無法啓動活動：java.lang.NullPointerException：

我對android非常陌生。我正在使用Material Design製作滑動標籤佈局，遵循特定的教程。正如我的標題所述，現在我收到了這個錯誤。我從MainActivity調用Main3Activity活動。如果有人能指出錯誤，更重要的是幫助我糾正錯誤。無法啓動活動：java.lang.NullPointerException：

PS。這是我在這裏的第一篇文章，所以提前致歉。

MainActivity.java

@Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main_appbar); 
     toolbar = (Toolbar) findViewById(R.id.app_bar); 
     setSupportActionBar(toolbar); 




     //getSupprtActionBar().setDisplayShowHomeEnabled(true); 


     NavigationDrawerFragment drawerFragment = (NavigationDrawerFragment) getSupportFragmentManager().findFragmentById(R.id.fragment_navigation_drawer); 

     drawerFragment.setUp(R.id.fragment_navigation_drawer, (DrawerLayout) findViewById(R.id.drawer_layout), toolbar); 


    } 



    @Override 
    public boolean onCreateOptionsMenu(Menu menu) 
    { 
     MenuInflater inflater = getMenuInflater(); 
     inflater.inflate(R.menu.menu, menu); 
     SearchManager searchManager = 
       (SearchManager) getSystemService(Context.SEARCH_SERVICE); 
     SearchView searchView = 
       (SearchView) menu.findItem(R.id.action_search).getActionView(); 
     searchView.setSearchableInfo(
       searchManager.getSearchableInfo(getComponentName())); 

     return true; 

    } 

    @Override 
    public boolean onOptionsItemSelected(MenuItem item) { 

     int id=item.getItemId(); 
     switch(id) 
     { 
      case R.id.menu_all_reminder: 
       if(item.isChecked()) 
        item.setChecked(false); 
       else 
        item.setChecked(true); 
       getActionBar().setBackgroundDrawable(new ColorDrawable(Color.parseColor("#F44336"))); 
       return true; 

      case R.id.menu_ToDo: 
       if(item.isChecked()) 
        item.setChecked(false); 
       else 
        item.setChecked(true); 
       getActionBar().setBackgroundDrawable(new ColorDrawable(Color.parseColor("#03A9F4"))); 
       return true; 

      case R.id.menu_bills: 
       if(item.isChecked()) 
        item.setChecked(false); 
       else 
        item.setChecked(true); 
       getActionBar().setBackgroundDrawable(new ColorDrawable(Color.parseColor("#4CAF50"))); 
       return true; 

      default: 
       return super.onOptionsItemSelected(item); 

     } 
    } 


}

這是Main3Activity，這基本上是與滑動佈局的活性。這是一個點擊即可從抽屜式導航的回收站觀的主要活動

Main3Activity.java

@Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main3); 

     Toolbar toolbar= (Toolbar) findViewById(R.id.app_bar); 
     setSupportActionBar(toolbar); 
     getSupportActionBar().setHomeButtonEnabled(true); 
     getSupportActionBar().setDisplayHomeAsUpEnabled(true); 

     NavigationDrawerFragment drawerFragment=(NavigationDrawerFragment)getSupportFragmentManager().findFragmentById(R.id.fragment_navigation_drawer); 

     drawerFragment.setUp(R.id.fragment_navigation_drawer, (DrawerLayout) findViewById(R.id.drawer_layout), toolbar); 


     mPager = (ViewPager) findViewById(R.id.pager); 

     mPager.setAdapter(new MyPagerAdapter(getSupportFragmentManager())); 
     mTabs = (SlidingTabLayout) findViewById(R.id.tabs); 
    mTabs.setViewPager(mPager); 
    } 


    class MyPagerAdapter extends FragmentPagerAdapter { 
     String[] tabs; 
     public MyPagerAdapter(FragmentManager fm) { 
      super(fm); 
     } 

     @Override 
     public Fragment getItem(int position) { 
      MyFragment myFragment=MyFragment.getInstance(position); 
      return myFragment; 
     } 

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

     @Override 
     public int getCount() { 
      return 6; 
     } 
    } 

    public static class MyFragment extends Fragment { 
     private TextView textView; 
     public static MyFragment getInstance(int position) { 

      MyFragment myFragment = new MyFragment(); 
      Bundle args=new Bundle(); 
      args.putInt("position",position); 
      myFragment.setArguments(args); 
      return myFragment; 

     } 

     @Override 
     public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
      View layout=inflater.inflate(R.layout.fragment_my,container,false); 
      textView=(TextView)layout.findViewById(R.id.position); 
      Bundle bundle=getArguments(); 
      if (bundle!=null) 
      { 
       textView.setText("The Page Selected is" +bundle.getInt("position")); 
      } 
      return layout; 
     } 
    } 

}

這是明顯的現在

<?xml version="1.0" encoding="utf-8"?> 
<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
    package="demo.demo2"> 

    <application 
     android:allowBackup="true" 
     android:icon="@mipmap/ic_launcher" 
     android:label="Remind Me" 
     android:supportsRtl="true" 
     android:theme="@style/AppTheme"> 
     <activity android:name=".MainActivity"> 
      <intent-filter> 
       <action android:name="android.intent.action.MAIN" /> 

       <category android:name="android.intent.category.LAUNCHER" /> 
      </intent-filter> 

