String> fragmentTitleList = new ArrayList<>(); 

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

    @Override 
    public Fragment getItem(int position) { 
     return fragmentList.get(position); 
    } 

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

    public void addFragment(Fragment fragment, String title) { 
     fragmentList.add(fragment); 
     fragmentTitleList.add(title); 
    } 

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

Layout:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:app="http://schemas.android.com/apk/res-auto" 
android:layout_width="match_parent" 
android:layout_height="match_parent"> 

    <android.support.design.widget.TabLayout 
     android:id="@+id/tabs" 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     app:tabMode="fixed" 
     app:tabGravity="fill"/> 

<android.support.v4.view.ViewPager 
    android:id="@+id/viewpager" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    app:layout_behavior="@string/appbar_scrolling_view_behavior" /> 

Answer 1

Sie haben vergessen, Butterknife in onCreateView() einzurichten, daher wird die Variable nie initialisiert.

tun:

@Nullable 
@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
    View v = inflater.inflate(R.layout.fragment_your_tasks, container, false); 
    Butterknife.bind(this,v); 
    return v; 
} 

Hoffe, es hilft!

Answer 2

Sie haben vergessen, Butterknife.bind (this, v) zur Methode onCreateView hinzuzufügen. Dies ist erforderlich, um die Ansichten zu binden.

@Nullable 
@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
    View v = inflater.inflate(R.layout.fragment_your_tasks, container, false); 
    Butterknife.bind(this,v); 
    return v; 
}