应用程序在 getWritableDatabase 崩溃：NullPointerException
App crashes at getWritableDatabase: NullPointerException
我正在尝试制作一个涉及数据库的应用程序。我正在使用 ContentProvider，当它尝试获取 WritableDatabase 时，它在查询方法中崩溃了。
它 returns 一个 NullPointerException。我知道 Context 不为空，因为这似乎是造成此类问题的主要原因。
这是 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;
}
}
这是 Logcat 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.access00(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.access00(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)
这里是 DBHelper 代码，希望对您有所帮助：
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);
}
}
感谢所有帮助。如果您需要更多信息，请告诉我。
（已编辑）：正在开发新版本。代码已更新。
（编辑 2）：修复了递归调用可能存在的问题。
它抛出一个 NullPointerException，因为您试图直接访问您的 ContentProvider 方法，而不是使用 ContentResolver 方法。
您可以抽象化您在 ContentProvider 中编写的代码，以便在另一个 class 中访问它。这次使用 ContentResolver 相同的实例。
编辑：
也许你的问题是你的 dbHelper 不是单例，你正在通过 insert() 方法中的 dbHelper.getInstance(getContext) 创建它的另一个实例。
尝试仅在 onCreate() 方法中而不是在其他方法中获取 dbHelper 的新实例。
你可以使用这个例子：MoviesContentProvider.java
I know for a fact that the Context isn't null
你怎么知道的？ MyApp.getContext() 我觉得很奇怪。
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，因此请尝试让数据库在没有它的情况下工作。
我正在尝试制作一个涉及数据库的应用程序。我正在使用 ContentProvider，当它尝试获取 WritableDatabase 时，它在查询方法中崩溃了。 它 returns 一个 NullPointerException。我知道 Context 不为空，因为这似乎是造成此类问题的主要原因。
这是 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;
}
}
这是 Logcat 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.access00(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.access00(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)
这里是 DBHelper 代码，希望对您有所帮助：
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);
}
}
感谢所有帮助。如果您需要更多信息，请告诉我。 （已编辑）：正在开发新版本。代码已更新。 （编辑 2）：修复了递归调用可能存在的问题。
它抛出一个 NullPointerException，因为您试图直接访问您的 ContentProvider 方法，而不是使用 ContentResolver 方法。
您可以抽象化您在 ContentProvider 中编写的代码，以便在另一个 class 中访问它。这次使用 ContentResolver 相同的实例。
编辑：
也许你的问题是你的 dbHelper 不是单例，你正在通过 insert() 方法中的 dbHelper.getInstance(getContext) 创建它的另一个实例。
尝试仅在 onCreate() 方法中而不是在其他方法中获取 dbHelper 的新实例。
你可以使用这个例子：MoviesContentProvider.java
I know for a fact that the Context isn't null
你怎么知道的？ MyApp.getContext() 我觉得很奇怪。
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，因此请尝试让数据库在没有它的情况下工作。