Android - Registerkartenelemente werden nicht erstellt

Question

Ich befolge ein Tutorial, um zu lernen, wie man ein Tab-Layout erstellt. Ich weiß nicht, was ich im folgenden Code gemacht habe, dass es die Tabs nicht ausgibt. Wenn die App ausgeführt wird, wird der Tab nicht angezeigt. Alles andere funktioniert.

Acitvity

public class dashboard extends AppCompatActivity { 

    TabLayout tabs; 
    ViewPager container; 

    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_dashboard); 

     // 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); 

     tabs = (TabLayout) findViewById(R.id.tabs); 
     tabs.setupWithViewPager(container); 
     tabs.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener(){ 
      @Override 
      public void onTabSelected(TabLayout.Tab tab) { 
       container.setCurrentItem(tab.getPosition()); 
      } 
      @Override 
      public void onTabUnselected(TabLayout.Tab tab) { 
       container.setCurrentItem(tab.getPosition()); 
      } 
      @Override 
      public void onTabReselected(TabLayout.Tab tab) { 
       container.setCurrentItem(tab.getPosition()); 
      } 
     }); 
    } 


    @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_dashboard, 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_dashboard, 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 { 
     private String fragments [] = {"Completed", "In Progress"}; 
     public SectionsPagerAdapter(FragmentManager fm) { 
      super(fm); 
     } 

     @Override 
     public Fragment getItem(int position) { 
      switch(position){ 
       case 0: 
        return new dashboard_completed(); 
       case 1: 
        return new dashboard_in_progress(); 
       default: 
        return null; 
      } 
     } 

     @Override 
     public int getCount() { 
      return fragments.length; 
     } 

     @Override 
     public CharSequence getPageTitle(int position) { 
      return fragments[position]; 
     } 
    } 
} 

dashboard_in_progress

public class dashboard_in_progress extends Fragment { 
    @Nullable 
    @Override 
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) { 
     return inflater.inflate(R.layout.dashboard_in_progress, container, false); 
    } 
} 

dashboard_completed

public class dashboard_completed extends Fragment { 
    @Nullable 
    @Override 
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) { 
     return inflater.inflate(R.layout.dashboard_completed, container, false); 
    } 
} 

XML

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

    </android.support.design.widget.TabLayout> 

    <view 
     android:layout_height="match_parent" 
     class="android.support.v4.view.ViewPager" 
     android:id="@+id/container" 
     android:layout_width="match_parent" 
     android:layout_marginTop="48dp"/> 
</android.support.design.widget.CoordinatorLayout> 

Answer 1

Dies ist Ihr Problem.

ViewPager container; 
... 

private ViewPager mViewPager; 
... 

tabs.setupWithViewPager(container); 

Sie erklären zwei ViewPager s, aber du bist nur eine Initialisierung, und versucht, die TabLayout mit dem Null ein Setup.

Entfernen Sie die ViewPager container; Erklärung, und das Setup-Aufruf ändern:

tabs.setupWithViewPager(mViewPager); 

Auch brauchen Sie nicht die OnTabSelectedListener auf dem TabLayout selbst einstellen. Die setupWithViewPager() Methode wird das für Sie behandeln.

Answer 2

gibt es keine Registerkarte zu zeigen. Verwenden Sie dies:

tabLayout.addTab(tabLayout.newTab().setText("Tab 1")); 
    tabLayout.addTab(tabLayout.newTab().setText("Tab 2"));