Android上的SQLiteOpenHelper.getWriteableDatabase()空指针异常

我在Android中使用SQLite直接,直接的SQL运气很好,但这是我第一次在ContentProvider中包装数据库.我一直在打的时候得到一个空指针异常getWritableDatabase()或getReadableDatabase().这只是我在代码中初始化时犯的一个愚蠢错误,还是存在更大的问题？

public class DatabaseProvider extends ContentProvider {
  ...
  private DatabaseHelper                   databaseHelper;
  private SQLiteDatabase                   db;
  ...
  @Override
  public boolean onCreate() {
    databaseHelper = new DatabaseProvider.DatabaseHelper(getContext());
    return (databaseHelper == null) ? false : true;
  }
  ...
  @Override
  public Uri insert(Uri uri, ContentValues values) {   
    db = databaseHelper.getWritableDatabase(); // NULL POINTER EXCEPTION HERE
    ...
  }
  private static class DatabaseHelper extends SQLiteOpenHelper {
    public static final String DATABASE_NAME = "cogsurv.db";
    public static final int DATABASE_VERSION = 1;

    public static final String[] TABLES = {
      "people", 
      "travel_logs", 
      "travel_fixes",
      "landmarks", 
      "landmark_visits",
      "direction_distance_estimates" 
    };

    // people._id does not AUTOINCREMENT, because it's set based on server's people.id
    public static final String[] CREATE_TABLE_SQL = {
      "CREATE TABLE people (_id INTEGER PRIMARY KEY," + 
                 "server_id INTEGER," +
                 "name VARCHAR(255)," +
                 "email_address VARCHAR(255))",
      "CREATE TABLE travel_logs (_id INTEGER PRIMARY KEY AUTOINCREMENT," +
                                "server_id INTEGER," +
                                "person_local_id INTEGER," +
                                "person_server_id INTEGER," +
                                "start DATE," +
                                "stop DATE," +
                                "type VARCHAR(15)," +
                                "uploaded VARCHAR(1))",
      "CREATE TABLE travel_fixes (_id INTEGER PRIMARY KEY AUTOINCREMENT," +
                                 "datetime DATE, " +
                                 "latitude DOUBLE, " +
                                 "longitude DOUBLE, " +
                                 "altitude DOUBLE," +
                                 "speed DOUBLE," +
                                 "accuracy DOUBLE," +
                                 "travel_mode VARCHAR(50), " +
                                 "person_local_id INTEGER," +
                                 "person_server_id INTEGER," +
                                 "travel_log_local_id INTEGER," +
                                 "travel_log_server_id INTEGER," +
                                 "uploaded VARCHAR(1))",
      "CREATE TABLE landmarks (_id INTEGER PRIMARY KEY AUTOINCREMENT," +
                              "server_id INTEGER," +
                              "name VARCHAR(150)," +
                              "latitude DOUBLE," +
                              "longitude DOUBLE," +
                              "person_local_id INTEGER," +
                              "person_server_id INTEGER," +
                              "uploaded VARCHAR(1))",
      "CREATE TABLE landmark_visits (_id INTEGER PRIMARY KEY AUTOINCREMENT," +
                                    "server_id INTEGER," +
                                    "person_local_id INTEGER," +
                                    "person_server_id INTEGER," +
                                    "landmark_local_id INTEGER," +
                                    "landmark_server_id INTEGER," +
                                    "travel_log_local_id INTEGER," +
                                    "travel_log_server_id INTEGER," +
                                    "datetime DATE," +
                                    "number_of_questions_asked INTEGER," +
                                    "uploaded VARCHAR(1))",
      "CREATE TABLE direction_distance_estimates (_id INTEGER PRIMARY KEY AUTOINCREMENT," +
                                                 "server_id INTEGER," +
                                                 "person_local_id INTEGER," +
                                                 "person_server_id INTEGER," +
                                                 "travel_log_local_id INTEGER," +
                                                 "travel_log_server_id INTEGER," +
                                                 "landmark_visit_local_id INTEGER," +
                                                 "landmark_visit_server_id INTEGER," +
                                                 "start_landmark_local_id INTEGER," +
                                                 "start_landmark_server_id INTEGER," +
                                                 "target_landmark_local_id INTEGER," +
                                                 "target_landmark_server_id INTEGER," +
                                                 "datetime DATE," +
                                                 "direction_estimate DOUBLE," +
                                                 "distance_estimate DOUBLE," +
                                                 "uploaded VARCHAR(1))"
    };

    public DatabaseHelper(Context context) {
      super(context, DATABASE_NAME, null, DATABASE_VERSION);
      Log.v(Constants.TAG, "DatabaseHelper()");
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
      Log.v(Constants.TAG, "DatabaseHelper.onCreate() starting");

      // create the tables
      int length = CREATE_TABLE_SQL.length;
      for (int i = 0; i < length; i++) {
        db.execSQL(CREATE_TABLE_SQL[i]);
      }
      Log.v(Constants.TAG, "DatabaseHelper.onCreate() finished");
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
      for (String tableName : TABLES) {
        db.execSQL("DROP TABLE IF EXISTS" + tableName);
      }
      onCreate(db);
    }
  }
}

一如既往,感谢您的帮助!

-

不确定这个细节是否有帮助,但是这里的LogCat显示了异常:

删除了死的ImageShack链接

而不是:

databaseHelper = new DatabaseProvider.DatabaseHelper(getContext());

尝试:

databaseHelper = new DatabaseProvider.DatabaseHelper(this);

看看是否有帮助.

如果没有,你可以发布NullPointerException堆栈跟踪吗？