应用程序在getWritableDatabase崩溃：NullPointerException

我试图做一个涉及数据库的应用程序。我使用的是ContentProvider，当它尝试getWritableDatabase时，它在查询方法中崩溃。它返回一个NullPointerException。我知道Context是非空的，因为这似乎是这类问题的主要原因。应用程序在getWritableDatabase崩溃：NullPointerException

这里是ContentProvider的代码：

package com.corvus.corvusenterprises.digimonapp; 

import android.content.ContentProvider; 
import android.content.ContentResolver; 
import android.content.ContentUris; 
import android.content.ContentValues; 
import android.content.Context; 
import android.content.UriMatcher; 
import android.database.Cursor; 
import android.database.SQLException; 
import android.database.sqlite.SQLiteDatabase; 
import android.database.sqlite.SQLiteQueryBuilder; 
import android.net.Uri; 
import android.text.TextUtils; 
import android.util.Log; 

import java.util.Arrays; 
import java.util.HashSet; 

import static com.corvus.corvusenterprises.digimonapp.DBHelper.presentDigimon; 

/** 
* Created by Jack on 01/05/2017. 
*/ 

public class DigimonContentProvider extends ContentProvider { 
    private static DigimonContentProvider instance; 
    private DBHelper dbHelper; 
    private SQLiteDatabase db; 

    private static final int DIGIMON = 10; 
    private static final int DIGIMON_ID = 20; 
    private static final int ATTACKS = 30; 
    private static final int ATTACKS_ID = 40; 
    private static final int EVOLUTIONS = 50; 
    private static final int EVOLUTIONS_ID = 60; 

    private static final String AUTHORITY = "com.corvus.corvusenterprises.digimonapp"; 

    private static final String BASE_PATH_DIGIMON = "digimon"; 
    private static final String BASE_PATH_ATTACKS = "attacks"; 
    private static final String BASE_PATH_EVOLUTIONS = "evolutions"; 

    public static final Uri CONTENT_URI_DIGIMON = Uri.parse("content://" + AUTHORITY + "/" + BASE_PATH_DIGIMON); 
    public static final Uri CONTENT_URI_ATTACKS = Uri.parse("content://" + AUTHORITY + "/" + BASE_PATH_ATTACKS); 
    public static final Uri CONTENT_URI_EVOLUTIONS = Uri.parse("content://" + AUTHORITY + "/" + BASE_PATH_EVOLUTIONS); 

    public static final String CONTENT_TYPE = ContentResolver.CURSOR_DIR_BASE_TYPE + "/digimon"; 
    public static final String CONTENT_ITEM_TYPE = ContentResolver.CURSOR_ITEM_BASE_TYPE + "/digimon"; 

    private static final UriMatcher sURIMatcher = new UriMatcher(UriMatcher.NO_MATCH); 

    static { 
     sURIMatcher.addURI(AUTHORITY, BASE_PATH_DIGIMON, DIGIMON); 
     sURIMatcher.addURI(AUTHORITY, BASE_PATH_DIGIMON + "/#", DIGIMON_ID); 
     sURIMatcher.addURI(AUTHORITY, BASE_PATH_ATTACKS, ATTACKS); 
     sURIMatcher.addURI(AUTHORITY, BASE_PATH_ATTACKS + "/#", ATTACKS_ID); 
     sURIMatcher.addURI(AUTHORITY, BASE_PATH_EVOLUTIONS, EVOLUTIONS); 
     sURIMatcher.addURI(AUTHORITY, BASE_PATH_EVOLUTIONS + "/#", EVOLUTIONS_ID); 
    } 

    private DigimonContentProvider() 
    { 

    } 
    public static DigimonContentProvider getInstance() { 
     if (instance == null) 
      instance = new DigimonContentProvider(); 
     return instance; 
    } 
    @Override 
    public boolean onCreate() { 
     Context ctx = MyApp.getContext(); 
     dbHelper = DBHelper.getInstance(ctx); 

