Java getWritableDatabase:NullPointerException上的应用程序崩溃

我正在尝试制作一个包含数据库的应用程序。我使用的是ContentProvider，当它试图获取WritableDatabase时，它在查询方法中崩溃。 它返回一个NullPointerException。我知道上下文不是空的，因为这似乎是造成此类问题的主要原因

以下是ContentProvider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;
    }
}

以下是DBHelper代码，以防有帮助：

    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);
    }
}

感谢您的帮助。如果你需要更多的信息，请告诉我。 （已编辑）：正在编写新版本。代码已更新。

---

（已编辑2）：修复了递归调用可能出现的问题。

它会抛出一个

NullPointerException

，因为您正试图直接访问

ContentProvider

方法，而不是使用

ContentResolver

进行相同操作

您可以抽象在

ContentProvider

中编写的代码，以便在另一个类中访问它。这一次使用

ContentResolver

实例实现相同的功能

编辑：
可能您的问题是您的

dbHelper

不是单例，您正在通过

insert（）

方法中的

dbHelper.getInstance（getContext）

创建它的另一个实例。
仅在

onCreate（）

方法中尝试获取

dbHelper

的新实例，而不要在其他方法中

您可以使用以下示例：

我知道上下文不是空的

你怎么知道的

MyApp.getContext（）

对我来说很奇怪

尝试将上下文提供给ContentProvider

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，您不需要ContentProvider来拥有数据库，因此请尝试在没有它的情况下让数据库正常工作

“应用程序在getWritableDatabase:NullPointerException时崩溃”——显然，

dbHelper

是

null

。我打赌

Context ctx=MyApp.getContext（）

返回null，因为用于获取上下文的静态方法是错误的，这只是解决了问题。现在stacktrace看起来是这样的：

，原因是：android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked（SQLiteOpenHelper.java:224）的java.lang.NullPointerException位于android.database.sqlite.SQLiteOpenHelper.getWritableDatabase（SQLiteOpenHelper.java:164）位于com.corvus.corvusenterprises.digimonaper.DigimonContentProvider.query（DigimonContentProvider.java:126）

也不是。

DBHelper

类是一个单例类。

insert（）

方法甚至不涉及

DBHelper

，错误现在出现在

onCreate（）中的第62行

method。我在主要问题中添加了DBHelper代码，以防万一。我知道这一点，因为在早期版本中，如果上下文为空，我有一个if/else，它会发出一条特定消息，一旦我实现了MyApp版本，它就不再显示为问题。另外，关于在没有ContentProvider的情况下创建数据库，我已经阅读了y把它撕成碎片，然后从地上重建了两次。如果可能的话，我不想再做第三次。这只是一个建议。在尝试将ContentProvider捆绑在数据库上之前，您测试过数据库吗？而且，“DBHelper”应该是“帮助”的使用

SQLiteDatabase

对象。为什么在ContentProvider中会有一个单独浮动的对象？因此，尽管我在四个小时前尝试了这个精确的解决方案，但它失败了，最终还是出现了一些放入getContext（）的排列某个地方似乎已经修复了它。不知何故。仍然有错误，但它们完全无关。谢谢！

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);