getApplicationContext() возвращает null, но работает в других действиях

Question

Я использую базу данных SQLite, и всякий раз, когда я ее называю, мне нужно передать контекст. Обычно я делаю это с помощью getApplicationContext(), который работает в других действиях. В моем текущем классе он просто возвращает null. Помогите!

04-06 16:46:19.523: E/AndroidRuntime(4279): Process: com.example.schoolandrevisiontimetable, PID: 4279 
04-06 16:46:19.523: E/AndroidRuntime(4279): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.schoolandrevisiontimetable/com.example.schoolandrevisiontimetable.Input_slessontime}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.content.Context.getApplicationContext()' on a null object reference 
04-06 16:46:19.523: E/AndroidRuntime(4279):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2225) 
04-06 16:46:19.523: E/AndroidRuntime(4279):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2388) 
04-06 16:46:19.523: E/AndroidRuntime(4279):  at android.app.ActivityThread.access$800(ActivityThread.java:148) 
04-06 16:46:19.523: E/AndroidRuntime(4279):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1292) 
04-06 16:46:19.523: E/AndroidRuntime(4279):  at android.os.Handler.dispatchMessage(Handler.java:102) 
04-06 16:46:19.523: E/AndroidRuntime(4279):  at android.os.Looper.loop(Looper.java:135) 
04-06 16:46:19.523: E/AndroidRuntime(4279):  at android.app.ActivityThread.main(ActivityThread.java:5312) 
04-06 16:46:19.523: E/AndroidRuntime(4279):  at java.lang.reflect.Method.invoke(Native Method) 
04-06 16:46:19.523: E/AndroidRuntime(4279):  at java.lang.reflect.Method.invoke(Method.java:372) 
04-06 16:46:19.523: E/AndroidRuntime(4279):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:901) 
04-06 16:46:19.523: E/AndroidRuntime(4279):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696) 
04-06 16:46:19.523: E/AndroidRuntime(4279): Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.content.Context.getApplicationContext()' on a null object reference 
04-06 16:46:19.523: E/AndroidRuntime(4279):  at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:105) 
04-06 16:46:19.523: E/AndroidRuntime(4279):  at com.example.schoolandrevisiontimetable.Input_slessontime.getAmountOfDaysUsed(Input_slessontime.java:95) 
04-06 16:46:19.523: E/AndroidRuntime(4279):  at com.example.schoolandrevisiontimetable.Input_slessontime.<init>(Input_slessontime.java:30) 
04-06 16:46:19.523: E/AndroidRuntime(4279):  at java.lang.reflect.Constructor.newInstance(Native Method) 
04-06 16:46:19.523: E/AndroidRuntime(4279):  at java.lang.Class.newInstance(Class.java:1572) 
04-06 16:46:19.523: E/AndroidRuntime(4279):  at android.app.Instrumentation.newActivity(Instrumentation.java:1088) 
04-06 16:46:19.523: E/AndroidRuntime(4279):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2215) 
04-06 16:46:19.523: E/AndroidRuntime(4279):  ... 10 more 

Вот класс она возвращается нуль в пакете com.example.schoolandrevisiontimetable;

import java.util.List; 

import com.astuetz.PagerSlidingTabStrip; 


import Database.DatabaseHelper; 
import Database.MC_sschoolday; 
import android.app.Activity; 
import android.app.ActionBar; 
import android.app.Fragment; 
import android.content.Context; 
import android.os.Bundle; 
import android.support.v4.app.FragmentActivity; 
import android.support.v4.app.FragmentManager; 
import android.support.v4.app.FragmentPagerAdapter; 
import android.support.v4.view.ViewPager; 
import android.util.TypedValue; 
import android.view.LayoutInflater; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.View; 
import android.view.ViewGroup; 
import android.os.Build; 

public class Input_slessontime extends FragmentActivity { 
    DatabaseHelper db; 
    String[] days = new String[getAmountOfDaysUsed()]; 
    private PagerSlidingTabStrip tabs; 
    private ViewPager pager; 
    private MyPagerAdapter adapter; 