     dbHelper.insertDigimon("Guilmon", "Guilmon", "Child/Rookie", "Virus", "Dinosaur", "TRUE","R.mipmap.guilmon.jpg"); 
     dbHelper.insertDigimon("Growmon", "Growlmon", "Adult/Champion", "Virus", "Bigger Dinosaur", "FALSE","R.mipmap.growmon.jpg"); 
     dbHelper.insertDigimon("Terriermon", "terriermon", "Child/Rookie", "Vaccine", "Dogbunny", "FALSE","R.mipmap.terriermon.jpg"); 
     dbHelper.insertDigimon("Galgomon", "Gargomon", "Adult/Champion", "Vaccine", "Gunbunny", "FALSE","R.mipmap.galgomon.jpg"); 
     dbHelper.insertDigimon("Kyubimon", "Kyubimon", "Adult/Champion", "Data", "9-Tailed Fox", "FALSE","R.mipmap.kyubimon.jpg"); 
     dbHelper.insertDigimon("Taomon", "Taomon", "Perfect/Ultimate", "Data", "Kitsune Miko", "FALSE","R.mipmap.taomon.jpg"); 
     dbHelper.insertDigimon("Impmon", "Impmon", "Child/Rookie", "Virus", "Kid in a purple onesie", "FALSE","R.mipmap.impmon.jpg"); 
     dbHelper.insertDigimon("Beelzebumon", "Beelzemon", "Ultimate/Mega", "Virus", "Demon Lord of Gluttony", "FALSE","R.mipmap.beelzebumon.jpg"); 

     presentDigimon[460] = true; presentDigimon[454] = true; 
     presentDigimon[1019] = true; presentDigimon[374] = true; 
     presentDigimon[572] = true; presentDigimon[1013] = true; 
     presentDigimon[507] = true; presentDigimon[100] = true; 

     dbHelper.insertEvolution("Guilmon", "Growmon", ""); 
     dbHelper.insertEvolution("Terriermon", "Galgomon",""); 
     dbHelper.insertEvolution("Kyubimon", "Taomon",""); 
     dbHelper.insertEvolution("Impmon", "Beelzebumon", "(Warp Evolution)"); 

     dbHelper.insertAttack("Fireball", "Pyro Sphere", "Guilmon", "Explosive Fireball"); 
     dbHelper.insertAttack("Rock Breaker", "Rock Breaker", "Guilmon", "Claw Swipe"); 
     dbHelper.insertAttack("Exhaust Flame", "Pyro Blaster", "Growmon", "Fire Laser"); 
     dbHelper.insertAttack("Plasma Blade", "Dragon Slash", "Growmon", "Forearm Blades"); 
     dbHelper.insertAttack("Blazing Fire", "Bunny Blast", "Terriermon", "Energy Blast"); 
     dbHelper.insertAttack("Petit Twister", "Terrier Tornado", "Terriermon", "Throws Tornado"); 
     dbHelper.insertAttack("Gatling Arm", "Gargo Laser", "Galgomon", "Fires Guns"); 
     dbHelper.insertAttack("Dum Dum Upper", "Bunny Pummel", "Galgomon", "Fires Guns While Punching"); 
     dbHelper.insertAttack("Koenryu", "Dragon Wheel", "Kyubimon", "Fire Dragon"); 
     dbHelper.insertAttack("Onibidama", "Fox-Tail Inferno", "Kyubimon", "Fireballs from the tails"); 
     dbHelper.insertAttack("Bonhitsusen", "Talisman of Light", "Taomon", "Energy Seal Laser"); 
     dbHelper.insertAttack("Oṃ", "Talisman Spell", "Taomon", "Makes a dome shield"); 
     dbHelper.insertAttack("Night of Fire", "Badaboom", "Impmon", "Mini-Fireballs"); 
     dbHelper.insertAttack("Pillar of Fire", "", "Impmon", "Wall of Flames"); 
     dbHelper.insertAttack("Double Impact", "Double Impact", "Beelzebumon", "Fires two bullets"); 
     dbHelper.insertAttack("Darkness Claw", "", "Beelzebumon", "Kills Leomon"); 
     db = dbHelper.getWritableDatabase(); 
     return false; 
    } 

