Leere android.support.v4.app.Fragment.setMenuVisibility (boolean)‘auf einer Null-Objekt Referenz

Question

Der Fehler nur zu erscheinen begann, nachdem ich hier mit Fragmenten im Projekt begann

ist mein Code ..

public class MainActivity extends AppCompatActivity { 

private Toolbar toolbar; 
private ViewPager mPager; 
private SlidingTabLayout mTabs; 
private MyPagerAdapter adapter; 

public static final int product_result = 0; 

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

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

    setSupportActionBar(toolbar); 
    assert getSupportActionBar() != null; 
    getSupportActionBar().setDisplayShowHomeEnabled(true); 

    NavigationDrawerFragment navigationDrawerFragment = (NavigationDrawerFragment) 
      getSupportFragmentManager().findFragmentById(R.id.fragment_nav_drawer); 
    navigationDrawerFragment.setUp(R.id.fragment_nav_drawer, (DrawerLayout) findViewById(R.id.drawer_layout), toolbar); 

    mPager = (ViewPager) findViewById(R.id.pager); 
    adapter = new MyPagerAdapter(getSupportFragmentManager()); 
    mPager.setAdapter(adapter); 

    mTabs = (SlidingTabLayout) findViewById(R.id.tabs); 
    mTabs.setDistributeEvenly(true); 
    mTabs.setCustomTabView(R.layout.custom_tab_view, R.id.tabText); 
    int bgColor = ContextCompat.getColor(this, R.color.colorPrimary); 
    mTabs.setBackgroundColor(bgColor); 
    mTabs.setSelectedIndicatorColors(ContextCompat.getColor(MainActivity.this, R.color.colorAccent)); 
    mTabs.invalidate(); 
    mTabs.setViewPager(mPager); 
} 


@Override 
public boolean onCreateOptionsMenu(Menu menu) { 
    getMenuInflater().inflate(R.menu.menu_main, menu); 
    return true; 
} 

@Override 
public boolean onOptionsItemSelected(MenuItem item) { 
    int id = item.getItemId(); 
    if (id == R.id.action_settings) { 

     return true; 
    } 
    if (id == R.id.navigate) { 
     startActivity(new Intent(this, SubActivity.class)); 
    } 
    if (id == R.id.TabActivity) { 
     startActivity(new Intent(this, ActivityUsingTabLibrary.class)); 
    } 
    if (id == R.id.VectorTest) { 
     startActivity(new Intent(this, VectorTestActivity.class)); 
    } 
    return super.onOptionsItemSelected(item); 
} 


class MyPagerAdapter extends FragmentStatePagerAdapter { 
    int icons[] = {R.drawable.home, R.drawable.hot_article, R.drawable.dizzy_person}; 

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

    @Override 
    public Fragment getItem(int position) { 

     Fragment fragment = null; 
     switch(position){ 
      case product_result: 
       fragment = FragmentProduct.newInstance("",""); 
       break; 
     } 
     return fragment; 
    } 

    @Override 
    public CharSequence getPageTitle(int position) { 
     Drawable drawable = ResourcesCompat.getDrawable(getResources(), icons[position], null); 
     drawable.setBounds(0, 0, 36, 36); 
     ImageSpan imageSpan = new ImageSpan(drawable); 
     SpannableString spannableString = new SpannableString(" "); 
     spannableString.setSpan(imageSpan, 0, spannableString.length(), Spanned.SPAN_EXCLUSIVE_EXCLUSIVE); 
     return spannableString; 
    } 

    @Override 
    public int getCount() { 
     return 3; 
    } 
} 

}

das ist mein fragment.class wo im vorbei JSONObject Toast.

public class FragmentProduct extends Fragment { 

public static final String product_url = "http://oasisgroups.com/oApp/product.php"; 

private static final String ARG_PARAM1 = "param1"; 
private static final String ARG_PARAM2 = "param2"; 

private String mParam1; 
private String mParam2; 
private VolleySingleton volleySingleton; 
private ImageLoader imageLoader; 
private RequestQueue requestQueue; 

public FragmentProduct() { 
    // Required empty public constructor 
} 

public static FragmentProduct newInstance(String param1, String param2) { 
    FragmentProduct fragment = new FragmentProduct(); 
    Bundle args = new Bundle(); 
    args.putString(ARG_PARAM1, param1); 
    args.putString(ARG_PARAM2, param2); 
    fragment.setArguments(args); 
    return fragment; 
} 

public static String getRequestUrl(int limit) { 
    return product_url + "&limit=" + limit; 
} 

