Android Studio getWritableDatabase(); 导致我的应用程序崩溃

Question

所以我一直在尝试使用getData()方法进行查询，每当我运行调试时，我都可以看到它与dbHelper.getWritableDatabase()行一起崩溃。

我以为我是在onCreate()方法中创建数据库，所以我不确定发生了什么。

我的代码在下面。 我将不胜感激任何帮助！

public String getData(int firstSelection, int secondSelection, int thirdSelection,
                          int fourthSelection, int fifthSelection)
    {
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        String firstSelectionStr, secondSelectionStr, thirdSelectionStr, fourthSelectionStr, fifthSelectionStr;

        firstSelectionStr = Integer.toString(firstSelection);
        secondSelectionStr = Integer.toString(secondSelection);
        thirdSelectionStr = Integer.toString(thirdSelection);
        fourthSelectionStr = Integer.toString(fourthSelection);
        fifthSelectionStr = Integer.toString(fifthSelection);


        String[] columns = {DBHelper.UID,DBHelper.CNAME};

        String selectQuery = "SELECT " + DBHelper.CNAME + " FROM "+ "CraftsAppDatabase" + " WHERE First_Attribute=? "
                + " AND Second_Attribute=? " + " AND Third_Attribute=? " + " AND Fourth_Attribute=? "
                + " AND Fifth_Attribute=? ";
        Cursor cursor=db.rawQuery(selectQuery, new String[] {firstSelectionStr, secondSelectionStr, thirdSelectionStr,
                            fourthSelectionStr, fifthSelectionStr});
        StringBuilder buffer = new StringBuilder();

        // Append every data together
        while (cursor.moveToNext())
        {

            String chosenItem = cursor.getString(cursor.getColumnIndex(DBHelper.CNAME));
            buffer.append(chosenItem + "/n");
        }
        return buffer.toString();
    }

static class DBHelper extends SQLiteOpenHelper
    {
        private static final String DATABASE_NAME = "CraftsAppDatabase";    // Database Name
        private static final String TABLE_NAME = "CraftTools";   // Table Name
        private static final String RESULT_TABLE = "Result";   // Table Name
        private static final int DATABASE_Version = 1;    // Database Version
        private static final String UID="_id";     // Column I (Primary Key)
        private static final String CNAME = "Craft_Name";    //Column II
        private static final String RESULT = "Result_Name";    //Column II
        private static final String FIRST_ATTRIBUTE = "First_Attribute";    //Column III
        private static final String SECOND_ATTRIBUTE = "Second_Attribute";    //Column IV
        private static final String THIRD_ATTRIBUTE = "Third_Attribute";    //Column V
        private static final String FOURTH_ATTRIBUTE = "Fourth_Attribute";    //Column VI
        private static final String FIFTH_ATTRIBUTE = "Fifth_Attribute";    //Column VII
        private static final String CREATE_TABLE = "CREATE TABLE "+TABLE_NAME+
                " ("+UID+" INTEGER PRIMARY KEY AUTOINCREMENT, "+CNAME+" VARCHAR(255)" +
                ", "+FIRST_ATTRIBUTE+" VARCHAR(255), "+SECOND_ATTRIBUTE+" VARCHAR(255)" +
                ", "+THIRD_ATTRIBUTE+" VARCHAR(255), "+FOURTH_ATTRIBUTE+" VARCHAR(255)" +
                ", "+FIFTH_ATTRIBUTE+" VARCHAR(255));";
        private static final String CREATE_OTHER_TABLE = "CREATE TABLE "+RESULT_TABLE+
                " ("+UID+" INTEGER PRIMARY KEY AUTOINCREMENT, "+RESULT+" VARCHAR(255));";
        private static final String DROP_TABLE ="DROP TABLE IF EXISTS "+TABLE_NAME;
        private Context context;

        public DBHelper(Context context) {
            super(context, DATABASE_NAME, null, DATABASE_Version);
            this.context=context;
        }