    @Override 
    public Uri insert(Uri uri, ContentValues values) { 
     Uri _uri = null; 
     switch (sURIMatcher.match(uri)) { 
      case DIGIMON: 
       long _ID1 = db.insert(DigimonTable.DIGIMON_TABLE_NAME, "", values); 
       if (_ID1 > 0) { 
        _uri = ContentUris.withAppendedId(CONTENT_URI_DIGIMON, _ID1); 
        MyApp.getContext().getContentResolver().notifyChange(_uri, null); 
       } 
       break; 
      case ATTACKS: 
       long _ID2 = db.insert(AttacksTable.ATTACKS_TABLE_NAME, "", values); 
       if (_ID2 > 0) { 
        _uri = ContentUris.withAppendedId(CONTENT_URI_ATTACKS, _ID2); 
        MyApp.getContext().getContentResolver().notifyChange(_uri, null); 
       } 
       break; 
      case EVOLUTIONS: 
       long _ID3 = db.insert(EvolutionsTable.EVOLUTIONS_TABLE_NAME, "", values); 
       if (_ID3 > 0) { 
        _uri = ContentUris.withAppendedId(CONTENT_URI_EVOLUTIONS, _ID3); 
        MyApp.getContext().getContentResolver().notifyChange(_uri, null); 
       } 
       break; 
      default: 
       throw new SQLException("Failed to insert row into " + uri); 
     } 
     MyApp.getContext().getContentResolver().notifyChange(uri, null); 
     return _uri; 
    } 

    @Override 
    public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) { 
     SQLiteQueryBuilder queryBuilder = new SQLiteQueryBuilder(); 

     int uriType = sURIMatcher.match(uri); 

     checkColumns(projection, uriType); 

     queryBuilder.setTables(DigimonTable.DIGIMON_TABLE_NAME + ", " + EvolutionsTable.EVOLUTIONS_TABLE_NAME + ", " + AttacksTable.ATTACKS_TABLE_NAME); 

     switch (uriType) { 
      case DIGIMON: 
       break; 
      case DIGIMON_ID: 
       queryBuilder.appendWhere(DigimonTable.DIGIMON_COLUMN_ID+"="+uri.getLastPathSegment()); 
      case ATTACKS: 
       break; 
      case ATTACKS_ID: 
       queryBuilder.appendWhere(AttacksTable.ATTACKS_COLUMN_ID+"="+uri.getLastPathSegment()); 
      case EVOLUTIONS: 
       break; 
      case EVOLUTIONS_ID: 
       queryBuilder.appendWhere(EvolutionsTable.EVOLUTIONS_COLUMN_ID+"="+uri.getLastPathSegment()); 
      default: 
       throw new IllegalArgumentException("Unknown URI: "+ uri); 
     } 
     Cursor cursor = queryBuilder.query(db, projection, selection, selectionArgs, null, null, sortOrder); 
     cursor.setNotificationUri(MyApp.getContext().getContentResolver(), uri); 