@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    if (getArguments() != null) { 
     mParam1 = getArguments().getString(ARG_PARAM1); 
     mParam2 = getArguments().getString(ARG_PARAM2); 
    } 

    volleySingleton = VolleySingleton.getInstance(); 
    requestQueue = volleySingleton.getmRequestQueue(); 
    JsonObjectRequest request = new JsonObjectRequest(Request.Method.GET, getRequestUrl(10), 
      new Response.Listener<JSONObject>() { 
       @Override 
       public void onResponse(JSONObject response) { 
        L.t(getActivity(), response.toString()); 
       } 
      }, new Response.ErrorListener() { 
     @Override 
     public void onErrorResponse(VolleyError error) { 

     } 
    }); 
    requestQueue.add(request); 

} 

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

}

stacktrace

02-29 12:10:01.047 17100-17100/com.mydesign.rockstar.materialdesignexample E/AndroidRuntime: FATAL EXCEPTION: main 
Process: com.mydesign.rockstar.materialdesignexample, PID: 17100 
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.app.Fragment.setMenuVisibility(boolean)' on a null object reference 
    at android.support.v4.app.FragmentStatePagerAdapter.instantiateItem(FragmentStatePagerAdapter.java:116) 
    at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:870) 
    at android.support.v4.view.ViewPager.populate(ViewPager.java:1086) 
    at android.support.v4.view.ViewPager.populate(ViewPager.java:952) 
    at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1474) 
    at android.view.View.measure(View.java:18804) 
    at android.widget.LinearLayout.measureVertical(LinearLayout.java:901) 
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:630) 
    at android.view.View.measure(View.java:18804) 
    at android.support.v4.widget.DrawerLayout.onMeasure(DrawerLayout.java:940) 
    at android.view.View.measure(View.java:18804) 
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5954) 
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:194) 
    at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:135) 
    at android.view.View.measure(View.java:18804) 
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5954) 
    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465) 
    at android.widget.LinearLayout.measureVertical(LinearLayout.java:748) 
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:630) 
    at android.view.View.measure(View.java:18804) 
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5954) 
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:194) 
    at android.view.View.measure(View.java:18804) 
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5954) 
    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465) 
    at android.widget.LinearLayout.measureVertical(LinearLayout.java:748) 
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:630) 
    at android.view.View.measure(View.java:18804) 
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5954) 
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:194) 
    at com.android.internal.policy.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2643) 
    at android.view.View.measure(View.java:18804) 
    at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2112) 
    at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1228) 
    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1464) 
    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1119) 
    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6060) 
    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:858) 
    at android.view.Choreographer.doCallbacks(Choreographer.java:670) 
    at android.view.Choreographer.doFrame(Choreographer.java:606) 
    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:844) 
    at android.os.Handler.handleCallback(Handler.java:746) 
    at android.os.Handler.dispatchMessage(Handler.java:95) 
    at android.os.Looper.loop(Looper.java:148) 
    at android.app.ActivityThread.main(ActivityThread.java:5443) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618) 

i auch das gleiche Problem in dieser link gesehen und ich seine Lösung gelten, aber es wird nicht für mich arbeiten .. Ich bin mir immer noch stecken, helfen. also überprüfen Sie meinen Code und schlagen Sie mir vor, was ich vermisse.

Answer 1

oh ja .. ich habe endlich meinen Fehler gefunden .. vor allem gibt es keinen Fehler in meinem Code. alles ist richtig.

Ich habe drei Registerkarte Layout und ich m übergeben nur für eine tablayout und andere zwei werden null, so muss ich drei Schalter Fallanweisung anwenden.

public Fragment getItem(int position) { 

    Fragment fragment = null; 
    switch(position){ 
     case product_result: 
      fragment = FragmentProduct.newInstance("",""); 
      break; 
    } 
    return fragment; 
} 

statt

public Fragment getItem(int num) { 
     Fragment fragment = null; 
     switch (num) { 
      case TAB_PRODUCT_RESULT: 
       fragment = FragmentProduct.newInstance("", ""); 
       break; 
      case TAB_SECOND: 
       fragment = MyFragment.getInstance(num); 
       break; 
      case TAB_THIRD: 
       fragment = MyFragment.getInstance(num); 
       break; 
     } 
     return fragment; 
    } 

thats it ..

Answer 2

Ich denke, das Problem ist in der public Fragment getItem(int position) Methode Ihrer MyPagerAdapter. Ihr Code-Snippet gibt null Fragmente zurück.

Fragment fragment = null; 
switch(position){ 
    case product_result: 
     fragment = FragmentProduct.newInstance("",""); 
     break; 
    } 
return fragment; 

Sie nur ein echtes Fragment für die Position 0, erhalten, weil product_result-0 initialisiert wird. In allen anderen Fällen gibt es null zurück. Ändern Sie das obige Code-Snippet, um immer eine Fragment-Instanz zurückzugeben, die nicht null ist.