ContextWrapper.getResources nullpointer beim Hinzufügen von Zeilen zu TableLayout

Question

Ich habe die Frage bearbeitet, um die Antwort zu reflektieren. Ich habe ein new Artists() jedes Mal instanziiert, wenn die DatabaseHelper-Methode getArtists() aufgerufen wurde. So löschte ich artists = new Artists(); in getArtists() in der DatabaseHelper Klasse. Anstatt es immer wieder instanziieren zu müssen, habe ich gelernt, wie man den Kontext im Konstruktor verwendet. So bekomme ich die Referenz Artists() im DatabaseHelper Konstruktor, so.

public DatabaseController(Context c){ 
     myContext = c; 
     artists = (Artists) myContext; 
    } 

// ORIGINAL FRAGE/CODE

Ich bin ein NPE bei android.content.ContextWrapper.getResources(ContextWrapper.java:89) bekommen und ich kann nicht herausfinden, was los ist. Viele Suchen haben darauf hingewiesen, dass das Problem darin besteht, dass getResources irgendwo aufgerufen wird, das nicht onCreate ist, aber getResources nirgendwo anrufe.

Ich versuche, Daten aus der Datenbank abzurufen und programmgesteuert ein TableLayout daraus zu füllen.

Hier ist die Künstleraktivität.

public class Artists extends AppCompatActivity 
     implements NavigationView.OnNavigationItemSelectedListener { 

    private DatabaseController dbcon; 
    public TableLayout table; 
    public static int artistPopulateCatcher = 0; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_artists); 
     table = (TableLayout)findViewById(R.id.table_artists); 

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

     DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_artists); 


     ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
       this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close); 
     drawer.setDrawerListener(toggle); 
     toggle.syncState(); 

     NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view); 
     navigationView.setNavigationItemSelectedListener(this); 

     if(artistPopulateCatcher == 0) { 
      dbcon = new DatabaseController(this); 
      dbcon.open(); 
      dbcon.getArtists(); 
      dbcon.close(); 
     } 
    } 

    public void AddNewArtistDialog(View view) { 


     final AlertDialog.Builder builder = new AlertDialog.Builder(this); 
     final View layout = LayoutInflater.from(this).inflate(R.layout.addartistdialog, null); 
     builder.setView(layout) 
       .setPositiveButton("Submit", new DialogInterface.OnClickListener() { 

        @Override 
        public void onClick(DialogInterface dialog, int which) { 

         final EditText name = (EditText) layout.findViewById(R.id.edittext_artist_name); 
         final EditText email = (EditText) layout.findViewById(R.id.edittext_artist_email); 
         final CheckBox is21 = (CheckBox) layout.findViewById(R.id.checkBox_is21); 

         String artistIs21; 
         String artistName; 
         String artistEmail; 

         if (is21.isChecked()){ 
          artistIs21 = "Yes"; 
          artistName = name.getText().toString(); 
          artistEmail = email.getText().toString(); 
          dbcon.open(); 
          dbcon.AddArtist(artistName, artistIs21, artistEmail); 
          dbcon.close(); 

         } else{ 
          artistIs21 = "No"; 
          artistName = name.getText().toString(); 
          artistEmail = email.getText().toString(); 
          dbcon.open(); 
          dbcon.AddArtist(artistName, artistIs21, artistEmail); 
          dbcon.close(); 
         } 
         dialog.cancel(); 

        } 
       }) 
       .setNegativeButton("Cancel", new DialogInterface.OnClickListener() { 
        @Override 
        public void onClick(DialogInterface dialog, int which) { 
         dialog.cancel(); 
        } 
       }); 
     builder.show(); 
    } 

    public void PopulateArtist(String artist, int draw, String is21, String email){ 
     Log.d("TAG", artist+", "+draw+", "+is21); 


     TableRow tr = new TableRow(this); 
     tr.setLayoutParams(new TableLayout.LayoutParams(TableLayout.LayoutParams.MATCH_PARENT, TableLayout.LayoutParams.WRAP_CONTENT)); 

     TextView artistName = new TextView(this); 
     TextView artistDraw = new TextView(this); 
     TextView artistIs21 = new TextView(this); 
     TextView artistEmail = new TextView(this); 

     artistName.setText(artist); 
     artistDraw.setText(String.valueOf(draw)); 
     artistIs21.setText(is21); 
     artistEmail.setText(email); 

     tr.addView(artistName); 
     tr.addView(artistDraw); 
     tr.addView(artistIs21); 
     tr.addView(artistEmail); 

     table.addView(tr, new TableLayout.LayoutParams(TableLayout.LayoutParams.MATCH_PARENT, TableLayout.LayoutParams.MATCH_PARENT)); 
    } 