     return cursor; 
    } 

    @Override 
    public String getType(Uri uri) { 
     return null; 
    } 

    @Override 
    public int delete(Uri uri, String selection, String[] selectionArgs) { 
     int uriType = sURIMatcher.match(uri); 
     int rowsDeleted = 0; 
     switch (uriType) { 
      case DIGIMON: 
       rowsDeleted = db.delete(DigimonTable.DIGIMON_TABLE_NAME, selection, selectionArgs); 
       break; 
      case DIGIMON_ID: 
       String id1 = uri.getLastPathSegment(); 
       if (TextUtils.isEmpty(selection)) { 
        rowsDeleted = db.delete(
          DigimonTable.DIGIMON_TABLE_NAME, 
          DigimonTable.DIGIMON_COLUMN_ID + "=" + id1, 
          null); 
       } else { 
        rowsDeleted = db.delete(
          DigimonTable.DIGIMON_TABLE_NAME, 
          DigimonTable.DIGIMON_COLUMN_ID + "=" + id1 
            + " and " + selection, 
          selectionArgs); 
       } 
       break; 
      case ATTACKS: 
       rowsDeleted = db.delete(AttacksTable.ATTACKS_TABLE_NAME, selection, selectionArgs); 
       break; 
      case ATTACKS_ID: 
       String id2 = uri.getLastPathSegment(); 
       if (TextUtils.isEmpty(selection)) { 
        rowsDeleted = db.delete(
          AttacksTable.ATTACKS_TABLE_NAME, 
          AttacksTable.ATTACKS_COLUMN_ID + "=" + id2, 
          null); 
       } else { 
        rowsDeleted = db.delete(
          AttacksTable.ATTACKS_TABLE_NAME, 
          AttacksTable.ATTACKS_COLUMN_ID + "=" + id2 
            + " and " + selection, 
          selectionArgs); 
       } 
       break; 
      case EVOLUTIONS: 
       rowsDeleted = db.delete(EvolutionsTable.EVOLUTIONS_TABLE_NAME, selection, selectionArgs); 
       break; 
      case EVOLUTIONS_ID: 
       String id3 = uri.getLastPathSegment(); 
       if (TextUtils.isEmpty(selection)) { 
        rowsDeleted = db.delete(
          EvolutionsTable.EVOLUTIONS_TABLE_NAME, 
          EvolutionsTable.EVOLUTIONS_COLUMN_ID + "=" + id3, 
          null); 
       } else { 
        rowsDeleted = db.delete(
          EvolutionsTable.EVOLUTIONS_TABLE_NAME, 
          EvolutionsTable.EVOLUTIONS_COLUMN_ID + "=" + id3 
            + " and " + selection, 
          selectionArgs); 
       } 
       break; 
      default: 
       throw new IllegalArgumentException("Unknown URI: " + uri); 
     } 
     MyApp.getContext().getContentResolver().notifyChange(uri, null); 
     return rowsDeleted; 
    } 

    @Override 
    public int update(Uri uri, ContentValues values, String selection, 
         String[] selectionArgs) { 

