java - android.database.CursorIndexOutOfBoundsException - 我的光标为空

Question

所以我一直在尝试在我的 sqlite 数据库中查询我的 Android 应用程序。然而，我的光标似乎也没有像预期的那样工作，因为我可以获得任何结果。

我知道我的数据库中只有 3 个项目，但我在查询中输入的内容是我存储的 3 个项目的有效属性。但还是没有结果。

下面是我的查询函数和数据库模型的代码。

// To get data from DB by querying the items selected
    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};
        //Cursor cursor = db.query(DBHelper.TABLE_NAME,columns,null,null,null,null,null);
        String selectQuery = "SELECT * FROM "+ DBHelper.TABLE_NAME + " WHERE " + DBHelper.FIRST_ATTRIBUTE + "=? "
                + " AND " + DBHelper.SECOND_ATTRIBUTE + "=? " + " AND " + DBHelper.THIRD_ATTRIBUTE + "=? " + " AND " + DBHelper.FOURTH_ATTRIBUTE + "=? "
                + " AND " + DBHelper.FIFTH_ATTRIBUTE + "=?";
        Cursor cursor=db.rawQuery(selectQuery, new String[] {firstSelectionStr, secondSelectionStr, thirdSelectionStr,
                            fourthSelectionStr, fifthSelectionStr});
        StringBuilder buffer = new StringBuilder();

        cursor.moveToFirst();

        if (cursor != null) {

            int tresult = cursor.getCount();

            // Append every data together
            do {
                //int cursorID = cursor.getInt(cursor.getColumnIndex(DBHelper.UID));
                String chosenItem = cursor.getString(cursor.getColumnIndex(DBHelper.CNAME));
                buffer.append(chosenItem + " ");
            } while (cursor.moveToNext());
        /*while (cursor.moveToNext())
        {
            //int cursorID = cursor.getInt(cursor.getColumnIndex(DBHelper.UID));
            String chosenItem = cursor.getString(cursor.getColumnIndex(DBHelper.CNAME));
            buffer.append(chosenItem + " ");
        }*/
        }

        return buffer.toString();
    }

static class DBHelper extends SQLiteOpenHelper
    {
        private static final String DATABASE_NAME = "CraftsAppDatabase.db";    // 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 "+RESULT_TABLE;
        private Context context;

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

        /*public void deleteTable(SQLiteDatabase db) {
            db = getWritableDatabase();
            db.execSQL("DROP TABLE IF EXISTS CraftTools");
        }*/

        public void onCreate(SQLiteDatabase db) {
            db.execSQL(DROP_TABLE);
            db.execSQL(CREATE_OTHER_TABLE);
            db.execSQL(CREATE_TABLE);
            db.execSQL("INSERT INTO " + TABLE_NAME + "(Craft_Name, First_Attribute, Second_Attribute, Third_Attribute, Fourth_Attribute, Fifth_Attribute ) " +
                    "VALUES ('Landscape Drawing', '1', '4','8', '0', '0')");
            db.execSQL("INSERT INTO " + TABLE_NAME + "(Craft_Name, First_Attribute, Second_Attribute, Third_Attribute, Fourth_Attribute, Fifth_Attribute ) " +
                    "VALUES ('Popsicle Sticks House', '2', '3','0', '0', '0')");
            db.execSQL("INSERT INTO " + TABLE_NAME + "(Craft_Name, First_Attribute, Second_Attribute, Third_Attribute, Fourth_Attribute, Fifth_Attribute ) " +
                    "VALUES ('Sunset Painting', '4', '7','10', '0', '0')");

            /*try {
                db.execSQL(CREATE_TABLE);
            } catch (Exception e) {
                Message.message(context,""+e);
            }*/
        }

        @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");
            //onCreate(db);
            /*try {
                Message.message(context,"OnUpgrade");
                db.execSQL(DROP_TABLE);
                onCreate(db);
            }catch (Exception e) {
                Message.message(context,""+e);*/
            }
        }


    }

我的错误日志位于此行下方。我不确定为什么我的结果是空的或者为什么缓冲区中没有放入任何内容。

11-27 22:43:28.898 4502-4502/com.example.android.androidcraftsappprototype E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.android.androidcraftsappprototype, PID: 4502
    android.database.CursorIndexOutOfBoundsException: Index 0 requested, with a size of 0
        at android.database.AbstractCursor.checkPosition(AbstractCursor.java:468)
        at android.database.AbstractWindowedCursor.checkPosition(AbstractWindowedCursor.java:136)
        at android.database.AbstractWindowedCursor.getString(AbstractWindowedCursor.java:50)
        at com.example.android.androidcraftsappprototype.DBAdapter.getData(DBAdapter.java:86)
        at com.example.android.androidcraftsappprototype.SetupPage$2.onClick(SetupPage.java:118)
        at android.view.View.performClick(View.java:6294)
        at android.view.View$PerformClick.run(View.java:24770)
        at android.os.Handler.handleCallback(Handler.java:790)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6494)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)

Answer 1

我认为你的类(class)根据查询返回 0 项..所以你应该写下面的条件

 cursor.moveToFirst(); <--- instead of this

 if(cursor.moveToFirst()){

 // here all your code

}