NullPointerException ViewPager SetAdapter

Question

我正在添加一個選項卡視圖或（ViewPager）到我正在處理的應用程序中的Fragment。

我想把標籤查看聯繫人片段

我打開抽屜式導航，和你看到的選項列表裏面...

首頁

Services

聯繫

一切你點擊進入片段

然後該分段加載.xml文件，相應地類.xml文件裏面的一切程序。

我下面的在線教程[點擊這裏] [3]

顯然，這2年多前了。自那時起，Android代碼發生了變化。我從現在開始有了更多的錯誤。

我遇到的問題與getSupportFragmentManager（），並getActionBar（）在這一點真的很困惑，所有的進口都在那裏。它不會承認這兩個。顯然，這讓我覺得缺少一些東西，但是我不確定需要讓編譯器看到那些需要的方法。

當ViewPager setAdapter被設置時，我仍然得到Null。

我想要完成的是一個選項卡視圖，其中有兩個選項卡用於聯繫人和社交媒體。如果我可以簡單瞭解標籤頁正常工作所需的內容。

我已經搜索了一些問題，他們沒有完全涉及到我的具體問題，所以我在尋求幫助。任何幫助肯定是讚賞的。

FragmentContact

package com.megliosolutions.bitsnbytes.Fragments; 

import android.app.Activity; 
import android.os.Bundle; 
import android.support.v4.app.FragmentActivity; 
import android.support.v4.app.FragmentManager; 
import android.support.v4.view.ViewPager; 
import android.support.v7.app.ActionBar; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 

import com.megliosolutions.bitsnbytes.MainActivity; 
import com.megliosolutions.bitsnbytes.R; 
import com.megliosolutions.bitsnbytes.ViewPagerClasses.TabsPagerAdapter; 

/** 
* Created by Jarvis on 6/21/15. 
*/ 
public class FragmentContact extends Fragment { 

    private ViewPager viewPager; 
    TabsPagerAdapter mAdapter; 
    private ActionBar actionBar; 

    private String[] tabs = {"Contact", "Social Media"}; 

    public static FragmentContact newInstance(){ 

     FragmentContact fragment = new FragmentContact(); 
     return fragment; 

    } 

    public FragmentContact(){}; 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, 
          Bundle savedInstanceState) { 

     View rootView = inflater.inflate(R.layout.fragment_contact, container, false); 

     LoadTabs(rootView); 

     return rootView; 
    } 

    private void LoadTabs(View rootView) { 
     FragmentManager fragmentManager = getSupportFragmentManager(); 
     // Initilization 
     viewPager = (ViewPager) rootView.findViewById(R.id.pager); 
     actionBar = getActionBar(); 
     mAdapter = new TabsPagerAdapter(fragmentManager); 

     viewPager.setAdapter(mAdapter); 
     actionBar.setHomeButtonEnabled(false); 
     actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS); 

     // Adding Tabs 
     for (String tab_name : tabs) { 
      actionBar.addTab(actionBar.newTab().setText(tab_name) 
        .setTabListener((ActionBar.TabListener) this)); 
     } 
    } 

    @Override 
    public void onAttach(FragmentActivity activity) { 
     super.onAttach(activity); 

     ((MainActivity) activity).onSectionAttached(5); 
    } 


} 

TabsPagerAdapter

package com.megliosolutions.bitsnbytes.ViewPagerClasses; 


import android.support.v4.app.Fragment; 
import android.support.v4.app.FragmentManager; 
import android.support.v4.app.FragmentPagerAdapter; 
import android.view.View; 

/** 
* Created by Jarvis on 6/28/15. 
*/ 
public class TabsPagerAdapter extends FragmentPagerAdapter { 

    public TabsPagerAdapter(FragmentManager fm) { 

     super(fm); 
    } 

    @Override 
    public Fragment getItem(int index) { 

     switch (index) { 
      case 0: 
       // Contact fragment activity 
       return new ContactFragment(); 
      case 1: 
       // Social Media fragment activity 
       return new SocialMediaFragment(); 

     } 

     return null; 
    } 

    @Override 
    public int getCount() { 
     // get item count - equal to number of tabs 
     return 2; 
    } 

    @Override 
    public boolean isViewFromObject(View view, Object object) { 
     return false; 
    } 

} 

MAINACTIVITY

package com.megliosolutions.bitsnbytes; 

import android.app.Activity; 
import android.os.Bundle; 
import android.support.v4.app.ActionBarDrawerToggle; 
import android.support.v4.app.Fragment; 
import android.support.v4.app.FragmentManager; 
import android.support.v4.widget.DrawerLayout; 
import android.support.v7.app.ActionBar; 
import android.support.v7.app.ActionBarActivity; 
import android.view.LayoutInflater; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.View; 
import android.view.ViewGroup; 

import com.megliosolutions.bitsnbytes.Fragments.FragmentAbout; 
import com.megliosolutions.bitsnbytes.Fragments.FragmentContact; 
import com.megliosolutions.bitsnbytes.Fragments.FragmentHome; 
import com.megliosolutions.bitsnbytes.Fragments.FragmentProducts; 
import com.megliosolutions.bitsnbytes.Fragments.FragmentServices; 
import com.megliosolutions.bitsnbytes.Fragments.FragmentWarranties; 


public class MainActivity extends ActionBarActivity 
     implements NavigationDrawerFragment.NavigationDrawerCallbacks { 