     int uriType = sURIMatcher.match(uri); 
     int rowsUpdated = 0; 
     switch (uriType) { 
      case DIGIMON: 
       rowsUpdated = db.update(DigimonTable.DIGIMON_TABLE_NAME, 
         values, 
         selection, 
         selectionArgs); 
       break; 
      case DIGIMON_ID: 
       String id1 = uri.getLastPathSegment(); 
       if (TextUtils.isEmpty(selection)) { 
        rowsUpdated = db.update(DigimonTable.DIGIMON_TABLE_NAME, 
          values, 
          DigimonTable.DIGIMON_COLUMN_ID + "=" + id1, 
          null); 
       } else { 
        rowsUpdated = db.update(DigimonTable.DIGIMON_TABLE_NAME, 
          values, 
          DigimonTable.DIGIMON_COLUMN_ID + "=" + id1 
            + " and " 
            + selection, 
          selectionArgs); 
       } 
       break; 
      case ATTACKS: 
       rowsUpdated = db.update(AttacksTable.ATTACKS_TABLE_NAME, 
         values, 
         selection, 
         selectionArgs); 
       break; 
      case ATTACKS_ID: 
       String id2 = uri.getLastPathSegment(); 
       if (TextUtils.isEmpty(selection)) { 
        rowsUpdated = db.update(AttacksTable.ATTACKS_TABLE_NAME, 
          values, 
          AttacksTable.ATTACKS_COLUMN_ID + "=" + id2, 
          null); 
       } else { 
        rowsUpdated = db.update(AttacksTable.ATTACKS_TABLE_NAME, 
          values, 
          AttacksTable.ATTACKS_COLUMN_ID + "=" + id2 
            + " and " 
            + selection, 
          selectionArgs); 
       } 
       break; 
      case EVOLUTIONS: 
       rowsUpdated = db.update(EvolutionsTable.EVOLUTIONS_TABLE_NAME, 
         values, 
         selection, 
         selectionArgs); 
       break; 
      case EVOLUTIONS_ID: 
       String id3 = uri.getLastPathSegment(); 
       if (TextUtils.isEmpty(selection)) { 
        rowsUpdated = db.update(EvolutionsTable.EVOLUTIONS_TABLE_NAME, 
          values, 
          EvolutionsTable.EVOLUTIONS_COLUMN_ID + "=" + id3, 
          null); 
       } else { 
        rowsUpdated = db.update(EvolutionsTable.EVOLUTIONS_TABLE_NAME, 
          values, 
          EvolutionsTable.EVOLUTIONS_COLUMN_ID + "=" + id3 
            + " and " 
            + selection, 
          selectionArgs); 
       } 
       break; 
      default: 
       throw new IllegalArgumentException("Unknown URI: " + uri); 
     } 
     MyApp.getContext().getContentResolver().notifyChange(uri, null); 
     return rowsUpdated; 
    } 
    private void checkColumns(String[] projection, int uri) { 
     HashSet<String> availableColumns; 
     String[] availableDigimon = { DigimonTable.DIGIMON_COLUMN_ID, 
       DigimonTable.DIGIMON_COLUMN_NAME, DigimonTable.DIGIMON_COLUMN_DUB_NAME, 
       DigimonTable.DIGIMON_COLUMN_LEVEL, DigimonTable.DIGIMON_COLUMN_ATTRIBUTE, 
       DigimonTable.DIGIMON_COLUMN_DESCRIPTION, DigimonTable.DIGIMON_COLUMN_FAVOURITE, 
       DigimonTable.DIGIMON_COLUMN_PATH}; 
     String[] availableAttacks = {AttacksTable.ATTACKS_COLUMN_ID, AttacksTable.ATTACKS_COLUMN_NAME, 
       AttacksTable.ATTACKS_COLUMN_DUB_NAME, AttacksTable.ATTACKS_COLUMN_DIGIMON, 
       AttacksTable.ATTACKS_COLUMN_DESCRIPTION}; 
     String[] availableEvolutions = {EvolutionsTable.EVOLUTIONS_COLUMN_ID,EvolutionsTable.EVOLUTIONS_COLUMN_FROM, 
       EvolutionsTable.EVOLUTIONS_COLUMN_TO, EvolutionsTable.EVOLUTIONS_COLUMN_CONDITIONS}; 
     if (projection != null) { 
      HashSet<String> requestedColumns = new HashSet<String>(
        Arrays.asList(projection)); 
      switch(uri){ 
       case DIGIMON: 
       case DIGIMON_ID: availableColumns = new HashSet<String>(Arrays.asList(availableDigimon)); 
        break; 
       case ATTACKS: 
       case ATTACKS_ID: availableColumns = new HashSet<String>(Arrays.asList(availableAttacks)); 
        break; 
       case EVOLUTIONS: 
       case EVOLUTIONS_ID: availableColumns = new HashSet<String>(Arrays.asList(availableEvolutions)); 
        break; 
       default: availableColumns = new HashSet<String>(Arrays.asList(availableDigimon)); 
      } 
      // check if all columns which are requested are available 
      if (!availableColumns.containsAll(requestedColumns)) { 
       throw new IllegalArgumentException(
         "Unknown columns in projection"); 
      } 
     } 
    } 

    public Cursor defaultMainMenu() 
    { 
     Cursor cursor = MyApp.getContext().getContentResolver().query(CONTENT_URI_DIGIMON, new String[]{DigimonTable.DIGIMON_COLUMN_NAME, DigimonTable.DIGIMON_COLUMN_FAVOURITE}, null, null, DigimonTable.DIGIMON_COLUMN_NAME + " ASC"); 
     int dummy = cursor.getCount(); 
     return cursor; 