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


     tabs = (PagerSlidingTabStrip) findViewById(R.id.tabs); 
     pager = (ViewPager) findViewById(R.id.pager); 
     adapter = new MyPagerAdapter(getSupportFragmentManager()); 

     final int pageMargin = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 4, getResources() 
       .getDisplayMetrics()); 
     pager.setPageMargin(pageMargin); 

     tabs.setViewPager(pager); 


     if (savedInstanceState == null) { 
      getFragmentManager().beginTransaction() 
        .add(R.id.container, new PlaceholderFragment()).commit(); 
     } 
    } 

    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     // Inflate the menu; this adds items to the action bar if it is present. 
     getMenuInflater().inflate(R.menu.input_slessontime, 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(); 
     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 { 

     public PlaceholderFragment() { 
     } 

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

    public int getAmountOfDaysUsed(){ 
     db = new DatabaseHelper(getApplicationContext()); 

     List<MC_sschoolday> MC_sschoolday = db.getAllSSchoolDays(); //gets all the lessons and stores them in a list 

     int amountOfDaysUsed=0; 

     MC_sschoolday[] sday = new MC_sschoolday[7]; 
     for (int i =0; i<7; i++){ 
      sday[i]=MC_sschoolday.get(i); //stores the lessons in an array 

     } 

     for (int i =0; i<7; i++){ 
      if(sday[i].getUsed().equals("y")){ 
       amountOfDaysUsed++; 
      } 
     } 

     db.close(); 
     return amountOfDaysUsed; 
    } 
    public void getTitles(){ 
     db = new DatabaseHelper(getApplicationContext()); 
     MC_sschoolday[] sday = new MC_sschoolday[7]; 
     List<MC_sschoolday> schoolday = db.getAllSSchoolDays(); 

     int usedCount2=0; 
     for (int i =0; i< db.getAllSSchoolDays().size(); i++){ 
      sday[i]=schoolday.get(i); 
      if(sday[i].getUsed().equals("y")){ 
       days[usedCount2] = sday[i].getschool_day(); 
       usedCount2++; 
      } 
     } 
     db.close(); 
    } 


    public class MyPagerAdapter extends FragmentPagerAdapter { 



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

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

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

     public android.support.v4.app.Fragment switchFragmentDay(int num) { 
      DatabaseHelper db; 
      db = new DatabaseHelper(getApplicationContext()); 
      MC_sschoolday[] sday = new MC_sschoolday[7]; 
      List<MC_sschoolday> schoolday = db.getAllSSchoolDays(); 
      int usedCount1=getAmountOfDaysUsed(); 


      int [] dayID = new int[usedCount1]; 

      int usedCount2=0; 
      for (int i =0; i< db.getAllSSchoolDays().size(); i++){ 
       sday[i]=schoolday.get(i); 
       if(sday[i].getUsed().equals("y")){ 
        dayID[usedCount2] = (int) sday[i].getSchool_day_id(); 
        usedCount2++; 
       } 
      } 
      db.close(); 
      switch (dayID[num]){ 
      case 1: 
       return new Input_slessontime_monday(); 
      case 2: 
       return new Input_slessontime_tuesday(); 
      case 3: 
       return new Input_slessontime_wednesday(); 
      case 4: 
       return new Input_slessontime_thursday(); 
      case 5: 
       return new Input_slessontime_friday(); 
      case 6: 
       return new Input_slessontime_saturday(); 
      case 7: 
       return new Input_slessontime_sunday(); 
      } 
      return null; 

     } 

     @Override 
     public android.support.v4.app.Fragment getItem(int position) { 

      switch (position){    
      case 0: 
       return switchFragmentDay(0); 
      case 1: 
       return switchFragmentDay(1); 
      case 2: 
       return switchFragmentDay(2); 
      case 3: 
       return switchFragmentDay(3); 
      case 4: 
       return switchFragmentDay(4); 
      case 5: 
       return switchFragmentDay(5); 
      case 6: 
       return switchFragmentDay(6); 

      } 

     return null; 
     } 

    } 


} 

благодарит за вашу помощь!

Answer 1

String[] days = new String[getAmountOfDaysUsed()]; 

Вы используете активность как Context слишком рано, член инициализации переменной. Вам нужно подождать до onCreate() или позже в жизненном цикле деятельности.