My Database Controller:

public class DatabaseController{ 

    private DatabaseHelper dbHelper; 
    public Context myContext; 
    private SQLiteDatabase db; 
    public Artists artists; 

    public DatabaseController(Context c){ 
     myContext = c; 
    } 

    public DatabaseController open() throws SQLException{ 
     dbHelper = new DatabaseHelper(myContext); 
     db = dbHelper.getWritableDatabase(); 
     return this; 
    } 

    public void close(){ 
     dbHelper.close(); 
    } 

    public void AddArtist(String name, String is21, String email){ 
     ContentValues values = new ContentValues(); 
     values.put(DatabaseHelper.KEY_NAME, name); 
     values.put(DatabaseHelper.KEY_IS21, is21); 
     values.put(DatabaseHelper.KEY_EMAIL, email); 
     values.put(DatabaseHelper.KEY_DRAW, 0); 
     db.insert(DatabaseHelper.TABLE_ARTISTS, null, values); 
    } 

    public Cursor getArtists() { 
     artists.artistPopulateCatcher = 1; 
     artists = new Artists(); 
     Cursor cursor = db.rawQuery("SELECT * FROM Artists", null); 
     cursor.moveToFirst(); 
     while (cursor.isAfterLast() == false){ 
      String name = cursor.getString(cursor.getColumnIndex("Name")); 
      int draw = cursor.getInt(cursor.getColumnIndex("Draw")); 
      String is21 = cursor.getString(cursor.getColumnIndex("Is21")); 
      String email = cursor.getString(cursor.getColumnIndex("Email")); 

      artists.PopulateArtist(name, draw, is21, email); 

      cursor.moveToNext(); 
     } 
     return cursor; 
    } 

    public int updateArtist(int _id, String artistName, int draw, String is21, String email){ 
     ContentValues cv = new ContentValues(); 
     cv.put(dbHelper.KEY_ID, _id); 
     cv.put(dbHelper.KEY_NAME, artistName); 
     cv.put(dbHelper.KEY_DRAW, draw); 
     cv.put(dbHelper.KEY_IS21, is21); 
     cv.put(dbHelper.KEY_EMAIL, email); 
     int i = db.update(dbHelper.TABLE_ARTISTS, cv, dbHelper.KEY_ID + " = "+_id, null); 
     return i; 
    } 
} 

Und hier ist der Stacktrace:

java.lang.RuntimeException: Unable to start activity ComponentInfo{scarycat.promotertools/scarycat.promotertools.Artists}: java.lang.NullPointerException 
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2237) 
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2286) 
                      at android.app.ActivityThread.access$800(ActivityThread.java:144) 
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1246) 
                      at android.os.Handler.dispatchMessage(Handler.java:102) 
                      at android.os.Looper.loop(Looper.java:212) 
                      at android.app.ActivityThread.main(ActivityThread.java:5137) 
                      at java.lang.reflect.Method.invokeNative(Native Method) 
                      at java.lang.reflect.Method.invoke(Method.java:515) 
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:902) 
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:718) 
                      at dalvik.system.NativeStart.main(Native Method) 
                     Caused by: java.lang.NullPointerException 
                      at android.content.ContextWrapper.getResources(ContextWrapper.java:89) 
                      at android.view.ContextThemeWrapper.getResources(ContextThemeWrapper.java:78) 
                      at android.support.v7.app.AppCompatActivity.getResources(AppCompatActivity.java:542) 
                      at android.view.View.<init>(View.java:3569) 
                      at android.view.ViewGroup.<init>(ViewGroup.java:459) 
                      at android.widget.LinearLayout.<init>(LinearLayout.java:168) 
                      at android.widget.TableRow.<init>(TableRow.java:61) 
                      at scarycat.promotertools.Artists.PopulateArtist(Artists.java:112) 
                      at scarycat.promotertools.DatabaseController.getArtists(DatabaseController.java:53) 
                      at scarycat.promotertools.Artists.onCreate(Artists.java:55) 
                      at android.app.Activity.performCreate(Activity.java:5231) 
                      at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087) 
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2201) 
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2286)  
                      at android.app.ActivityThread.access$800(ActivityThread.java:144)  
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1246)  
                      at android.os.Handler.dispatchMessage(Handler.java:102)  
                      at android.os.Looper.loop(Looper.java:212)  
                      at android.app.ActivityThread.main(ActivityThread.java:5137)  
                      at java.lang.reflect.Method.invokeNative(Native Method)  
                      at java.lang.reflect.Method.invoke(Method.java:515)  
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:902)  
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:718)  
                      at dalvik.system.NativeStart.main(Native Method)  

Answer 1

Ich war einen neuen Künstler Instanziieren() in den getArtists() -Methode in DatabaseHelper. Ich habe diese Zeile gelöscht und im Konstruktor habe ich artists = (Artists) myContext;