    } 
    public Cursor searchMenuQuery(String search) 
    { 
     Cursor cursor = MyApp.getContext().getContentResolver().query(CONTENT_URI_DIGIMON,new String[] {DigimonTable.DIGIMON_COLUMN_NAME,DigimonTable.DIGIMON_COLUMN_FAVOURITE},DigimonTable.DIGIMON_COLUMN_NAME+" = '?'",new String[]{search},DigimonTable.DIGIMON_COLUMN_NAME+" ASC"); 
     int dummy = cursor.getCount(); 
     return cursor; 
    } 
    public Cursor favouritesMenuQuery() 
    { 
     Cursor cursor = MyApp.getContext().getContentResolver().query(CONTENT_URI_DIGIMON,new String[] {DigimonTable.DIGIMON_COLUMN_NAME},DigimonTable.DIGIMON_COLUMN_FAVOURITE+" = true",null,DigimonTable.DIGIMON_COLUMN_NAME+" ASC"); 
     int dummy = cursor.getCount(); 
     return cursor; 
    } 
    public Cursor digimonProfileQuery(String name) 
    { 
     Cursor cursor = MyApp.getContext().getContentResolver().query(CONTENT_URI_DIGIMON,null,DigimonTable.DIGIMON_COLUMN_NAME+" = '?'",new String[]{name},null); 
     int dummy = cursor.getCount(); 
     return cursor; 
    } 
    public Cursor digimonAttacksQuery(String name) 
    { 
     Cursor cursor = MyApp.getContext().getContentResolver().query(CONTENT_URI_ATTACKS,null,AttacksTable.ATTACKS_COLUMN_DIGIMON+" = '?'",new String[]{name},null); 
     int dummy = cursor.getCount(); 
     return cursor; 
    } 
    public Cursor digimonEvolutionFromQuery(String name) 
    { 
     Cursor cursor = MyApp.getContext().getContentResolver().query(CONTENT_URI_EVOLUTIONS,null,EvolutionsTable.EVOLUTIONS_COLUMN_FROM+" = '?'",new String[]{name},null); 
     int dummy = cursor.getCount(); 
     return cursor; 
    } 
    public Cursor digimonEvolutionToQuery(String name) 
    { 
     Cursor cursor = MyApp.getContext().getContentResolver().query(CONTENT_URI_EVOLUTIONS,null,EvolutionsTable.EVOLUTIONS_COLUMN_TO+" = '?'",new String[]{name},null); 
     int dummy = cursor.getCount(); 
     return cursor; 
    } 
}

而这里的logcat的结果：

Process: com.corvus.corvusenterprises.digimonapp, PID: 12198 
       java.lang.RuntimeException: Unable to get provider com.corvus.corvusenterprises.digimonapp.DigimonContentProvider: java.lang.NullPointerException 
        at android.app.ActivityThread.installProvider(ActivityThread.java:5084) 
        at android.app.ActivityThread.installContentProviders(ActivityThread.java:4673) 
        at android.app.ActivityThread.handleBindApplication(ActivityThread.java:4613) 
        at android.app.ActivityThread.access$1800(ActivityThread.java:141) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1298) 
        at android.os.Handler.dispatchMessage(Handler.java:102) 
        at android.os.Looper.loop(Looper.java:136) 
        at android.app.ActivityThread.main(ActivityThread.java:5333) 
        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:895) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:711) 
        at dalvik.system.NativeStart.main(Native Method) 
       Caused by: java.lang.NullPointerException 
        at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:224) 
        at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:164) 
        at com.corvus.corvusenterprises.digimonapp.DigimonContentProvider.onCreate(DigimonContentProvider.java:62) 
        at android.content.ContentProvider.attachInfo(ContentProvider.java:1616) 
        at android.content.ContentProvider.attachInfo(ContentProvider.java:1587) 
        at android.app.ActivityThread.installProvider(ActivityThread.java:5081) 
        at android.app.ActivityThread.installContentProviders(ActivityThread.java:4673) 
        at android.app.ActivityThread.handleBindApplication(ActivityThread.java:4613) 
        at android.app.ActivityThread.access$1800(ActivityThread.java:141) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1298) 
        at android.os.Handler.dispatchMessage(Handler.java:102) 
        at android.os.Looper.loop(Looper.java:136) 
        at android.app.ActivityThread.main(ActivityThread.java:5333) 
        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:895) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:711) 
        at dalvik.system.NativeStart.main(Native Method)