    /** 
    * Fragment managing the behaviors, interactions and presentation of the navigation drawer. 
    */ 
    private NavigationDrawerFragment mNavigationDrawerFragment; 






    /** 
    * Used to store the last screen title. For use in {@link #restoreActionBar()}. 
    */ 
    private CharSequence mTitle; 
    private ActionBarDrawerToggle mDrawerToggle; 

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

     mNavigationDrawerFragment = (NavigationDrawerFragment) 
       getSupportFragmentManager().findFragmentById(R.id.navigation_drawer); 
     mTitle = getTitle(); 

     // Set up the drawer. 
     mNavigationDrawerFragment.setUp(
       R.id.navigation_drawer, 
       (DrawerLayout) findViewById(R.id.drawer_layout)); 


    } 

    @Override 
    public void onNavigationDrawerItemSelected(int position) { 
     // update the main content by replacing fragments 
     FragmentManager fragmentManager = getSupportFragmentManager(); 

     if(position == 0) { 
      fragmentManager.beginTransaction() 
        .replace(R.id.container, FragmentHome.newInstance()) 
        .commit(); 
     } 
     else if(position == 1){ 
      fragmentManager.beginTransaction() 
        .replace(R.id.container, FragmentServices.newInstance()) 
        .commit(); 
     } 
     else if(position == 2){ 
      fragmentManager.beginTransaction() 
        .replace(R.id.container, FragmentProducts.newInstance()) 
        .commit(); 
     } 

     else if(position == 3){ 
      fragmentManager.beginTransaction() 
        .replace(R.id.container, FragmentWarranties.newInstance()) 
        .commit(); 
     } 

     else if(position == 4){ 
      fragmentManager.beginTransaction() 
        .replace(R.id.container, FragmentContact.newInstance()) 
        .commit(); 
     } 
     else if(position == 5){ 
      fragmentManager.beginTransaction() 
        .replace(R.id.container, FragmentAbout.newInstance()) 
        .commit(); 
     } 




    } 



    public void onSectionAttached(int number) { 
     switch (number) { 
      case 1: 
       mTitle = getString(R.string.title_section1); 
       break; 
      case 2: 
       mTitle = getString(R.string.title_section2); 
       break; 
      case 3: 
       mTitle = getString(R.string.title_section3); 
       break; 
      case 4: 
       mTitle = getString(R.string.title_section4); 
       break; 
      case 5: 
       mTitle = getString(R.string.title_section5); 
       break; 
      case 6: 
       mTitle = getString(R.string.title_section6); 
     } 
    } 

    public void restoreActionBar() { 
     ActionBar actionBar = getSupportActionBar(); 
     actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_STANDARD); 
     actionBar.setDisplayShowTitleEnabled(true); 
     actionBar.setTitle(mTitle); 
    } 


    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     if (!mNavigationDrawerFragment.isDrawerOpen()) { 
      // Only show items in the action bar relevant to this screen 
      // if the drawer is not showing. Otherwise, let the drawer 
      // decide what to show in the action bar. 
      getMenuInflater().inflate(R.menu.main, menu); 
      restoreActionBar(); 
      return true; 
     } 
     return super.onCreateOptionsMenu(menu); 
    } 

    @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"; 

     /** 
     * 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; 
     } 

     public PlaceholderFragment() { 
     } 

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

     @Override 
     public void onAttach(Activity activity) { 
      super.onAttach(activity); 
      ((MainActivity) activity).onSectionAttached(
        getArguments().getInt(ARG_SECTION_NUMBER)); 
     } 
    } 

} 

現在再次是在onNavigationDrawerItemSelected的FragmentContact.newInstance（）（）

06-28 15:35:24.695 11744-11744/com.megliosolutions.bitsnbytes E/AndroidRuntime﹕ FATAL EXCEPTION: main 
    Process: com.megliosolutions.bitsnbytes, PID: 11744 
    java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.view.ViewPager.setAdapter(android.support.v4.view.PagerAdapter)' on a null object reference 
      at com.megliosolutions.bitsnbytes.Fragments.FragmentContact.LoadTabs(FragmentContact.java:55) 
      at com.megliosolutions.bitsnbytes.Fragments.FragmentContact.onCreateView(FragmentContact.java:43) 
      at android.support.v4.app.Fragment.performCreateView(Fragment.java:1789) 
      at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:955) 
      at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1138) 
      at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:740) 
      at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1501) 
      at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:458) 
      at android.os.Handler.handleCallback(Handler.java:739) 
      at android.os.Handler.dispatchMessage(Handler.java:95) 
      at android.os.Looper.loop(Looper.java:135) 
      at android.app.ActivityThread.main(ActivityThread.java:5254) 
      at java.lang.reflect.Method.invoke(Native Method) 
      at java.lang.reflect.Method.invoke(Method.java:372) 
      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903) 
      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698) 

Answer 1

從logcat的錯誤的問題了明確ViewPager在R.layout.fragment_contact不存在。請確認。