        public void onCreate(SQLiteDatabase db) {
            db.execSQL(CREATE_TABLE);
            db.execSQL(CREATE_OTHER_TABLE);
            db.execSQL("INSERT INTO " + TABLE_NAME + "(CNAME, First_Attribute, Second_Attribute, Third_Attribute, Fourth_Attribute, Fifth_Attribute ) " +
                    "VALUES ('Landscape Drawing', '1', '4','8', 'NONE', 'NONE')");
            db.execSQL("INSERT INTO " + TABLE_NAME + "(CNAME, First_Attribute, Second_Attribute, Third_Attribute, Fourth_Attribute, Fifth_Attribute ) " +
                    "VALUES ('Popsicle Sticks House', '2', '3','NONE', 'NONE', 'NONE')");
            db.execSQL("INSERT INTO " + TABLE_NAME + "(CNAME, First_Attribute, Second_Attribute, Third_Attribute, Fourth_Attribute, Fifth_Attribute ) " +
                    "VALUES ('Sunset Painting', '4', '7','10', 'NONE', 'NONE')");

        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            db.execSQL(DROP_TABLE);
            onCreate(db);
            if (newVersion > oldVersion) {
                db.execSQL("ALTER TABLE CraftTools ADD COLUMN FIRST_ATTRIBUTE INTEGER DEFAULT 0");
                db.execSQL("ALTER TABLE CraftTools ADD COLUMN SECOND_ATTRIBUTE INTEGER DEFAULT 0");
                db.execSQL("ALTER TABLE CraftTools ADD COLUMN THIRD_ATTRIBUTE INTEGER DEFAULT 0");
                db.execSQL("ALTER TABLE CraftTools ADD COLUMN FOURTH_ATTRIBUTE INTEGER DEFAULT 0");
                db.execSQL("ALTER TABLE CraftTools ADD COLUMN FIFTH_ATTRIBUTE INTEGER DEFAULT 0");
            }
        }

Answer 1

DATABASE_NAME没有.db扩展名。 那可能是个问题。 由于未初始化dbHelper，可能会出现另一个问题。

Answer 2

这是获取句柄和查询的方法：

public DBHelper extends SQLiteOpenHelper {

    private static final String DATABASE_NAME     = "crafts.db"; 
    private static final String TABLE_CRAFT_TOOLS = "craft_tools";
    private static final String KEY_CRAFT_NAME    = "craft_name";

    protected static SQLiteDatabase db = null;

    /** Constructor */
    public SqliteBaseHelper(Context context, String name, CursorFactory factory, int version) {
        super(context, DATABASE_NAME, factory, DATABASE_VERSION);
        if(db == null) {db = getWritableDatabase();}
    }

    /** this method possibly belongs into the helper class */
    public String getString(int firstSelection, int secondSelection, int thirdSelection, int fourthSelection, int fifthSelection) {

        StringBuilder sb = new StringBuilder();

        String sql = "SELECT " + KEY_CRAFT_NAME + " FROM " + TABLE_CRAFT_TOOLS + " WHERE " +
            "First_Attribute=? AND " +
            "Second_Attribute=? AND " +
            "Third_Attribute=? AND " +
            "Fourth_Attribute=? AND " +
            "Fifth_Attribute=? ";

        String[] selectionArgs = new String[] {
            Integer.toString(firstSelection),
            Integer.toString(secondSelection),
            Integer.toString(thirdSelection),
            Integer.toString(fourthSelection),
            Integer.toString(fifthSelection)
        };

        try {
            Cursor cursor = db.rawQuery(sql, selectionArgs);
            if (cursor.moveToFirst()) {
                do {
                    sb.append(cursor.getString(cursor.getColumnIndex(KEY_CRAFT_NAME)) + "/n");
                } while(cursor.moveToNext());
            } else {
                Log.w(LOG_TAG, "no crafts found.");
            }
        } catch (SQLiteException e) {
            Log.e(LOG_TAG, e.getMessage());
        } finally {
            if (! cursor.isClosed()) {
                cursor.close();
            }
        }
        return sb.toString();
    }

    ...
}

Answer 3

我终于想通了。 以下命令中的CNAME应该是Craft_Name 。

db.execSQL("INSERT INTO " + TABLE_NAME + "(CNAME, First_Attribute, Second_Attribute, Third_Attribute, Fourth_Attribute, Fifth_Attribute ) " +
                    "VALUES ('Landscape Drawing', '1', '4','8', 'NONE', 'NONE')");