这里的DBHelper代码，在情况下，它可以帮助：

package com.corvus.corvusenterprises.digimonapp; 

    import android.content.ContentValues; 
    import android.content.Context; 
    import android.database.sqlite.SQLiteDatabase; 
    import android.database.sqlite.SQLiteOpenHelper; 

    import static com.corvus.corvusenterprises.digimonapp.DigimonContentProvider.CONTENT_URI_ATTACKS; 
    import static com.corvus.corvusenterprises.digimonapp.DigimonContentProvider.CONTENT_URI_DIGIMON; 
    import static com.corvus.corvusenterprises.digimonapp.DigimonContentProvider.CONTENT_URI_EVOLUTIONS; 

    /** 
    * Created by Jack on 01/05/2017. 
    */ 

    public class DBHelper extends SQLiteOpenHelper { 
     public static final String[]digimonArray = { 
       "Gigantic array of names"}; 
     private static final String DATABASE_NAME = "DigimonDatabase.db"; 
    private static final int version = 1; 
    private static DBHelper instance; 
    public static boolean[]presentDigimon = new boolean[digimonArray.length]; 
    private DBHelper(Context context) { 
     super(context, DATABASE_NAME, null, version); 
    } 
    public static DBHelper getInstance(Context ctx) { 
     if (instance == null) 
      instance = new DBHelper(ctx); 
     return instance; 
    } 
    @Override 
    public void onCreate(SQLiteDatabase db) { 
     DigimonTable.onCreate(db); 
     AttacksTable.onCreate(db); 
     EvolutionsTable.onCreate(db); 
    } 
    public void onUpgrade(SQLiteDatabase db, int oldver, int newVer) 
    { 
     DigimonTable.onUpgrade(db,oldver,newVer); 
     AttacksTable.onUpgrade(db,oldver,newVer); 
     EvolutionsTable.onUpgrade(db,oldver,newVer); 
    } 
    public void insertDigimon(String name, String dub_name, String level, String attribute, String description, String favourite, String path) 
    { 
     DigimonContentProvider dcp = DigimonContentProvider.getInstance(); 
     ContentValues values = new ContentValues(); 
     values.put(DigimonTable.DIGIMON_COLUMN_NAME,name); 
     values.put(DigimonTable.DIGIMON_COLUMN_DUB_NAME,dub_name); 
     values.put(DigimonTable.DIGIMON_COLUMN_LEVEL,level); 
     values.put(DigimonTable.DIGIMON_COLUMN_ATTRIBUTE,attribute); 
     values.put(DigimonTable.DIGIMON_COLUMN_DESCRIPTION,description); 
     values.put(DigimonTable.DIGIMON_COLUMN_FAVOURITE, favourite); 
     values.put(DigimonTable.DIGIMON_COLUMN_PATH,path); 
     dcp.insert(CONTENT_URI_DIGIMON, values); 
    } 
    public void insertAttack(String name, String dub_name, String digimon, String description) 
    { 
     DigimonContentProvider dcp = DigimonContentProvider.getInstance(); 
     ContentValues values = new ContentValues(); 
     values.put(AttacksTable.ATTACKS_COLUMN_NAME, name); 
     values.put(AttacksTable.ATTACKS_COLUMN_DUB_NAME,dub_name); 
     values.put(AttacksTable.ATTACKS_COLUMN_DIGIMON, digimon); 
     values.put(AttacksTable.ATTACKS_COLUMN_DESCRIPTION, description); 
     dcp.insert(CONTENT_URI_ATTACKS, values); 
    } 
    public void insertEvolution(String from, String to, String conditions) 
    { 
     DigimonContentProvider dcp = DigimonContentProvider.getInstance(); 
     ContentValues values = new ContentValues(); 
     values.put(EvolutionsTable.EVOLUTIONS_COLUMN_TO,to); 
     values.put(EvolutionsTable.EVOLUTIONS_COLUMN_FROM,from); 
     values.put(EvolutionsTable.EVOLUTIONS_COLUMN_CONDITIONS,conditions); 
     dcp.insert(CONTENT_URI_EVOLUTIONS, values); 
    } 
}

