android - 为什么我的数据库使应用程序强制关闭但在我清除数据后工作正常？

Question

如果我清除我的应用数据然后运行它，它工作正常。如果我重新打开或重新运行我的应用程序，它会强制关闭并抛出 java.lang.NullPointerException？错误在这一段代码中

private static class DbHelper extends SQLiteOpenHelper{
    public DbHelper(Context context) {
        super(context, DB_NAME, null, DATABASE_VERSION);
        // TODO Auto-generated constructor stub
    }
    @Override
    public void onCreate(SQLiteDatabase db) {
        // TODO Auto-generated method stub
        db.execSQL("CREATE TABLE " + DB_TBL + " (" +
                KEY_ROWID + " INTEGER PRIMARY KEY AUTOINCREMENT, " + 
                KEY_LEVEL + " INTEGER NOT NULL, " + 
                KEY_HEALTH + " INTEGER NOT NULL, " +
                KEY_NAME + " TEXT NOT NULL, " +
                KEY_CRIT + " INTEGER NOT NULL, " +
                KEY_CRIT_RANGE + " INTEGER NOT NULL, " +
                KEY_CRIT_INC + " INTEGER NOT NULL, " +
                KEY_HIT_RANGE + " INTEGER NOT NULL, " +
                KEY_HIT_INC + " INTEGER NOT NULL, " +
                KEY_CHAR_IMG + " INTEGER NOT NULL, " +
                KEY_TOTAL_XP + " INTEGER NOT NULL, " +
                KEY_XP + " INTEGER NOT NULL, " +
                KEY_XP_NEEDED + " INTEGER NOT NULL, " +
                KEY_COINS + " INTEGER NOT NULL, " + 
                KEY_SMALL_POTS + " INTEGER NOT NULL, " +
                KEY_LARGE_POTS + " INTEGER NOT NULL)"
            );

        values = new ContentValues();
        values.put(KEY_NAME, "User1");
        values.put( KEY_LEVEL, 1);
        values.put(KEY_HEALTH, 10);
        values.put(KEY_CRIT, 5);
        values.put(KEY_CRIT_RANGE, 2);
        values.put(KEY_CRIT_INC, 2);
        values.put(KEY_HIT_RANGE, 2);
        values.put(KEY_HIT_INC, 0);
        values.put(KEY_TOTAL_XP, 0);
        values.put(KEY_XP, 0);
        values.put(KEY_XP_NEEDED, 5);
        values.put(KEY_COINS, 5);
        values.put(KEY_SMALL_POTS, 0);
        values.put(KEY_LARGE_POTS, 0);
        values.put(KEY_CHAR_IMG, 1);
        db.insert(DB_TBL,  null, values);

    }    

java.lang.NullPointerException 指向这个

  public int getLevel() {
    open();
    int level = values.getAsInteger(KEY_LEVEL);
    close();
    return level;
}

这是我的堆栈跟踪

01-04 14:45:45.694: W/dalvikvm(20858): threadid=9: thread exiting with uncaught exception (group=0x4001e578)
01-04 14:45:45.694: E/AndroidRuntime(20858): FATAL EXCEPTION: UpdateThread
01-04 14:45:45.694: E/AndroidRuntime(20858): java.lang.NullPointerException
01-04 14:45:45.694: E/AndroidRuntime(20858):    at com.tanukiproductions.battleforchristmas.SQLiteTable.getLevel(SQLiteTable.java:110)
01-04 14:45:45.694: E/AndroidRuntime(20858):    at com.tanukiproductions.battleforchristmas.Profile.<init>(Profile.java:57)
01-04 14:45:45.694: E/AndroidRuntime(20858):    at com.tanukiproductions.battleforchristmas.MainMenuScene.onMenuItemClicked(MainMenuScene.java:37)

这是open()和close()

public static void open() throws SQLException{
    ourDatabase = ourHelper.getWritableDatabase();
}

public static void close() throws SQLException{
    ourHelper.close();
}

Answer 1

由于在至少运行一次应用程序后创建新的 DbHelper 对象时不会调用 onCreate()，因此 values 为 null。

如果您想从表中提取此数据，请使用 SQLiteDatabase#query() .

public int getLevel() {
    int level = -1;
    open();

    Cursor cursor = ourDatabase.query(DB_TBL, new String[] {KEY_LEVEL}, null, null, null, null, null);
    if(cursor.moveToFirst())
        level = cursor.getInt(0); // get the first column from your Select statement, i.e. KEY_LEVEL

    cursor.close();
    close();
    return level;
}

但是这只会返回找到的第一个“级别”，使用 _id 参数来选择特定的行。