      <meta-data 
       android:name="android.app.searchable" 
       android:resource="@xml/searchable" /> 
     </activity> 
     <activity android:name=".SearchResultsActivity"> 
      <intent-filter> 
       <action android:name="android.intent.action.SEARCH" /> 
      </intent-filter> 
     </activity> 
     <activity android:name=".Main2Activity"> 
      <meta-data 
       android:name="android.support.PARENT_ACTIVITY" 
       android:value="Demo.Demo2.MainActivity" /> 
     </activity> 
     <activity android:name=".Main3Activity"> 

     </activity> 
    </application> 

</manifest>

，這是activity_main3.xml

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    xmlns:tools="http://schemas.android.com/tools" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 

    tools:context="demo.demo2.Main3Activity" 
    xmlns:app="http://schemas.android.com/apk/res-auto" 
    android:orientation="vertical"> 

     <android.support.v4.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android" 
     android:id="@+id/drawer_layout" 
     android:layout_width="match_parent" 
     android:layout_height="match_parent"> 

     <LinearLayout 

      android:layout_width="match_parent" 
      android:layout_height="match_parent" 
      android:layout_below="@id/app_bar" 
      android:orientation="vertical" 
      tools:context="demo.demo2.Main3Activity"> 
      <include 
       android:id="@+id/app_bar" 
       layout="@layout/app_bar" /> 

      <tabs.SlidingTabLayout 
       android:id="@+id/tabs" 
       android:layout_width="match_parent" 
       android:layout_height="wrap_content" /> 

      <android.support.v4.view.ViewPager 
       android:id="@+id/pager" 
       android:layout_width="match_parent" 
       android:layout_height="0dp" 
       android:layout_weight="1"/> 





     </LinearLayout> 
     <fragment 
      android:id="@+id/fragment_navigation_drawer" 
      android:layout_width="@dimen/nav_drawer_width" 
      android:layout_height="match_parent" 
      app:layout="@layout/fragment_navigation_drawer" 
      android:layout_gravity="start" 
      android:name="demo.demo2.NavigationDrawerFragment" 
      tools:layout="@layout/fragment_navigation_drawer" /> 
    </android.support.v4.widget.DrawerLayout> 







</LinearLayout>

而logcat中的錯誤

5366-5366/demo.demo2 E/AndroidRuntime: FATAL EXCEPTION: main 
                  Process: demo.demo2, PID: 5366 
                  java.lang.RuntimeException: Unable to start activity ComponentInfo{demo.demo2/demo.demo2.Main3Activity}: java.lang.NullPointerException: Attempt to read from null array 
                   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325) 
                   at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387) 
                   at android.app.ActivityThread.access$800(ActivityThread.java:151) 
                   at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303) 
                   at android.os.Handler.dispatchMessage(Handler.java:102) 
                   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$MethodAndArgsCaller.run(ZygoteInit.java:903) 
                   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698) 
                  Caused by: java.lang.NullPointerException: Attempt to read from null array 
                   at demo.demo2.Main3Activity$MyPagerAdapter.getPageTitle(Main3Activity.java:63) 
                   at tabs.SlidingTabLayout.populateTabStrip(SlidingTabLayout.java:198) 
                   at tabs.SlidingTabLayout.setViewPager(SlidingTabLayout.java:142) 
                   at demo.demo2.Main3Activity.onCreate(Main3Activity.java:45) 
                   at android.app.Activity.performCreate(Activity.java:5990) 
                   at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106) 
                   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2278) 
                   at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)  
                   at android.app.ActivityThread.access$800(ActivityThread.java:151)  
                   at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)  
                   at android.os.Handler.dispatchMessage(Handler.java:102)  
                   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)  
01-19 02:03:52.050 5366-5366/demo.demo2 I/Process: Sending signal. PID: 5366 SIG: 9

謝謝您提前。

來源

2016-01-18 Aprajeeta Sinha

的可能的複製[什麼是空指針異常，怎麼解決呢？（http://stackoverflow.com/questions/218384/what - 它是一個空指針 - 異常和怎麼辦 - 我 - 修復它） –

@ jipr311其實我試着找出錯誤並糾正它。我檢查了鏈接，但找不到解決方案。 –

的問題是：at demo.demo2.Main3Activity$MyPagerAdapter.getPageTitle(Main3Activity.java:63)

你永遠初始化或填充tabs數組，但你嘗試在getPageTitle(int position)方法來使用它：

String[] tabs;

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

我使用s初始化了我的strings.xml文件ame名稱「選項卡」。它會不會在這裏引用。

命名與資源同名的字段不會自動加載所述資源。

如果沒有，那麼我應該在這裏初始化代碼的，的String []選項卡= { 「TAB1」，「TAB2」，「TAB3」}

你可以，但你可以也從資源加載你的字符串數組。您通過Resources類加載資源。在這種情況下，你可能會使用的方法getStringArray (int id)：

class MyPagerAdapter extends FragmentPagerAdapter { 
    String[] tabs; 
    public MyPagerAdapter(FragmentManager fm) { 
     super(fm); 

     tabs = getResources().getStringArray(R.array.tabs); 
    } 
    // ... 
}

來源

2016-01-18 21:10:53

我已經在我的strings.xml中用相同的名稱「tabs」初始化了一個。它會不會在這裏引用。如果不是，那麼我是否應該在代碼中初始化爲： String [] tabs = {「Tab1」，「Tab2」，「Tab3」}; –

@AprajeetaSinha：查看我的更新回答 –

它工作。非常感謝。自2周以來，我一直因此而陷入困境。 –

無法啓動活動：java.lang.NullPointerException：

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