任何和所有帮助赞赏。如果您需要更多信息，请告诉我。（EDITED）：新版本正在开发中。代码已更新。（EDITED 2）：修正了递归调用的一个可能的问题。

来源

2017-05-08 IronLucario2012

可能重复的[无法确定什么是抛出NullPointer异常]（http://stackoverflow.com/questions/2291159/cant-determine-what-is-throwing-a-nullpointer-exception） –

“应用程序在getWritableDatabase中崩溃：显然，NullPointerException“ - 'dbHelper'为'null'。 – CommonsWare

我敢打赌你'Context ctx = MyApp.getContext（）;'返回null，因为获取上下文的静态方法很糟糕 –

我知道一个事实，即上下文不为空

你怎么知道的？ MyApp.getContext()对我来说很陌生。

先给背景下的ContentProvider的

private Context mContext; 

private DigimonContentProvider(Context context) 
{ 
    this.mContext = context; 
} 

private DigimonContentProvider() { } 


public static DigimonContentProvider getInstance(Context context) { 
    if (instance == null) 
     instance = new DigimonContentProvider(context); 
    return instance; 
} 

@Override 
public boolean onCreate() { 
    dbHelper = DBHelper.getInstance(this.mContext);

但是，你并不需要ContentProvider的有一个数据库，所以尽量让数据库，而它的工作。

来源

2017-05-10 19:02:00

我知道，因为在早期版本中，如果上下文为空，并且一旦我实现了停止显示为问题的MyApp版本，那么我有一个if/else将放出特定消息。 – IronLucario2012

另外，关于如何在没有ContentProvider的情况下创建数据库，我已经将它撕碎并重建了两次。如果可能的话，我宁愿不做第三次。 – IronLucario2012

这只是一个建议。在尝试使用ContentProvider之前，您是否测试过数据库？ –

它扔了NullPointerException，因为您试图直接访问您的ContentProvider方法，而不是使用ContentResolver。

您可以将您在ContentProvider中编写的代码摘要在另一个类中进行访问。这次使用相同的ContentResolver实例。

编辑：
也许你的问题是，你的dbHelper是不是单身，你是通过dbHelper.getInstance(getContext)在insert()方法创建一个它的另一个实例。
尝试仅在onCreate()方法中获取dbHelper的新实例，而不是其他方法。

你可以用这个例子：MoviesContentProvider.java

来源

2017-05-08 15:52:34 jayeshsolanki93

刚才提出的问题。现在堆栈跟踪看起来是这样的：显示java.lang.NullPointerException 在android.database.sqlite.SQLiteOpenHelper.getWritableDatabase（SQLiteOpenHelper在android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked（SQLiteOpenHelper.java:224）： '所致。java：164） at com.corvus.corvusenterprises.digimonapp.DigimonContentProvider.query（DigimonContentProvider.java:126）' – IronLucario2012

@ IronLucario2012检查我的编辑到答案。 – jayeshsolanki93

也nope。 'DBHelper'类是一个单例。而'insert（）'方法甚至不涉及'dbHelper'，错误现在在'onCreate（）'方法的第62行。 – IronLucario2012

应用程序在getWritableDatabase崩溃：NullPointerException

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